UNIVERSITY OF CALOOCAN CITY
Biglang Awa St., Corner Catleya St., EDSA, Caloocan City
COLLEGE OF EDUCATION
Anatomy and Physiology
SUBJECT CODE:
TOPIC OR LESSON:
WEEK:
SUB-TOPIC/S:
MBS 313
Introduction to Anatomy and Physiology
2
1. Nature of Anatomy and Physiology
2. Descriptive Terms
3. Planes and Axes
4. Symmetry
5. Metamerism & Segmentation
6. Cephalization
7. Homology & Analogy
OVERVIEW OF THE TOPIC
Anatomy and physiology are two of the most basic terms and areas of
study in the life sciences. Anatomy refers to the internal and external structures of
the body and their physical relationships, whereas physiology refers to the study
of the functions of those structures. Human anatomy studies the way that every
part of a human, from molecules to bones, interacts to form a functional whole.
Human physiology is the study of the mechanical, physical, and biochemical
processes that support the body’s function. Together, anatomy and physiology
explain the structure and function of the different components of the human
body to describe what it is and how it works.
An understanding of anatomy and physiology is not only fundamental to
any career in the health professions, but it can also benefit your own health.
Familiarity with the human body can help you make healthful choices and
prompt you to take appropriate action when signs of illness arise. Your knowledge
in this field will help you understand news about nutrition, medications, medical
devices, and procedures and help you understand genetic or infectious diseases.
a.
b.
compare and contrast anatomy and physiology;
familiarize oneself with different terms used in Anatomy and Physiology; and
c.
name the different planes, axes, symmetry, segmentation, cephalization,
homology, and analogy of the human body.
At the end of the lesson, students should be able to:
a. define & differentiate anatomy from physiology;
b. identify the descriptive terms used in anatomy and physiology; and
c. discuss planes, axes, symmetry, segmentation, cephalization,
homology & analogy.
INTRODUCTION TO ANATOMY AND PHYSIOLOGY
Our fascinating journey through the human body begins with an overview of the
meanings of anatomy and physiology, followed by a discussion of the organization of
the human body and the properties that it shares with all living things. Next, you will
discover how the body regulates its own internal environment; this unceasing process,
called homeostasis, is a major theme in every chapter of this book. Finally, we introduce
the basic vocabulary that will help you speak about the body in a way that is
understood by scientists and health-care professionals alike.
Anatomy is the scientific study of the body’s structures. Some of these structures
are very small and can only be observed and analyzed with the assistance of a
microscope. Other larger structures can readily be seen, manipulated, measured, and
weighed. The word “anatomy” comes from a Greek root that means “to cut apart”.
Human anatomy was first studied by observing the exterior of the body and observing
the wounds of soldiers and other injuries. Later, physicians could dissect bodies of the
dead to augment their knowledge. When a body is dissected, its structures are cut
apart to observe their physical attributes and their relationships to one another. Like
most scientific disciplines, anatomy has areas of specialization. Gross anatomy is the
study of the larger structures of the body, those visible without the aid of magnification.
Macro- means “large,” thus, gross anatomy is also referred to as macroscopic anatomy.
In contrast, micro- means “small,” and microscopic anatomy is the study of structures
that can be observed only with the use of a microscope or other magnification
devices. Microscopic anatomy includes cytology, the study of cells and histology, the
study of tissues.
Physiology is the scientific study of the chemistry and physics of the structures of
the body and the ways in which they work together to support the functions of life.
Much of the study of physiology centers on the body’s tendency toward homeostasis.
Homeostasis is the state of steady internal conditions maintained by living things. The
study of physiology certainly includes observation, both with the naked eye and with
microscopes, as well as manipulations and measurements.
DESCRIPTIVE TERMS USED IN ANATOMY AND PHYSIOLOGY
Directional Terms
Certain directional anatomical terms appear throughout this and any other
anatomy textbook. These terms are essential for describing the relative locations of
different body structures. For instance, an anatomist might describe one band of tissue
as “inferior to” another or a physician might describe a tumor as “superficial to” a
deeper body structure. Commit these terms to memory to avoid confusion when you
are studying or describing the locations of body parts.
1. Anterior (or ventral) Describes the front or direction toward the front of the
body. The toes are anterior to the foot.
2. Posterior (or dorsal) Describes the back or direction toward the back of
the body. The popliteus is posterior to the patella.
3. Superior (or cranial) describes a position above or higher than another
part of the body proper. The orbits are superior to the oris.
4. Inferior (or caudal) describes a position below or lower than another part
of the body proper; near or toward the tail (in humans, the coccyx, or
lowest part of the spinal column). The pelvis is inferior to the abdomen.
5. Lateral describes the side or direction toward the side of the body. The
thumb (pollex) is lateral to the digits.
6. Medial describes the middle or direction toward the middle of the body.
The hallux is the medial toe.
7. Proximal describes a position in a limb that is nearer to the point of
attachment or the trunk of the body. The brachium is proximal to the
antebrachium.
8. Distal describes a position in a limb that is farther from the point of
attachment or the trunk of the body. The crus is distal to the femur.
9. Superficial describes a position closer to the surface of the body. The skin is
superficial to the bones.
10. Deep describes a position farther from the surface of the body. The brain
is deep to the skull.
Planes
A section is a two-dimensional surface of a three-dimensional structure that has
been cut. Modern medical imaging devices enable clinicians to obtain “virtual
sections” of living bodies. Body sections can be correctly interpreted, however, only if
the viewer understands the plane along which the section was made. A plane is an
imaginary two-dimensional surface that passes through the body. There are three
planes commonly referred to in anatomy and medicine.
1. The sagittal plane is the plane that divides the body or an organ vertically
into right and left sides. If this vertical plane runs directly down the middle
of the body, it is called the midsagittal or median plane. If it divides the
body into unequal right and left sides, it is called a parasagittal plane or
less commonly a longitudinal section.
2. The frontal plane is the plane that divides the body or an organ into an
anterior (front) portion and a posterior (rear) portion. The frontal plane is
often referred to as a coronal plane. (“Corona” is Latin for “crown.”)
3. The transverse plane is the plane that divides the body or organ
horizontally into upper and lower portions. Transverse planes produce
images referred to as cross sections.
Body Cavities
The body maintains its internal organization by means of membranes, sheaths,
and other structures that separate compartments. The dorsal (posterior) cavity and the
ventral (anterior) cavity are the largest body compartments. These cavities contain
and protect delicate internal organs, and the ventral cavity allows for significant
changes in the size and shape of the organs as they perform their functions. The lungs,
heart, stomach, and intestines, for example, can expand and contract without
distorting other tissues or disrupting the activity of nearby organs.
Subdivisions of the Posterior (Dorsal) and Anterior (Ventral) Cavities
The posterior (dorsal) cavity, the cranial cavity houses the brain, and the spinal
cavity (or vertebral cavity) encloses the spinal cord. Just as the brain and spinal cord
make up a continuous, uninterrupted structure, the cranial and spinal cavities that
house them are also continuous. The brain and spinal cord are protected by the bones
of the skull and vertebral column and by cerebrospinal fluid, a colorless fluid produced
by the brain, which cushions the brain and spinal cord within the posterior (dorsal)
cavity.
The anterior (ventral) cavity has two main subdivisions: the thoracic cavity and
the abdominopelvic cavity. The thoracic cavity is the more superior subdivision of the
anterior cavity, and it is enclosed by the rib cage. The thoracic cavity contains the
lungs and the heart, which is located in the mediastinum. The diaphragm forms the floor
of the thoracic cavity and separates it from the more inferior abdominopelvic cavity.
The abdominopelvic cavity is the largest cavity in the body. Although no membrane
physically divides the abdominopelvic cavity, it can be useful to distinguish between
the abdominal cavity, the division that houses the digestive organs, and the pelvic
cavity, the division that houses the organs of reproduction.
Symmetry
Symmetry is the balanced arrangement of body parts or shapes around a
central point or axis. That is, the size, shape, and relative location on one side of a
dividing line mirrors the size, shape, and relative location on the other side.
1. Bilateral symmetry refers to organisms with body shapes that are mirror
images along a midline called the sagittal plane. The internal organs,
however, are not necessarily distributed symmetrically.
2. Radial symmetry is a symmetry in which the sides exhibit correspondence or
regularity of parts around a central axis. It is lacking left and right sides.
3. Spherical symmetry is a symmetry in which the shape of the body is spherical
and lack any axis. The body can be divided into two identical halves in any
plane that runs through the organism’s center.
Metamerism and Segmentation
Segmentation, also called metamerism, or metameric segmentation, in zoology,
the condition of being constructed of a linear series of repeating parts, each being a
metamere (body segment, or somite) and each being formed in sequence in the
embryo, from anterior to posterior.
Cephalization
Cephalization, the differentiation of the anterior (front) end of an organism into a
definite head. Considered an evolutionary advance, cephalization is accompanied by
a concentration of nervous tissue (cephalic ganglion or brain) and feeding
mechanisms in the head region that serves to integrate the activities of the nervous
system. Some groups of organisms show full cephalization, but because their bodies are
not divided into distinct trunks and heads, they cannot be said to possess a distinct
anatomical head.
Homology and Analogy
Homology is the similarity of the structure, physiology, or development of
different species of organisms based upon their descent from a common evolutionary
ancestor.
Analogy, on the other hand, is the similarity of function and superficial
resemblance of structures that have different origins. In many cases analogous
structures, or analogues, tend to become similar in appearance by a process termed
convergence.
Abdominal Regions and Quadrants
To promote clear communication, for instance about the location of a patient’s
abdominal pain or a suspicious mass, health care providers typically divide up the
cavity into either nine regions or four quadrants.
Membranes of the Anterior (Ventral) Body Cavity
A serous membrane (also referred to a serosa) is one of the thin membranes that
cover the walls and organs in the thoracic and abdominopelvic cavities. The parietal
layers of the membranes line the walls of the body cavity (pariet- refers to a cavity
wall). The visceral layer of the membrane covers the organs (the viscera). Between the
parietal and visceral layers is a very thin, fluid-filled serous space, or cavity.
There are three serous cavities and their associated membranes. The pleura is the
serous membrane that surrounds the lungs in the pleural cavity; the pericardium is the
serous membrane that surrounds the heart in the pericardial cavity; and the peritoneum
is the serous membrane that surrounds several organs in the abdominopelvic cavity. The
serous membranes form fluid-filled sacs, or cavities, that are meant to cushion and
reduce friction on internal organs when they move, such as when the lungs inflate or the
heart beats. Both the parietal and visceral serosa secrete the thin, slippery serous fluid
located within the serous cavities. The pleural cavity reduces friction between the lungs
and the body wall. Likewise, the pericardial cavity reduces friction between the heart
and the wall of the pericardium. The peritoneal cavity reduces friction between the
abdominal and pelvic organs and the body wall. Therefore, serous membranes provide
additional protection to the viscera they enclose by reducing friction that could lead to
inflammation of the organs
The Human Body Systems
The human body is composed of eleven distinct organ systems in the human
body. Assigning organs to organ systems can be imprecise since organs that “belong”
to one system can also have functions integral to another system. In fact, most organs
contribute to more than one system.
UNIVERSITY OF CALOOCAN CITY
Biglang Awa St., Corner Catleya St., EDSA, Caloocan City
COLLEGE OF EDUCATION
Anatomy and Physiology
SUBJECT CODE:
TOPIC OR LESSON:
WEEK:
SUB-TOPIC/S:
MBS 313
Phylum Chordata
3
1. The Characteristics of Chordates
2. The Characteristics of the Vertebrates
3. Classification of Chordates
OVERVIEW OF THE TOPIC
The phylum Chordata consists of animals with a flexible rod supporting their
dorsal or back sides. The phylum name derives from the Greek root word chordmeaning string. Most species within the phylum Chordata are vertebrates, or
animals with backbones (subphylum Vertebrata). Examples of vertebrate
chordates include fishes, amphibians, reptiles, birds, and mammals. A modern
human—one species of mammal—is a familiar example of a chordate. However,
we share this phylum with two groups of invertebrates as well. Tunicates
(subphylum Urochordata) and lancelets (subphylum Cephalochordata) are the
only invertebrate groups within the phylum Chordata. The Chordata is the animal
phylum with which everyone is most intimately familiar since it includes humans
and other vertebrates. However, not all chordates are vertebrates. All chordates
have similar features at some point in their life. Chordates other than craniates
include entirely aquatic forms. The strictly marine Urochordata or Tunicata are
commonly known as tunicates, sea squirts, and salps. There are roughly 1,600
species of urochordates; most are small solitary animals but some are colonial,
organisms. Nearly all are sessile as adults, but they have free-swimming, active
larval forms. Urochordates are unknown as fossils. Cephalochordata are also
known as amphioxus and lancelets. The group contains only about 20 species of
sand-burrowing marine creatures.
a.
b.
c.
Familiarize oneself to the different characteristics of chordates;
Identify the different classes of organisms under Phylum Chordata; and
Compare and contrast chordates from vertebrates and vice versa.
At the end of the lesson, students should be able to:
a.
b.
c.
enumerate the different characteristics of chordates;
cite the different characteristics of vertebrates; and
discuss the classification of chordates.
Phylum Chordata
The Phylum Chordata contains all of the animals that have a rod-like structure
used to give them support. In most cases this is the spine or backbone. Within Chordata
there are five classes of animals: fish, amphibians, reptiles, birds, and mammals. Three
dividing factors separate these classes:
A.
Regulation of body temperature: animals are either homeothermic (can regulate
their internal temperature so that it is kept at an optimum level) or poikilothermic
(cannot regulate their internal temperature, the environment affects how hot or cold
they are)
B.
Oxygen Absorption: the way in which oxygen is taken in from the air, which can
be through gills, the skin (amphibians), or lungs
C.
Reproduction: this factor is particularly varied. Animals can be oviparous (lay
eggs) or viviparous (birth live young). Fertilization can occur externally or internally. In
mammals, the mother produces milk for the young.
Characteristics of Chordata
Animals in the phylum Chordata share four key features that appear at some
stage during their development (often, only during embryogenesis).
1. Notochord - The chordates are named for the notochord: a flexible, rodshaped structure that is found in the embryonic stage of all chordates and
also in the adult stage of some chordate species. It is located between
the digestive tube and the nerve cord, providing skeletal support through
the length of the body. In some chordates, the notochord acts as the
primary axial support of the body throughout the animal’s lifetime.
In vertebrates, the notochord is present during embryonic development,
at which time it induces the development of the neural tube which serves
as a support for the developing embryonic body. The notochord,
however, is replaced by the vertebral column (spine) in most adult
vertebrates.
2.
Dorsal Hollow Nerve Cord - The dorsal hollow nerve cord derives
from ectoderm that rolls into a hollow tube during development. In
chordates, it is located dorsally (at the top of the animal) to the
notochord. In contrast to the chordates, other animal phyla are
characterized by solid nerve cords that are located either ventrally or
laterally. The nerve cord found in most chordate embryos develops into
the brain and spinal cord, which comprise the central nervous system.
3.
Pharyngeal Slits - are openings in the pharynx (the region just
posterior to the mouth) that extend to the outside environment. In
organisms that live in aquatic environments, pharyngeal slits allow for the
exit of water that enters the mouth during feeding. Some invertebrate
chordates use the pharyngeal slits to filter food out of the water that
enters the mouth. In vertebrate fishes, the pharyngeal slits develop into gill
arches, the bony or cartilaginous gill supports. In most terrestrial animals,
including mammals and birds, pharyngeal slits are present only during
embryonic development. In these animals, the pharyngeal slits develop
into the jaw and inner ear bones.
4.
Post-anal Tail - is a posterior elongation of the body, extending
beyond the anus. The tail contains skeletal elements and muscles, which
provide a source of locomotion in aquatic species. In some terrestrial
vertebrates, the tail also helps with balance, courting, and signaling when
danger is near. In humans and other apes, the post-anal tail is present
during embryonic development, but is vestigial as an adult.
Subphyla of Phylum Chordata
A.
Subphylum Vertebrata
This is the subphylum that we, and all other vertebrates, belong in.
Vertebrata is often referred to as Craniata because the organisms in this
subphylum have a head with a protective cranium, which most of us call a
skull. Vertebrates also have a brain encased in the skull, highly developed
internal organs, a closed circulatory system, and unique sensory and motor
cranial nerves. Fish, amphibians, reptiles, mammals, and birds are all part of his
subphylum, and thanks to the presence of bone or cartilage, their fossils are
easily found
B. Subphylum Cephalochordata
This literally means “head cords”. Cephalochordates are also called
Lancelets, and they are filter-feeding marine animals with elongated, small,
segmented, and soft bodies that make it difficult to find their fossils. They are
usually found in soft bottoms as they bury themselves in the substrate, exposing
their anterior part only (near the head) and using a row of tentacles to bring
food into their mouth. Cephalochordates resemble fish, as we can see in the
picture below, and swim like them, but they have no scales, backbone, limbs,
or brain. They outdo fish, however, in the number of pharyngeal gill slits that
they have.
C. Subphylum Urochordata
Meaning “tail cords”, these are also called Tunicates. This is another
subphylum whose organisms’ fossils are difficult to find, since the bodies have
no hard parts. It includes sea squirts and sea salps. These are barrel-shaped,
non-segmented filter-feeding marine animals. The larval stage usually has a tail
and is free-swimming, but it eventually attaches to a hard substrate and loses
the tail as it transforms into the adult form. By the time these organisms are
adults, they only display one characteristic of chordates, and that is
pharyngeal gill slits.
Classes Under Phylum Chordata
Class Mammalia
 They have four chambers in their hearts and use lungs for
breathing.
 They are warm-blooded animals.
 Most of them reproduce young except platypus who lay eggs.
 They are mostly terrestrial animals except a few who can fly and
live underwater.
 They have milk-producing glands for infants’ nourishment.
 These have two limbs for walking and other activities.
 Their skin has hair, external ears, and types of teeth in their jaws.
 They have different sex with internal fertilization and direct
development.
 They are mostly viviparous animals except for kangaroo, dolphins,
and blue whales.

Some examples are Platypus, Viviparous – Kangaroo, Flying fox,
Delphinus, etc.
Class Reptilia
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They are creepers and crawlers under this phylum.
They are mainly terrestrial with dry and confined skin cover.
These have epidemic scales or scutes on their skin.
Snakes and lizards at the time skin shed to remove the scales.
There is no ear opening and the Tympanum acts as an ear.
They have three chambers in their hearts and crocodiles have four.
Reptiles are cold-blooded animals.
They can lay eggs outside water as it has a hard covering.
The male and female sexes are different from internal fertilization.
They are oviparous animals with direct development.
Some examples are Turtle, Crocodile, Alligator, Wall lizard, Vipera,
etc.
Class Amphibia
 This class can easily survive in aquatic and terrestrial environments.
 They have moist skin without scales and eyelids for eyes. And the
ear is tympanum.
 They have a well-developed alimentary canal, urinary and
reproductive tracts that open in the exterior through the cloaca.
 Their heart has three chambers and is cold-blooded.
 The respiration process is by lungs, skin, and gills.
 The reproduction by different sexes and internal fertilization takes
place.
 They are oviparous animals with indirect development.
 Some examples are toads and frogs.
Class Aves
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They have four chambers in their hearts and use lungs for breathing.
All the birds are Aves.
They have feathers and can fly except flightless birds like Ostrich.
Their wings act as their forelimbs.
The scaled hind limbs enable them to walk, swim, and climb trees.
They only have oil glands at the tail, making the rest of the skin dry.
Their bones are hollow with air cavities.
The crop and gizzard are digestive tracts of them.
They come under warm-blooded animals.
They use lungs to respirate and air sacs near them.
These have different sexes with internal fertilization.
They are oviparous animals with direct development.
Some examples are Crow, Pigeon, Vulture, etc.
Class Pisces

They are the fishes under this class with scales and plates.
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A.
They are oviparous animals and use gills to respire.
These have a streamlined body and a muscular tail for movement.
They are cold-blooded animals with two chambers in the heart.
They have two types Chondrichthyes and Osteichthyes.
The Chondrichthyes have a cartilaginous skeleton.
The Osteichthyes have bony skeletons.
Chondrichthyes
 They are marine animals that have a cartilaginous
endoskeleton.
 They have a ventral mouth with a streamlined body.
 The notochord is present in them throughout life.
 They have separate gills without a cover.
 They have tough skin with placoid scales.
 These have very powerful jaws and are predaceous.
 They swim continuously to avoid drowning as there is no air
bladder.
 They have two chambers in their hearts and are coldblooded.
 Some of them have electric organs and a poison sting.
 They have different sexes with internal fertilization.
 Some examples are Scoliodon, Pristis, Trygon, etc.
B. Osteichthyes
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Fishes from fresh and marine water with bony
endoskeleton are under this subclass.
They have a streamlined body with a terminal mouth.
They have four pairs of gills with operculum cover on
each side.
These have cycloid scales on their skin.
To maintain buoyancy, they have an air bladder.
They have two chambers in the heart and are coldblooded animals.
The sexes are different from external fertilization.
They are mostly oviparous animals with direct
development.
Some examples are flying fish, Sea horse, Angelfish, etc.
Characteristics of Vertebrates
Vertebrates are members of the subphylum Vertebrata, under the phylum
Chordata and under the kingdom Animalia. All vertebrates have a similar anatomy and
morphology with the same qualifying characteristics: a notochord, a dorsal hollow
nerve cord, pharyngeal slits, and a post-anal tail. However, the subphylum Vertebrata is
distinguished from the phylum Chordata by the development of the notochord into a
bony backbone. Vertebrates include the amphibians, reptiles, mammals, and birds, as
well as the jawless fishes, bony fishes, sharks, and rays.
1. The Vertebral Column
 Vertebrates are defined by the presence of the vertebral
column. In vertebrates, the notochord develops into the
vertebral column or spine: a series of bony vertebrae each
separated by mobile discs. These vertebrae are always found
on the dorsal side of the animal.
2.
Central Nervous System
 Vertebrates are also the only members of Chordata to possess
a brain. In chordates, the central nervous system is based on a
hollow nerve tube that runs dorsal to the notochord along the
length of the animal. In vertebrates, the anterior end of the
nerve tube expands and differentiates into three brain vesicles.
3.
Closed Circulatory System
 is a type of circulatory systems in which blood is the circulatory
fluid, which circulates within closed vessels. Blood does not mix
with the interstitial fluid in a closed circulatory system. The closed
circulatory system comprises a heart, which pumps the blood
into the dorsal blood vessel. The dorsal blood vessel carries
blood to tissues and organs. The exchange of materials at
tissues occur via small vessels called capillaries found in the
tissue. The blood with wastes produced in the metabolism of
tissues is transported back into the heart by the ventral blood
vessel.
NOTE: Vertebrates and Chordates share similar characteristics, but Vertebrates are
organisms that possess a backbone or vertebral column that house the spinal cord.
CHORDATES
Chordates refer to an animal phylum that
contains a notochord and a dorsally situated
central nervous system.
Chordates possess a notochord at some point of
their life.
Invertebrate chordates do not have a vertebral
column.
Vertebrates, urochordates, and
cephalochordates are examples of chordates.
Starfish (Chordate, Invertebrate)
VERTEBRATES
Vertebrates refer to a large
group of animals, which consist of
a backbone.
Vertebrates possess a notochord
as well as a brain case.
Vertebrates have a vertebral
column surrounding the nerve
cord.
Mammals, birds, reptiles,
amphibians, and fish are
examples of vertebrates.
Lionfish (Chordate, Vertebrate)
UNIVERSITY OF CALOOCAN CITY
Biglang Awa St., Corner Catleya St., EDSA, Caloocan City
COLLEGE OF EDUCATION
Anatomy and Physiology
SUBJECT CODE:
TOPIC OR LESSON:
WEEK:
SUB-TOPIC/S:
MBS 313
The Human Skeletal System
4
1. The Importance and Function of the Skeletal System
2. The Anterior and Posterior Skeleton
3. The Appendicular Skeleton
OVERVIEW OF THE TOPIC
The supporting structure of the body is the framework of joined bones that
we refer to as skeleton. It enables us to stand erect, to move in our environment,
even sitting, walking , picking up a pencil, and taking a breath all involve the
skeletal system. Without the skeletal system, there would be no rigid framework to
support the soft tissues of the body and no system of joints and levers to allow the
body to move. The word skeleton is derived from the Greek word meaning dried.
The skeletal system is consists of bones, as well as their associated connective
tissues which includes cartilage, tendon, and ligament. It is closely related to the
Muscular system. Though the bones appear to be “dead” due to its stone-like
appearance, it is indeed composed of living tissues together with mineral salts like
calcium phosphate which is embedded in the inorganic matrix of the bone tissue.
Leonardo da Vinci was the first to correctly illustrate the Human Skeletal System
with 206 bones during the Renaissance period.
a.
b.
c.
Identify the different parts and function of the Human Skeletal System.
Compare the Axial Skeleton to Appendicular Skeleton and vice versa.
Discuss the importance of bones in our body.
At the end of the lesson, students should be able to:
a.
identify the importance and function of the skeletal system;
b.
and
c.
enumerate the different bones found in the anterior and posterior skeleton;
cite the different bones found on the appendicular portion of the skeleton.
The Human Skeletal System
The skeletal system is the body system composed of bones and cartilage and
performs the following critical functions for the human body:
1. Support. The skeleton serves as the structural framework for the body by
supporting soft tissues and providing attachment points for the tendons of
most skeletal muscles.
2. Protection. The skeleton protects the most important internal organs from injury.
For example, cranial bones protect the brain, and the rib cage protects the
heart and lungs.
3. Assistance in movement. Most skeletal muscles attach to bones; when they
contract, they pull on bones to produce movement.
4. Mineral homeostasis (storage and release). Bone tissue makes up about 18%
of the weight of the human body. It stores several minerals, especially calcium
and phosphorus, which contribute to the strength of bone. Bone tissue stores
about 99% of the body’s calcium.
5. Blood cell production. Within certain bones, a connective tissue called red
bone marrow produces red blood cells, white blood cells, and platelets, a
process called hemopoiesis. Red bone marrow consists of developing blood
cells, adipocytes, fibroblasts, and macrophages within a network of reticular
fibers.
6. Triglyceride storage. Yellow bone marrow consists mainly of adipose cells,
which store triglycerides. The stored triglycerides are a potential chemical
energy reserve.
Classification of Bones
A. Long Bones - A long bone is one that is cylindrical in shape, being
longer than it is wide. Keep in mind, however, that the term describes
the shape of a bone, not its size. Long bones are found in the arms
(humerus, ulna, radius) and legs (femur, tibia, fibula), as well as in the
fingers (metacarpals, phalanges) and toes (metatarsals, phalanges).
Long bones function as levers; they move when muscles contract.
B. Short Bones - A short bone is one that is cube-like in shape, being
approximately equal in length, width, and thickness. The only short
bones in the human skeleton are in the carpals of the wrists and the
tarsals of the ankles. Short bones provide stability and support as well
as some limited motion.
C. Flat Bones - The term “ flat bone” is somewhat of a misnomer because,
although a flat bone is typically thin, it is also often curved. Examples
include the cranial (skull) bones, the scapulae (shoulder blades), the
sternum (breastbone), and the ribs. Flat bones serve as points of
attachment for muscles and often protect internal organs.
D. Irregular Bones - An irregular bone is one that does not have any easily
characterized shape and therefore does not fit any other
classification. These bones tend to have more complex shapes, like the
vertebrae that support the spinal cord and protect it from compressive
forces. Many facial bones, particularly the ones containing sinuses, are
classified as irregular bones.
E. Sesamoid Bones - A sesamoid bone is a small, round bone that, as the
name suggests, is shaped like a sesame seed. These bones form in
tendons (the sheaths of tissue that connect bones to muscles) where a
great deal of pressure is generated in a joint. The sesamoid bones
protect tendons by helping them overcome compressive forces.
Sesamoid bones vary in number and placement from person to person
but are typically found in tendons associated with the feet, hands, and
knees. The patellae are the only sesamoid bones found in common
with every person.
Parts of the Bone
A long bone has two parts: the diaphysis and the epiphysis. The diaphysis is the
tubular shaft that runs between the proximal and distal ends of the bone. The hollow
region in the diaphysis is called the medullary cavity, which is filled with yellow marrow.
The walls of the diaphysis are composed of dense and hard compact bone.
The wider section at each end of the bone is called the epiphysis, which is
filled with spongy bone. Red marrow fills the spaces in the spongy bone. Each epiphysis
meets the diaphysis at the metaphysis, the narrow area that contains the epiphyseal
plate (growth plate), a layer of hyaline (transparent) cartilage in a growing bone. When
the bone stops growing in early adulthood (approximately 18–21 years), the cartilage is
replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal line.
The medullary cavity has a delicate membranous lining called the endosteum
(end- = “inside”; oste- = “bone”), where bone growth, repair, and remodeling occur. The
outer surface of the bone is covered with a fibrous membrane called the periosteum
(peri- = “around” or “surrounding”). The periosteum contains blood vessels, nerves, and
lymphatic vessels that nourish compact bone. Tendons and ligaments also attach to
bones at the periosteum. The periosteum covers the entire outer surface except where
the epiphyses meet other bones to form joints. In this region, the epiphyses are covered
with articular cartilage, a thin layer of cartilage that reduces friction and acts as a shock
absorber.
Bone Cell and Tissue
Bone contains a relatively small number of cells entrenched in a matrix of
collagen fibers that provide a surface for inorganic salt crystals to adhere. These salt
crystals form when calcium phosphate and calcium carbonate combine to create
hydroxyapatite, which incorporates other inorganic salts like magnesium hydroxide,
fluoride, and sulfate as it crystallizes, or calcifies (Calcification), on the collagen fibers.
The hydroxyapatite crystals give bones their hardness and strength, while the collagen
fibers give them flexibility so that they are not brittle.
Types of Bone Cells
1. Osteoprogenitor cells are unspecialized bone stem cells derived from
mesenchyme, the tissue from which almost all connective tissues are
formed. They are the only bone cells to undergo cell division; the
resulting cells develop into osteoblasts. Osteoprogenitor cells are found
along the inner portion of the periosteum, in the endosteum, and in
the canals within bone that contain blood vessels.
2. Osteoblasts are bone-building cells. They synthesize and secrete
collagen fibers and other organic components needed to build the
extracellular matrix of bone tissue, and they initiate calcification. As
osteoblasts surround themselves with extracellular matrix, they become
trapped in their secretions and become osteocytes.
3. Osteocytes, mature bone cells, are the main cells in bone tissue and
maintain its daily metabolism, such as the exchange of nutrients and
wastes with the blood. Like osteoblasts, osteocytes do not undergo cell
division.
4. Osteoclasts are huge cells derived from the fusion of as many as 50
monocytes (a type of white blood cell) and are concentrated in the
endosteum. On the side of the cell that faces the bone surface, the
osteoclast’s plasma membrane is deeply folded into a ruffled border.
Note:
The ending -blast in the name of a bone cell or any other connective tissue cell means
that the cell secretes extracellular matrix. The ending -cyte in the name of a bone cell
or any other tissue cell means that the cell maintains and monitors the tissue.
Compact and Spongy Bone
The differences between compact and spongy bone are best explored via their
histology. Most bones contain compact and spongy osseous tissue, but their distribution
and concentration vary based on the bone’s overall function. Compact bone is dense
so that it can withstand compressive forces, while spongy (cancellous) bone has open
spaces and supports shifts in weight distribution.
Compact bone is the denser, stronger of the two types of bone tissue. It can be
found under the periosteum and in the diaphysis of long bones, where it provides
support and protection.
Spongy bone, also known as cancellous bone, contains osteocytes housed in
lacunae, but they are not arranged in concentric circles. Instead, the lacunae and
osteocytes are found in a lattice-like network of matrix spikes called trabeculae. The
trabeculae may appear to be a random network, but each trabecula forms along lines
of stress to provide strength to the bone. The spaces of the trabeculated network
provide balance to the dense and heavy compact bone by making bones lighter so
that muscles can move them more easily. In addition, the spaces in some spongy
bones contain red marrow, protected by the trabeculae, where hematopoiesis
occurs.
Divisions of the Skeletal System
The skeleton is subdivided into two major divisions—the axial and appendicular.
The axial skeleton forms the vertical, central axis of the body and includes all bones of
the head, neck, chest, and back. It serves to protect the brain, spinal cord, heart, and
lungs. It also serves as the attachment site for muscles that move the head, neck, and
back, and for muscles that act across the shoulder and hip joints to move their
corresponding limbs.
The axial skeleton of the adult consists of 80 bones, including the skull, the
vertebral column, and the thoracic cage. The skull is formed by 22 bones. Also
associated with the head are an additional seven bones, including the hyoid bone and
the ear ossicles (three small bones found in each middle ear). The vertebral column
consists of 24 bones, each called a vertebra, plus the sacrum and coccyx. The thoracic
cage includes the 12 pairs of ribs, and the sternum, the flattened of the anterior chest.
Axial Skeleton
The Skull
The skull is the bony framework of the head. The bones of the skull are grouped
into two categories: cranial bones and facial bones. The cranial bones (crani- brain
case) form the cranial cavity, which encloses and protects the brain. The eight cranial
bones are the frontal bone, two parietal bones, two temporal bones, the occipital
bone, the sphenoid bone, and the ethmoid bone. Fourteen facial bones form the face:
two nasal bones, two maxillae, two zygomatic bones, the mandible, two lacrimal
bones, two palatine bones, two inferior nasal conchae, and the vomer.
Cranial Bones
The frontal bone forms the forehead (the anterior part of the cranium), the roofs
of the orbits (eye sockets), and most of the anterior part of the cranial floor. Soon after
birth, the left and right sides of the frontal bone are united by the metopic suture, which
usually disappears between the ages of six and eight.
The parietal bone forms most of the upper lateral side of the skull. These are paired bones,
with the right and left parietal bones joining together at the top of the skull. Each parietal
bone is also bounded anteriorly by the frontal bone, inferiorly by the temporal bone, and
posteriorly by the occipital bone.
The temporal bone forms the lower lateral side of the skull. Common wisdom has
it that the temporal bone (temporal = “time”) is so named because this area of the
head (the temple) is where hair typically first turns gray,
indicating the passage of time.
The occipital bone is the single bone that forms the posterior skull and posterior
base of the cranial cavity. On its outside surface, at the posterior midline, is a small
protrusion called the external occipital protuberance, which serves as an attachment site
for a ligament of the posterior neck. Lateral to either side of this bump is a superior nuchal
line (nuchal = “nape” or “posterior neck”). The nuchal lines represent the most superior
point at which muscles of the neck attach to the skull, with only the scalp covering the
skull above these lines. On the base of the skull, the occipital bone contains the large
opening of the foramen magnum, which allows for passage of the spinal cord as it exits
the skull. On either side of the foramen magnum is an oval-shaped occipital condyle.
These condyles form joints with the first cervical vertebra and thus support the skull on top
of the vertebral column.
The ethmoid bone is a delicate bone located in the anterior part of the cranial
floor medial to the orbits and is spongelike in appearance. It is anterior to the sphenoid
and posterior to the nasal bones. The ethmoid bone forms (1) part of the anterior portion
of the cranial floor; (2) the medial wall of the orbits; (3) the superior portion of the nasal
septum, a partition that divides the nasal cavity into right and left sides; and (4) most of
the superior sidewalls of the nasal cavity. The ethmoid bone is a major superior supporting
structure of the nasal cavity and forms an extensive surface area in the nasal cavity.
The Facial Bones
The paired nasal bones are small, flattened, rectangular-shaped
bones that form the bridge of the nose. These small bones protect the upper entry to the
nasal cavity and provide attachment for a couple of thin muscles of facial expression.
The paired lacrimal bones are thin and roughly resemble a fingernail in size and
shape. These bones, the smallest bones of the face, are posterior and lateral to the nasal
bones and form a part of the medial wall of each orbit.
The two L-shaped palatine bones form the posterior portion of the hard palate,
part of the floor and lateral wall of the nasal cavity, and a small portion of the floors of
the orbits.
The two inferior nasal conchae, which are inferior to the middle nasal conchae of
the ethmoid bone, are separate bones, not part of the ethmoid bone. These scroll-like
bones form a part of the inferior lateral wall of the nasal cavity and project into the nasal
cavity.
The vomer is a roughly triangular bone on the floor of the nasal cavity that
articulates superiorly with the perpendicular plate of the ethmoid bone and sphenoid
bone and inferiorly with both the maxillae and palatine bones along the midline.
The paired maxillae unite to form the upper jawbone. They articulate with every
bone of the face except the mandible (lower jawbone). The maxillae form part of the
floors of the orbits, part of the lateral walls and floor of the nasal cavity, and most of the
hard palate.
The two zygomatic bones, commonly called cheekbones, form the prominences
of the cheeks and part of the lateral wall and floor of each orbit.
The mandible, or lower jawbone, is the largest, strongest facial bone. It is the only
movable skull bone (other than the auditory ossicles, the small bones of the ear).
Hyoid Bone
The single hyoid bone ( U-shaped) is a unique component of the axial skeleton
because it does not articulate with any other bone. Rather, it is suspended from the
styloid processes of the temporal bones by ligaments and muscles. Located in the
anterior neck between the mandible and larynx, the hyoid bone supports the tongue,
providing attachment sites for some tongue muscles and for muscles of the neck and
pharynx. The hyoid bone consists of a horizontal body and paired projections called the
lesser horns and the greater horns. Muscles and ligaments attach to the body and these
paired projections.
The Vertebral Column
The vertebral column, also called the spine, backbone, or spinal column, makes up about
two-fifths of your total height and is composed of a series of bones called vertebrae. The
vertebral column, the sternum, and the ribs form the skeleton of the trunk of the body.
The vertebral column consists of bone and connective tissue; the spinal cord that it
surrounds and protects consists of nervous and
connective tissues.
The total number of vertebrae during early development is 33. As a child grows,
several vertebrae in the sacral and coccygeal regions fuse. As a result, the adult vertebral
column typically contains 26 vertebrae. These are distributed as follows:
A.
7 cervical vertebrae (cervic - neck) in the neck region.
B.
12 thoracic vertebrae (thorax - chest) posterior to the thoracic cavity.
C.
5 lumbar vertebrae (lumb - loin) supporting the lower back.
D.
1 sacrum (SAˉ-krum - sacred bone) consisting of five fused sacral vertebrae.
E.
1 coccyx (KOK-siks - cuckoo, because the shape resembles the bill of a cuckoo
bird) usually consisting of four fused coccygeal vertebrae.
NOTE:
The cervical, thoracic, and lumbar vertebrae are movable, but the sacrum and coccyx
are not.
Regional Modifications of the Vertebrae
Cervical vertebrae have a small body, reflecting the fact that they carry the least
amount of body weight. Cervical vertebrae usually have a bifid (Y-shaped) spinous
process. The spinous processes of the C3–C6 vertebrae are short, but the spine of C7 is
much longer. The first and second cervical vertebrae are further modified, giving each a
distinctive appearance. The first cervical (C1) vertebra is also called the atlas, because
this is the vertebra that supports the skull on top of the vertebral column. The second
cervical (C2) vertebra is called the axis, because it serves as the axis for rotation when
turning the head toward the right or left.
The bodies of the thoracic vertebrae are larger than those of cervical vertebrae.
The characteristic feature for a typical midthoracic vertebra is the spinous process,
which is long and has a pronounced downward angle that causes it to overlap the
next inferior vertebra.
The lumbar vertebrae carry the greatest amount of body weight and are thus
characterized by the large size and thickness of the vertebral body. They have short
transverse processes and a short, blunt spinous process that projects posteriorly.
The sacrum is a triangular-shaped bone that is thick and wide across its superior
base where it is weight bearing and then tapers down to an inferior, non-weight
bearing apex. The coccyx, or tailbone, is derived from the fusion of four very small
coccygeal vertebrae. It articulates with the inferior tip of the sacrum. It is not weight
bearing in the standing position, but may receive some body weight when sitting.
The Thoracic Bones
The thoracic cage (rib cage) forms the thorax (chest) portion of the body. It
consists of the 12 pairs of ribs with their costal cartilages and the sternum. The ribs are
anchored posteriorly to the 12 thoracic vertebrae (T1–T12). The thoracic cage protects
the heart and lungs.
The sternum, or breastbone, is a flat, narrow bone located in the center of the
anterior thoracic wall that measures about 15 cm (6 in.) in length and consists of three
parts. The superior part is the manubrium ; the middle and largest part is the body; and
the inferior, smallest part is the xiphoid process.
Each rib is a curved, flattened bone that contributes to the wall of the thorax.
The ribs articulate posteriorly with the T1–T12 thoracic vertebrae, and most attach
anteriorly via their costal cartilages to the sternum. There are 12 pairs of ribs. The ribs are
numbered 1–12 in accordance with the thoracic vertebrae.
Appendicular Bones
The appendicular skeleton consists of the pectoral and pelvic girdles, the limb
bones, and the bones of the hands and feet.
The human body has two pectoral (shoulder) girdles that attach the bones of
the upper limbs to the axial skeleton. Each of the two pectoral girdles consists of a
clavicle and a scapula. The clavicle is the anterior bone and articulates with the
manubrium of the sternum at the sternoclavicular joint. The scapula articulates with the
clavicle at the acromioclavicular joint and with the humerus at the glenohumeral
(shoulder) joint.
Each upper limb (upper extremity) has 30 bones in three locations—(1) the
humerus in the arm; (2) the ulna and radius in the forearm; and (3) the 8 carpals in the
carpus (wrist), the 5 metacarpals in the metacarpus (palm), and the 14 phalanges
(bones of the digits) in the hand.
The pelvic girdle (hip girdle) is formed by a single bone, the hip bone or coxal
bone, which serves as the attachment point for each lower limb. Each hip bone, in turn,
is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral
column. The right and left hip bones also converge anteriorly to attach to each other.
The bony pelvis is the entire structure formed by the two hip bones, the sacrum, and,
attached inferiorly to the sacrum, the coccyx. Unlike the bones of the pectoral girdle,
which are highly mobile to enhance the range of upper limb movements, the bones of
the pelvis are strongly united to each other to form a largely immobile, weight-bearing
structure. This is important for stability because it enables the weight of the body to be
easily transferred laterally from the vertebral column, through the pelvic girdle and hip
joints, and into either lower limb whenever the other limb is not bearing weight. Thus, the
immobility of the pelvis provides a strong foundation for the upper body as it rests on top
of the mobile lower limbs.
Like the upper limb, the lower limb is divided into three regions. The thigh is that
portion of the lower limb located between the hip joint and knee joint. The leg is
specifically the region between the knee joint and the ankle joint. Distal to the ankle is
the foot. The lower limb contains 30 bones. These are the femur, patella, tibia, fibula, tarsal
bones, metatarsal bones, and phalanges. The femur is the single bone of the thigh. The
patella is the kneecap and articulates with the distal femur. The tibia is the larger, weightbearing bone located on the medial side of the leg, and the fibula is the thin bone of the
lateral leg. The bones of the foot are divided into three groups. The posterior portion of
the foot is formed by a group of seven bones, each of which is known as a tarsal bone,
whereas the mid-foot contains five elongated bones, each of which is a metatarsal bone.
The toes contain 14 small bones, each of which is a phalanx bone of the foot.
UNIVERSITY OF CALOOCAN CITY
Biglang Awa St., Corner Catleya St., EDSA, Caloocan City
COLLEGE OF EDUCATION
Anatomy and Physiology
SUBJECT CODE:
TOPIC OR LESSON:
WEEK:
SUB-TOPIC/S:
MBS 313
The Structure of the Bone
5
1. Bone Structure
2. Joints
3. Traumatic Fractures of the Bones
4. Repair of a Fracture
OVERVIEW OF THE TOPIC
There are two types of bone tissue: compact bone and spongy bone which
is also called as cancellous bone. In both types of bone tissues, the osteocyte is
the same but the arrangement on how blood supply reaches the bone cells is
different. The human bones undergo changes as a person age. Bones tend to
become brittle as a person gets older and various diseases affecting the Skeletal
System emerges in relation to age, health, and genetics. Furthermore, the bone,
cartilage, tendons, ligaments, and joints of the Skeletal System are made of
connective tissues.
a.
b.
c.
d.
At the end of this module, the students can;
Correctly identify the different structures of the bone;
Name the different kinds o joints and determine their location;
Cite different kinds of bone fracture; and
Explain how do fractured bones are repaired.
a.
b.
c.
d.
At the end of the lesson, students should be able to:
describe the structure of the bone;
identify the different kinds of joint and their location;
enumerate some traumatic fractures of the bones; and
discuss how can a fracture be repaired.
The Structure of the Bone
Compact Bone
Compact bone tissue contains few spaces and is the strongest form of bone tissue.
It is found beneath the periosteum of all bones and makes up the bulk of the diaphysis of
long bones. Compact bone tissue provides protection and support and resists the stresses
produced by weight and movement.
1. Osteon – the microscopic structural unit of compact bones. Also called as
Haversian System.
2. Haversian Canal – also called as Central Canal. Located at the center of each
osteon which contains blood vessels, nerves, and lymphatic vessels.
3. Volkmann’s Canal – also called as Perforating Canal. These are passageway
of blood vessels, nerves, and lymphatic vessels from the Central Canal to the
periosteum.
4. Concentric Lamella – are calcified matrix made of organic and inorganic
component of the bone that surrounds each Haversian Canal.
5. Lacunae – are small spaces between Concentric lamella where osteocytes
are found.
6. Canaliculi – are small channels that radiated from the lacunae to the Central
Canal.
7. Osteocytes – are mature bone cells and the main cells in bone tissue and
maintain its daily metabolism.
8. Interstitial Lamellae - are fragments of older osteons that have been partially
destroyed during bone rebuilding or growth.
9. Circumferential Lamellae – lamellae that are arranged in the entire inner and
outer shaft of long bone which are developed during bone formation. These
are classified as Outer Circumferential Lamellae which is deep to the
Periosteum and Inner Circumferential Lamellae which lines the Medullar
Cavity.
10. Perforating Fibers – also called as Sharpey’s Fibers. These are fibers that
connect the Outer Circumferential Lamellae to the periosteum.
Spongy Bone
In contrast to compact bone tissue, spongy bone tissue, also referred to as
trabecular or cancellous bone tissue, does not contain osteons. Spongy bone tissue is
always located in the interior of a bone, protected by a covering of compact bone.
1. Trabeculae – are lattice- like network of matrix spikes where lacunane and
osteocytes are found.
2. Red bone Marrow – found at macrosopic spaces of spongy bone responsible
for hematopeisis.
Spongy bone tissue is different from compact bone tissue in two respects. First,
spongy bone tissue is light, which reduces the overall weight of a bone. This reduction in
weight allows the bone to move more readily when pulled by a skeletal muscle. Second,
the trabeculae of spongy bone tissue support and protect the red bone marrow. Spongy
bone in the hip bones, ribs, sternum (breastbone), vertebrae, and the proximal ends of
the humerus and femur is the only site where red bone marrow is stored.
Joints
A joint, also called an articulation or arthrosis, is a point of contact between two
bones, between bone and cartilage, or between bone and teeth. When we say one
bone articulates with another bone, we mean that the bones form a joint.
Joints are classified structurally, based on their anatomical characteristics, and
functionally, based on the type of movement they permit.
The structural classification of joints is based on two criteria:
a.
the presence or absence of a space between the articulating
bones, called a synovial cavity, and
b.
the type of connective tissue that binds the bones together.
Structurally, joints are classified as one of the following types:
1. Fibrous joints - There is no synovial cavity, and the bones are held together
by dense irregular connective tissue that is rich in collagen fibers.
2. Cartilaginous joints - There is no synovial cavity, and the bones are held
together by cartilage.
3. Synovial joints - The bones forming the joint have a synovial cavity and are
united by the dense irregular connective tissue of an articular capsule,
and often by accessory ligaments.
The functional classification of joints relates to the degree of movement they permit.
Functionally, joints are classified as one of the following types:
1. Synarthrosis (together): An immovable joint. The plural is synarthroses.
2. Amphiarthrosis (on both sides): A slightly movable joint. The plural is
amphiarthroses.
3. Diarthrosis (movable joint): A freely movable joint. The plural is diarthroses. All
diarthroses are synovial joints. They have a variety of shapes and permit
several different types of movements.
Types of Fibrous Joints
a. A suture is a fibrous joint composed of a thin layer of dense irregular
connective tissue; sutures occur only between bones of the skull.
b. A gomphosis (fastened with bolts) is the specialized fibrous joint that anchors
the root of a tooth into its bony socket within the maxillary bone (upper jaw)
or mandible bone (lower jaw) of the skull. A gomphosis is also known as a
peg-andsocket joint.
c.
A syndesmosis (band or ligament) is a fibrous joint in which there is a greater
distance between the articulating surfaces and more dense irregular connective tissue
than in a suture. The dense irregular connective tissue is typically arranged as a bundle
(ligament), allowing the joint to permit limited movement
d. The interosseous membrane, which is a substantial sheet of dense irregular
connective tissue that binds neighboring long bones and permits slight
movement (amphiarthrosis). There are two principal interosseous membrane
joints in the human body. One occurs between the radius and ulna in the
forearm and the other occurs between the tibia and fibula in the leg.
Types of Cartilaginous Bones
a.
A synchondrosis (cartilage) is a cartilaginous joint in which the connecting
material is hyaline cartilage. An example of a synchondrosis is the epiphyseal (growth)
plate that connects the epiphysis and diaphysis of a growing bone.
b.
A symphysis (growing together) is a cartilaginous joint in which the ends of the
articulating bones are covered with hyaline cartilage, but a broad, flat disc of
fibrocartilage connects the bones. All symphyses occur in the midline of the body. The
pubic symphysis between the anterior surfaces of the hip bones is one example of a
symphysis. This type of joint is also found at the junction of the manubrium and body of
the sternum and at the intervertebral joints between the bodies of vertebrae.
Structure of Synovial Joints
Synovial joints have certain characteristics that distinguish them from other joints.
The unique characteristic of a synovial joint is the presence of a space called a synovial
cavity or joint cavity between the articulating bones. Because the synovial
cavity allows considerable movement at a joint, all synovial joints are classified
functionally as freely movable (diarthroses). The bones at a synovial joint are covered
by a layer of hyaline cartilage called articular cartilage. The cartilage covers the
articulating surfaces of the bones with a smooth, slippery surface but does not bind
them together. Articular cartilage reduces friction between bones in the joint during
movement and helps to absorb shock. A sleeve- like articular capsule or joint capsule
surrounds a synovial joint, encloses the synovial cavity, and unites the articulating
bones. The articular capsule is composed of two layers, an outer fibrous membrane,
and an inner synovial membrane. The fibrous membrane usually consists of dense
irregular connective tissue (mostly collagen fibers) that attaches to the periosteum of
the articulating bones.
The synovial membrane secretes synovial fluid, a viscous, clear or pale-yellow
fluid named for its similarity in appearance and consistency to uncooked egg white.
Synovial fluid consists of hyaluronic acid secreted by synovial cells in the synovial
membrane and interstitial fluid filtered from blood plasma. It forms a thin film over the
surfaces within the articular capsule. Its functions include reducing friction by lubricating
the joint, absorbing shocks, and supplying oxygen and nutrients to and removing
carbon dioxide and metabolic wastes from the chondrocytes within articular cartilage.
Synovial fluid also contains phagocytic cells that remove microbes and the debris that
results from normal wear and tear in the joint. When a synovial joint is immobile for a
time, the fluid becomes quite viscous (gel-like), but as joint movement increases, the
fluid becomes less viscous.
Accessory Ligaments, Articular Discs, and Labra
1. Extracapsular ligaments lie outside the articular capsule. Examples are the
fibular and tibial collateral ligaments of the knee joint.
2. Intracapsular ligaments occur within the articular capsule but are excluded
from the synovial cavity by folds of the synovial membrane.
3. Articular Disc or Menisci – found inside some synovial joints, such as the knee,
are crescent-shaped pads of fibrocartilage that lie between the articular
surfaces of the bones and are attached to the fibrous capsule. The functions
of the menisci are not completely understood but are known to include the
following:
a. shock absorption;
b. a better fit between articulating bony surfaces;
c. providing adaptable surfaces for combined
movements;
d. weight distribution over a greater contact surface;
and
e. distribution of synovial lubricant across the articular
surfaces of the joint
4. Labra - prominent in the ball and-socket joints of the shoulder and hip, is
the fibrocartilaginous lip that extends from the edge of the joint socket. The
labrum helps deepen the joint socket and increases the area of contact
between the socket and the ball-like surface of the head of the humerus or
femur.
Bursae and Tendon Sheaths
The various movements of the body create friction between moving parts. Saclike
structures called bursae are strategically situated to alleviate friction in some joints, such
as the shoulder and knee joints. Bursae are not strictly part of synovial joints, but they do
resemble joint capsules because their walls consist of an outer fibrous membrane of thin,
dense connective tissue lined by a synovial membrane. They are filled with a small
amount of fluid that is similar to synovial fluid. Bursae can be located between the skin
and bones, tendons and bones, muscles and bones, or ligaments and bones. The fluidfilled bursal sacs cushion the movement of these body parts against one another. Tendon
sheaths or synovial sheaths are tubelike bursae; they wrap around certain tendons that
experience considerable friction as they pass through tunnels formed by connective
tissue and bone. The inner layer of a tendon sheath, the visceral layer, is attached to the
surface of the tendon. The outer layer, known as the parietal layer, is attached to bone.
Types of Synovial Joints
A.
Plane Joint (gliding joint) - the articulating surfaces of the bones are flat or slightly
curved and of approximately the same size, which allows the bones to slide against
each other. The motion at this type of joint is usually small and tightly constrained by
surrounding ligaments. Based only on their shape, plane joints can allow multiple
movements, including rotation. Thus, plane joints can be functionally classified as a
multiaxial joint.
B.
Hinge Joint - the convex end of one bone articulates with the concave end of
the adjoining bone. This type of joint allows only for bending and straightening motions
along a single axis, and thus hinge joints are functionally classified as uniaxial joints.
C. Pivot Joint - a rounded portion of a bone is enclosed within a ring formed
partially by the articulation with another bone and partially by a ligament.
The bone rotates within this ring.
D.
Condyloid Joint (ellipsoid joint)- the shallow depression at the end of one bone
articulates with a rounded structure from an adjacent bone or bones. The knuckle
(metacarpophalangeal) joints of the hand between the distal end of a metacarpal
bone and the proximal phalanx bone are condyloid joints.
E. Saddle Joint - both of the articulating surfaces for the bones have a saddle
shape, which is concave in one direction and convex in the other. This allows
the two bones to fit together like a rider sitting on a saddle. Saddle joints are
functionally classified as biaxial joints.
F.
Ball and Socket Joint – joint with the greatest range of motion. At these joints, the
rounded head of one bone (the ball) fits into the concave articulation (the socket) of
the adjacent bone. The hip joint and the glenohumeral (shoulder) joint are the only
ball-and-socket joints of the body. At the hip joint, the head of the femur articulates
with the acetabulum of the hip bone, and at the shoulder joint, the head of the
humerus articulates with the glenoid cavity of the scapula.
Kinds of Fracture
A fracture is a broken bone. It will heal whether or not a physician resets it in its
anatomical position. If the bone is not reset correctly, the healing process will keep the
bone in its deformed position. When a broken bone is manipulated and set into its
natural position without surgery, the procedure is called a closed reduction. Open
reduction requires surgery to expose the fracture and reset the bone. While some
fractures can be minor, others are quite severe and result in grave complications.
1. Transverse – occurs straight across the long axis of the bone.
2. Oblique – occurs at an angle that is not 90°.
3. Spiral – bone segments are pulled apart because of twisting motion.
4. Comminuted – several breaks resulted to many small pieces between two
large segments.
5. Impacted – one fragment is impacted to the other, usually a result of
compression.
6. Greenstick – a partial fracture in which only one side of the bone is broken.
7. Open or Compound - a fracture in which at least one end of the broken
bone tears through the skin; carries a high risk of infection.
8. Closed or Simple - a fracture in which the skin remains intact.
Repair of Bone Fracture
When a bone breaks, blood flows from any vessel torn by the fracture. These
vessels could be in the periosteum, osteons, and/or medullary cavity. The blood begins
to clot, and about six to eight hours after the fracture, the clotting blood has formed a
fracture hematoma. The disruption of blood flow to the bone results in the death of
bone cells around the fracture.
The healing of a bone fracture follows a series of progressive steps: (a) A
fracture hematoma forms. (b) Internal and external calli form. (c) Cartilage of the calli is
replaced by trabecular bone.(d) Remodeling occurs.
Repair of Bone Fracture
1. Reactive phase. This phase is an early inflammatory phase. Blood vessels
crossing the fracture line are broken. As blood leaks from the torn ends of the
vessels, a mass of blood (usually clotted) forms around the site of the fracture.
This mass of blood, called a fracture hematoma, usually forms 6 to 8 hours
after the injury. Because the circulation of blood stops at the site where the
fracture hematoma forms, nearby bone cells die.
2. Reparative phase: Fibrocartilaginous callus formation. Blood vessels grow into
the fracture hematoma and phagocytes begin to clean up dead bone cells.
Fibroblasts from the periosteum invade the fracture site and produce
collagen fibers. In addition, cells from the periosteum develop into
chondroblasts and begin to produce fibrocartilage in this region. These
events lead to the development of a fibrocartilaginous callus, a mass of
repair tissue consisting of collagen fibers and cartilage that bridges the
broken ends of the bone. Formation of the fibrocartilaginous callus takes
about 3 weeks.
3. Reparative phase: Bony callus formation. In areas closer to well-vascularized
healthy bone tissue, osteoprogenitor cells develop into osteoblasts, which
begin to produce spongy bone trabeculae. The trabeculae join living and
dead portions of the original bone fragments. In time, the fibrocartilage is
converted to spongy bone, and the callus is then referred to as a bony (hard)
callus. The bony callus lasts about 3 to 4 months.
4. Bone remodeling phase. The final phase of fracture repair is bone remodeling
of the callus. Dead portions of the original fragments of broken bone are
gradually resorbed by osteoclasts. Compact bone replaces spongy bone
around the periphery of the fracture. Sometimes, the repair process is so
thorough that the fracture line is undetectable, even in a radiograph (x-ray).
However, a thickened area on the surface of the bone remains as evidence
of a healed fracture.
UNIVERSITY OF CALOOCAN CITY
Biglang Awa St., Corner Catleya St., EDSA, Caloocan City
COLLEGE OF EDUCATION
Anatomy and Physiology
SUBJECT CODE:
TOPIC OR LESSON:
WEEK:
SUB-TOPIC/S:
MBS 313
Nervous System
6
1. Anatomy of the Nervous System
2. Atlas of the Human Brain
3. The Eye and the Ear
OVERVIEW OF THE TOPIC
The nervous system has this very important objective: to keep controlled
conditions within limits that maintain life. The nervous system regulates body
activities by responding rapidly using nerve impulses. The nervous system is also
responsible for our perceptions, behaviors, and memories, and it initiates all
voluntary movements. With a mass of only 2 kg (4.5 lb), about 3% of the total body
weight, the nervous system is one of the smallest and yet the most complex of the
11 body systems. This intricate network of billions of neurons and even more
neuroglia is organized into two main subdivisions: the central nervous system and
the peripheral nervous system. The central nervous system (CNS) is the brain and
spinal cord, and the peripheral nervous system (PNS) is everything else.
The brain is contained within the cranial cavity of the skull, and the spinal
cord is contained within the vertebral cavity of the vertebral column. It is a bit of
an oversimplification to say that the CNS is what is inside these two cavities and
the peripheral nervous system is outside of them, but that is one way to start to
think about it. There are some elements of the peripheral nervous system that are
within the cranial or vertebral cavities. The peripheral nervous system is so named
because it is on the periphery—meaning beyond the brain and spinal cord.
Depending on different aspects of the nervous system, the dividing line between
central and peripheral is not necessarily universal.
At the end of this module, the students can;
a.
Correctly identify the different structures of the brain and spinal cord.
b.
Cite the differences between Central Nervous System and Peripheral Nervous
System.
c.
Explain the interaction between our ears and eyes as sense organs to our brain.
a.
b.
c.
At the end of the lesson, students should be able to:
describe the anatomy of the nervous system;
discuss the atlas of the human brain; and
describe the eye & the ear.
Anatomy of the Nervous System
Central Nervous System
The central nervous system (CNS) consists of the brain and spinal cord. The brain
is the part of the CNS that is in the skull and contains about 85 billion neurons. The spinal
cord is connected to the brain through the foramen magnum of the occipital bone
and is encircled by the bones of the vertebral column. The spinal cord contains about
100 million neurons. The CNS processes many kinds of incoming sensory information. It is
also the source of thoughts, emotions, and memories. Most signals that stimulate
muscles to contract and glands to secrete originate in the CNS.
Peripheral Nervous System
The peripheral nervous system (PNS)consists of all nervous tissue outside the CNS.
Components of the PNS include nerves, ganglia, enteric plexuses, and sensory
receptors.
a. Nerve is a bundle of hundreds to thousands of axons plus associated
connective tissue and blood vessels that lies outside the brain and spinal
cord. Twelve pairs of cranial nerves emerge from the brain and thirty-one
pairs of spinal nerves emerge from the spinal cord. Each nerve follows a
defined path and serves a specific region of the body.
b. Ganglia are small masses of nervous tissue, consisting primarily of neuron
cell bodies, that are located outside of the brain and spinal cord. Ganglia
are closely associated with cranial and spinal nerves.
c. Enteric plexuses are extensive networks of neurons located in the walls of
organs of the gastrointestinal tract. The neurons of these plexuses help
regulate the digestive system.
d. Sensory receptor refers to a structure of the nervous system that monitors
changes in the external or internal environment. Examples of sensory
receptors include touch receptors in the skin, photoreceptors in the eye, and
olfactory receptors in the nose.
The PNS is divided into a somatic nervous system, an autonomic nervous system
(ANS) and an enteric nervous system (ENS).
 The SNS consists of (1) sensory neurons that convey information to the CNS
from somatic receptors in the head, body wall, and limbs and from
receptors for the special senses of vision, hearing, taste, and smell, and (2)
motor neurons that conduct impulses from the CNS to skeletal muscles
only. Because these motor responses can be consciously controlled, the
action of this part of the PNS is voluntary.
 The ANS consists of (1) sensory neurons that convey information to the
CNS from autonomic sensory receptors, located primarily in visceral
organs such as the stomach and lungs, and (2) motor neurons that
conduct nerve impulses from the CNS to smooth muscle, cardiac muscle,

and glands. Because its motor responses are not normally under
conscious control, the action of the ANS is involuntary. The motor part of
the ANS consists of two branches, the sympathetic division and the
parasympathetic division. With a few exceptions, effectors receive nerves
from both divisions, and usually the two divisions have opposing actions.
For example, sympathetic neurons increase heart rate, and
parasympathetic neurons slow it down. In general, the sympathetic
division helps support exercise or emergency actions, the “fight-or-flight”
responses, and the parasympathetic division takes care of “rest-anddigest” activities.
The operation of the ENS, the “brain of the gut,” is involuntary. The ENS
consists of over 100 million neurons in enteric plexuses that extend most of
the length of the gastrointestinal (GI) tract. Many of the neurons of the
enteric plexuses function independently of the ANS and CNS to some
extent, although they also communicate with the CNS via sympathetic
and parasympathetic neurons. Sensory neurons of the ENS monitor
chemical changes within the GI tract as well as the stretching of its walls.
Enteric motor neurons govern contractions of GI tract smooth muscle to
propel food through the GI tract, secretions of GI tract organs (such as
acid from the stomach), and activities of GI tract endocrine cells, which
secrete hormones.
Functions of the Nervous System
A. Sensory function. Sensory receptors detect internal stimuli, such as an
increase in blood pressure, or external stimuli (for example, a raindrop landing
on your arm). This sensory information is then carried into the brain and spinal
cord through cranial and spinal nerves.
B. Integrative function. The nervous system processes sensory information by
analyzing it and making decisions for appropriate responses—an activity
known as integration.
C. Motor function. Once sensory information is integrated, the nervous system
may elicit an appropriate motor response by activating effectors (muscles
and glands) through cranial and spinal nerves. Stimulation of the effectors
causes muscles to contract and glands to secrete.
Histology of the Nervous Tissue
Nervous tissue comprises two types of cells—neurons and neuroglia. These cells
combine in a variety of ways in different regions of the nervous system. In addition to
forming the complex processing networks within the brain and spinal cord, neurons also
connect all regions of the body to the brain and spinal cord. As highly specialized cells
capable of reaching great lengths and making extremely intricate connections with
other cells, neurons provide most of the unique functions of the nervous system, such as
sensing, thinking, remembering, controlling muscle activity, and regulating glandular
secretions. As a result of their specialization, most neurons have lost the ability to undergo
mitotic divisions. Neuroglia are smaller cells, but they greatly outnumber neurons,
perhaps by as much as 25 times. Neuroglia support, nourish, and protect neurons, and
maintain the interstitial fluid that bathes them. Unlike neurons, neuroglia continues to
divide throughout an individual’s lifetime. Both neurons and neuroglia differ structurally
depending on whether they are in the central nervous system or the peripheral nervous
system. These differences in structure correlate with the differences in function of the
central nervous system and the peripheral nervous system.
Neurons
Like muscle cells, neurons or nerve cells possess electrical excitability, the ability to
respond to a stimulus and convert it into an action potential. A stimulus is any change in
the environment that is strong enough to initiate an action potential. An action potential
(nerve impulse) is an electrical signal that propagates (travels) along the surface of the
membrane of a neuron. It begins and travels due to the movement of ions (such as
sodium and potassium) between interstitial fluid and the inside of a neuron through
specific ion channels in its plasma membrane. Once begun, a nerve impulse travels
rapidly and at a constant strength.
Parts of a Neuron
1. Cell body - also known as the perikaryon or soma, contains a nucleus
surrounded by cytoplasm that includes typical cellular organelles such
as lysosomes, mitochondria, and a Golgi complex. Neuronal cell bodies
also contain free ribosomes and prominent clusters of rough
endoplasmic reticulum, termed Nissl bodies. The ribosomes are the sites
of protein synthesis. Newly synthesized proteins produced by Nissl bodies
are used to replace cellular components, as material for growth of
neurons, and to regenerate damaged axons in the PNS. The
cytoskeleton includes both neurofibrils, composed of bundles of
intermediate filaments that provide the cell shape and support, and
microtubules, which assist in moving materials between the cell body
and axon. Aging neurons also contain lipofuscin, a pigment that occurs
as clumps of yellowish-brown granules in the cytoplasm. Lipofuscin is a
product of neuronal lysosomes that accumulates as the neuron ages
but does not seem to harm the neuron. A nerve fiber is a general term
for any neuronal process (extension) that emerges from the cell body of
a neuron. Most neurons have two kinds of processes: multiple dendrites
and a single axon.
2. Dendrites - are the receiving or input portions of a neuron. The plasma
membranes of dendrites (and cell bodies) contain numerous receptor
sites for binding chemical messengers from other cells. Dendrites usually
are short, tapering, and highly branched. In many neurons the dendrites
form a tree-shaped array of processes extending from the cell body.
Their cytoplasm contains Nissl bodies, mitochondria, and other
organelles.
3. Axon - The single axon of a neuron propagates nerve impulses toward
another neuron, a muscle fiber, or a gland cell. An axon is a long, thin,
cylindrical projection that often joins to the cell body at a cone-shaped
elevation called the axon hillock. The part of the axon closest to the
axon hillock is the initial segment. In most neurons, nerve impulses arise
at the junction of the axon hillock and the initial segment, an area
called the trigger zone, from which they travel along the axon to their
destination. An axon contains mitochondria, microtubules, and
neurofibrils. Because rough endoplasmic reticulum is not present,
protein synthesis does not occur in the axon. The cytoplasm of an axon,
called axoplasm, is surrounded by a plasma membrane known as the
axolemma. Along the length of an axon, side branches called axon
collaterals may branch off, typically at a right angle to the axon. The
axon and its collaterals end by dividing into many fine processes called
axon terminals or axon telodendrion.
Types of Neurons
1. Multipolar neurons usually have several dendrites and one axon. Most neurons
in the brain and spinal cord are of this type, as well as all motor neurons.
2. Bipolar neurons have one main dendrite and one axon. They are found in the
retina of the eye, the inner ear, and the olfactory area (olfact- to smell) of the
brain.
3. Unipolar neurons have dendrites and one axon that are fused together to form
a continuous process that emerges from the cell body. These neurons are more
appropriately called pseudo-unipolar neurons because they begin in the
embryo as bipolar neurons. During development, the dendrites and axon fuse
together and become a single process. The dendrites of most unipolar neurons
function as sensory receptors that detect a sensory stimulus such as touch,
pressure, pain, or thermal stimuli. The trigger zone for nerve impulses in a
unipolar neuron is at the junction of the dendrites and axon. The impulses then
propagate toward the synaptic end bulbs. The cell bodies of most unipolar
neurons are in the ganglia of spinal and cranial nerves.
Sensory Receptors (Dendrites) of Unipolar Neuron
a.
A corpuscle of touch is a touch receptor that consists of a mass of dendrites
enclosed by a capsule of connective tissue.
b.
A type I cutaneous mechanoreceptor is a touch receptor that consists of free
nerve endings (bare dendrites) that contact tactile epithelial cells of the stratum basale
of the skin.
c.
A lamellated corpuscle is a pressure receptor composed of a multilayered
connective tissue capsule that encloses a dendrite.
d.
A nociceptor is a pain receptor that consists of free nerve endings (bare
dendrites).
Functional Classifications of Neurons
1. Sensory or afferent neurons (af- toward) either contain sensory receptors at
their distal ends (dendrites) or are located just after sensory receptors that are
separate cells. Once an appropriate stimulus activates a sensory receptor,
the sensory neuron forms an action potential in its axon and the action
potential is conveyed into the CNS through cranial or spinal nerves. Most
sensory neurons are unipolar in structure.
2. Motor or efferent neurons (ef- away from) convey action potentials away
from the CNS to effectors (muscles and glands) in the periphery (PNS) through
cranial or spinal nerves. Motor neurons are multipolar in structure.
3. Interneurons or association neurons are mainly located within the CNS
between sensory and motor neurons. Interneurons integrate (process)
incoming sensory information from sensory neurons and then elicit a motor
response by activating the appropriate motor neurons. Most interneurons are
multipolar in structure.
Neuroglia
Glial cells, or neuroglia or simply glia, are the other type of cell found in nervous
tissue. They are supporting cells, and many functions are directed at helping neurons
complete their function for communication. The name glia comes from the Greek word
that means “glue,” and was coined by the German pathologist Rudolph Virchow. There
are six types of glial cells. Four of them are found in the CNS and two are found in the
PNS.
Glial Cells of the Central Nervous System
1. Astrocyte - so named because it appears to be star-shaped under the
microscope. Astrocytes have many processes extending from their main cell body
(not axons or dendrites like neurons, just cell extensions). Those processes extend
to interact with neurons, blood vessels, or the connective tissue covering the CNS
that is called the pia mater. Generally, they are supporting cells for the neurons in
the central nervous system. Some ways in which they support neurons in the
central nervous system are by maintaining the concentration of chemicals in the
extracellular space, removing excess signaling molecules, reacting to tissue
damage, and contributing to the blood-brain barrier (BBB). The blood-brain barrier
is a physiological barrier that keeps many substances that circulate in the rest of
the body from getting into the central nervous system, restricting what can cross
from circulating blood into the CNS. Nutrient molecules, such as glucose or amino
acids, can pass through the BBB, but other molecules cannot.
2. Oligodendrocyte - sometimes called just “oligo” which is the glial cell type that
insulates axons in the CNS. The name means “cell of a few branches”. There are a
few processes that extend from the cell body. Each one reaches out and
surrounds an axon to insulate it in myelin. One oligodendrocyte will provide the
myelin for multiple axon segments, either for the same axon or for separate axons.
3. Microglia – are smaller than most of the other glial cells. Their function is related to
what macrophages do in the rest of the body. When macrophages encounter
diseased or damaged cells in the rest of the body, they ingest and digest those
cells or the pathogens that cause disease. Microglia are the cells in the CNS that
can do this in normal, healthy tissue, and they are therefore also referred to as
CNS-resident macrophages. They remove cellular debris formed during normal
development of the nervous system and phagocytize microbes and damaged
nervous tissue.
4. Ependymal cell - is a glial cell that filters blood to make cerebrospinal fluid (CSF),
the fluid that circulates through the CNS. Because of the privileged blood supply
inherent in the BBB, the extracellular space in nervous tissue does not easily
exchange components with the blood. Ependymal cells line each ventricle, one
of four central cavities that are remnants of the hollow center of the neural tube
formed during the embryonic development of the brain. The choroid plexus is a
specialized structure in the ventricles where ependymal cells meet blood vessels
and filter and absorb components of the blood to produce cerebrospinal fluid.
Because of this, ependymal cells can be considered a component of the BBB, or
a place where the BBB breaks down. These glial cells appear similar to epithelial
cells, making a single layer of cells with little intracellular space and tight
connections between adjacent cells. They also have cilia on their apical surface
to help move the CSF through the ventricular space.
Glial Cells of the Peripheral Nervous System
1. Satellite cells - are found in sensory and autonomic ganglia, where they
surround the cell bodies of neurons. This accounts for the name, based on their
appearance under the microscope. They provide support, performing similar
functions in the periphery as astrocytes do in the CNS—except, of course, for
establishing the BBB.
2. Schwann cell – are glial cells which insulate axons with myelin in the periphery.
Schwann cells are different than oligodendrocytes, in that a Schwann cell
wraps around a portion of only one axon segment and no others.
Oligodendrocytes have processes that reach out to multiple axon segments,
whereas the entire Schwann cell surrounds just one axon segment. The nucleus
and cytoplasm of the Schwann cell are on the edge of the myelin sheath.
Myelin Sheath – are multilayered lipids and proteins that covers the axons. The sheath
electrically insulates the axon of a neuron and increases the speed of nerve impulse
conduction.
Gray and White Matter
White matter is composed primarily of myelinated axons. The whitish color of
myelin gives white matter its name. The gray matter of the nervous system contains
neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. It
appears grayish, rather than white, because the Nissl bodies impart a gray color and
there is little or no myelin in these areas. Blood vessels are present in both white and
gray matter. In the spinal cord, the white matter surrounds an inner core of gray matter
that, depending on how imaginative you are, is shaped like a butterfly or the letter H in
transverse section; in the brain, a thin shell of gray matter covers the surface of the
largest portions of the brain, the cerebrum and cerebellum.
Synapse – the site of communication between two neurons or between a neuron and
an effector cell. The tips of some axon terminals swell into bulb-shaped structures
called synaptic end bulbs; others exhibit a string of swollen bumps called varicosities.
Both synaptic end bulbs and varicosities contain many tiny membrane-enclosed sacs
called synaptic vesicles that store a chemical called a neurotransmitter. A
neurotransmitter is a molecule released from a synaptic vesicle that excites or inhibits
another neuron, muscle fiber, or gland cell. Many neurons contain two or even three
types of neurotransmitters, each with different effects on the postsynaptic cell.
Cerebrospinal Fluid
Cerebrospinal fluid (CSF) is a clear, colorless liquid composed primarily of water
that protects the brain and spinal cord from chemical and physical injuries. It also carries
small amounts of oxygen, glucose, and other needed chemicals from the blood to
neurons and neuroglia. CSF continuously circulates through cavities in the brain and
spinal cord and around the brain and spinal cord in the subarachnoid space (the space
between the arachnoid mater and pia mater). CSF contains small amounts of glucose,
proteins, lactic acid, urea, cations (Na, K, Ca2, Mg2), and anions (Cl–and HCO3–); it also
contains some white blood cells. The four CSF-filled cavities within the brain are called
ventricles (little cavities). There is one lateral ventricle in each hemisphere of the
cerebrum. Anteriorly, the lateral ventricles are separated by a thin membrane, the
septum pellucidum. The third ventricle is a narrow slit-like cavity along the midline superior
to the hypothalamus and between the right and left halves of the
thalamus. The fourth ventricle lies between the brain stem and the cerebellum.
Protective Coverings of the Brain and Spinal Cord
The outer surface of the CNS is covered by a series of membranes composed of
connective tissue called the meninges, which protect the brain. The dura mater is a thick
fibrous layer and a strong protective sheath over the entire brain and spinal cord. It is
anchored to the inner surface of the cranium and vertebral cavity. The arachnoid mater
is a membrane of thin fibrous tissue that forms a loose sac around the CNS. Beneath the
arachnoid is a thin, filamentous mesh called the arachnoid trabeculae, which looks like
a spider web, giving this layer its name. Directly adjacent to the surface of the CNS is the
pia mater, a thin fibrous membrane that follows the convolutions of gyri and sulci in the
cerebral cortex and fits into other grooves and indentations.
Atlas of the Human Brain
The brain is a complex organ composed of gray parts and white matter, which
can be hard to distinguish. Starting from an embryologic perspective allows you to
understand more easily how the parts relate to each other. The embryonic nervous
system begins as a very simple structure—essentially just a straight line, which then gets
increasingly complex.
The Neural Tube
As the embryo develops, a portion of the ectoderm differentiates into a
specialized region of neuroectoderm, which is the precursor for the tissue of the nervous
system. Molecular signals induce cells in this region to differentiate into the
neuroepithelium, forming a neural plate. The cells then begin to change shape, causing
the tissue to buckle and fold inward. A neural groove forms, visible as a line along the
dorsal surface of the embryo. The ridge-like edge on either side of the neural groove is
referred as the neural fold. As the neural folds come together and converge, the
underlying structure forms into a tube just beneath the ectoderm called the neural tube.
Cells from the neural folds then separate from the ectoderm to form a cluster of cells
referred to as the neural crest, which runs lateral to the neural tube. The neural crest
migrates away from the nascent, or embryonic, central nervous system (CNS) that will
form along the neural groove and develops into several parts of the peripheral nervous
system (PNS), including the enteric nervous tissue.
Primary Vesicles
As the anterior end of the neural tube starts to develop into the brain, it undergoes
a couple of enlargements; the result is the production of sac-like vesicles. Three vesicles
form at the first stage, which are called primary vesicles. The prosencephalon (pros- = “in
front”) is the forward-most vesicle, and the term can be loosely translated to mean
forebrain. The mesencephalon (mes- = “middle”) is the next vesicle, which can be called
the midbrain. The third vesicle at this stage is the rhombencephalon. One way of thinking
about how the brain is arranged is to use these three regions—forebrain, midbrain, and
hindbrain—which are based on the primary vesicle stage of development.
Secondary Vesicles
The brain continues to develop, and the vesicles differentiate further. The three
primary vesicles become five secondary vesicles. The prosencephalon enlarges into two
new vesicles called the telencephalon and the diencephalon. The telencephalon will
become the cerebrum. The diencephalon gives rise to several adult structures; two that
will be important are the thalamus and the hypothalamus. In the embryonic
diencephalon, a structure known as the eye cup develops, which will eventually become
the retina. This is a rare example of nervous tissue developing as part of the CNS structures
in the embryo but becoming a peripheral structure in the fully formed nervous system.
The mesencephalon does not differentiate into any finer divisions. The midbrain is an
established region of the brain at the primary vesicle stage of development and remains
that way. The rest of the brain develops around it and constitutes a large percentage of
the mass of the brain. Dividing the brain into forebrain, midbrain, and hindbrain is useful
in considering its developmental pattern, but the midbrain is a small proportion of the
entire brain, relatively speaking. The rhombencephalon develops into the
metencephalon and myelencephalon. The metencephalon corresponds to the adult
structure known as the pons and gives rise to the cerebellum. The cerebellum (from the
Latin meaning “little brain”) accounts for about 10 percent of the mass of the brain and
is an important structure. The most significant connection between the cerebellum and
the rest of the brain is at the pons because the pons and cerebellum develop out of the
same vesicle. The myelencephalon corresponds to the adult structure known as the
medulla oblongata. The structures that come from the mesencephalon and
rhombencephalon, except for the cerebellum, are collectively considered the brain
stem, which specifically includes the midbrain, pons, and medulla.
Major Regions of the Human Adult Brain
1. Cerebrum - The iconic gray mantle of the human brain, which appears to make
up most of the mass of the brain, is the cerebrum. The wrinkled portion is the
cerebral cortex, and the rest of the structure is beneath that outer covering.
There is a large separation between the two sides of the cerebrum called the
longitudinal fissure. It separates the cerebrum into two distinct halves, a right and
left cerebral hemisphere. Deep within the cerebrum, the white matter of the
corpus callosum provides the major pathway for communication between the
two hemispheres of the cerebral cortex. In mammals, the cerebrum comprises
the outer gray matter that is the cortex (from the Latin word meaning “bark of a
tree”) and several deep nuclei that belong to three important functional groups.
The basal nuclei are responsible for cognitive processing, the most important
function being that associated with planning movements. The basal forebrain
contains nuclei that are important in learning and memory. The limbic cortex is
the region of the cerebral cortex that is part of the limbic system, a collection of
structures involved in emotion, memory, and behavior.
1a. Cerebral Cortex
The cerebrum is covered by a continuous layer of gray matter that wraps
around either side of the forebrain—the cerebral cortex. The folding of the cortex
maximizes the amount of gray matter in the cranial cavity. The surface of the
brain can be mapped on the basis of the locations of large gyri and sulci.
Using these landmarks, the cortex can be separated into four major regions, or
lobes. The lateral sulcus that separates the temporal lobe from the other regions
is one such landmark. Superior to the lateral sulcus are the parietal lobe and
frontal lobe, which are separated from each other by the central sulcus. The
posterior region of the cortex is the occipital lobe, which has no obvious
anatomical border between it and the parietal or temporal lobes on the lateral
surface of the brain. From the medial surface, an obvious landmark separating
the parietal and occipital lobes is called the parieto-occipital sulcus.
2.
Diencephalon - The rest of the brain, the spinal cord, and the PNS all send
information to the cerebrum through the diencephalon. Output from the cerebrum
passes through the diencephalon. The single exception is the system associated with
olfaction, or the sense of smell, which connects directly with the cerebrum. The
diencephalon is deep beneath the cerebrum and constitutes the walls of the third
ventricle. The diencephalon can be described as any region of the brain with
“thalamus” in its name. The two major regions of the diencephalon are the thalamus
itself and the hypothalamus. There are other structures, such as the epithalamus, which
contains the pineal gland, or the subthalamus, which includes the subthalamic nucleus
that is part of the basal nuclei.
2a. Thalamus
The thalamus is a collection of nuclei that relay information between the
cerebral cortex and the periphery, spinal cord, or brain stem. All sensory
information, except for the sense of smell, passes through the thalamus before
processing by the cortex. Axons from the peripheral sensory organs, or
intermediate nuclei, synapse in the thalamus, and thalamic neurons project
directly to the cerebrum. It is a requisite synapse in any sensory pathway, except
for olfaction. The thalamus does not just pass the information on, it also processes
that information.
2b. Hypothalamus
The hypothalamus is a collection of nuclei that are largely involved in
regulating homeostasis. The hypothalamus is the executive region in charge of
the autonomic nervous system and the endocrine system through its regulation
of the anterior pituitary gland. Other parts of the hypothalamus are involved in
memory and emotion as part of the limbic system.
3.
Brainstem - The midbrain and hindbrain (composed of the pons and the
medulla) are collectively referred to as the brain stem. The structure emerges from the
ventral surface of the forebrain as a tapering cone that connects the brain to the spinal
cord. Attached to the brain stem, but considered a separate region of the adult brain,
is the cerebellum. The midbrain coordinates sensory representations of the visual,
auditory, and somatosensory perceptual spaces. The pons is the main connection with
the cerebellum. The pons and the medulla regulate several crucial functions, including
the cardiovascular and respiratory systems and rates.
3a. Midbrain
The midbrain is a small region between the thalamus and pons. It is
separated into the tectum and tegmentum. The tectum is composed of four
bumps known as the colliculi (singular = colliculus), which means “little hill” in
Latin. The inferior colliculus is the inferior pair of these enlargements and is part of
the auditory brain stem pathway. Neurons of the inferior colliculus project to the
thalamus, which then sends auditory information to the cerebrum for the
conscious perception of sound. The superior colliculus is the superior pair and
combines sensory information about visual space, auditory space, and
somatosensory space. Activity in the superior colliculus is related to orienting the
eyes to a sound or touch stimulus. The tegmentum is continuous with the gray
matter of the rest of the brain stem. Throughout the midbrain, pons, and medulla,
the tegmentum contains the nuclei that receive and send information through
the cranial nerves, as well as regions that regulate important functions such as
those of the cardiovascular and respiratory systems.
3b. Pons
The pons is the main connection between the cerebellum and the brain
stem. The bridge-like white matter is only the anterior surface of the pons; the
gray matter beneath that is a continuation of the tegmentum from the midbrain.
Gray matter in the tegmentum region of the pons contains neurons receiving
descending input from the forebrain that is sent to the cerebellum.
3c. Medulla
The medulla is the region known as the myelencephalon in the embryonic
brain. The initial portion of the name, “myel,” refers to the significant white matter
found in this region—especially on its exterior, which is continuous with the white
matter of the spinal cord. The tegmentum of the midbrain and pons continues
into the medulla because this gray matter is for processing cranial nerve
information. A diffuse region of gray matter throughout the brain stem, known as
the reticular formation, is related to sleep and wakefulness, such as general brain
activity and attention.
4.
Cerebellum - The cerebellum, as the name suggests, is the “little brain.” It is
covered in gyri and sulci like the cerebrum and looks like a miniature version of that part
of the brain. The cerebellum is largely responsible for comparing information from the
cerebrum with sensory feedback from the periphery through the spinal cord. It
accounts for approximately 10 percent of the mass of the brain.
The Spinal Cord
The spinal cord maintains the tube structure and is only specialized into certain
regions. As the spinal cord continues to develop in the newborn, anatomical
features mark its surface. the posterior regions are responsible for sensory functions
and the anterior regions are associated with motor functions. This comes from the
initial development of the spinal cord, which is divided into the basal plate and the
alar plate. The basal plate is closest to the ventral midline of the neural tube, which
will become the anterior face of the spinal cord and gives rise to motor neurons. The
alar plate is on the dorsal side of the neural tube and gives rise to neurons that will
receive sensory input from the periphery.
Gray Horns
The gray matter is subdivided into regions that are referred to as horns. The
posterior horn is responsible for sensory processing. The anterior horn sends out motor
signals to the skeletal muscles. The lateral horn, which is only found in the thoracic,
upper lumbar, and sacral regions, is the central component of the sympathetic
division of the autonomic nervous system.
White Columns
The white matter of the spinal cord is separated into columns. Ascending
tracts of nervous system fibers in these columns carry sensory information up to the
brain, whereas descending tracts carry motor commands from the brain. Looking at
the spinal cord longitudinally, the columns extend along its length as continuous
bands of white matter. Between the two posterior horns of gray matter are the
posterior columns. Between the two anterior horns and bounded by the axons of
motor neurons emerging from that gray matter area, are the anterior columns. The
white matter on either side of the spinal cord, between the posterior horn and the
axons of the anterior horn neurons, are the lateral columns. The posterior columns
are composed of axons of ascending tracts. The anterior and lateral
columns are composed of many different groups of axons of both ascending and
descending tracts—the latter carrying motor commands down from the brain to the
spinal cord to control output to the periphery.
The Eye and the Ear
Vision
Vision is the special sense of sight that is based on the transduction of light stimuli
received through the eyes. The eyes are located within either orbit in the skull. The
bony orbits surround the eyeballs, protecting them and anchoring the soft tissues of
the eye. The eyelids, with lashes at their leading edges, help to protect the eye from
abrasions by blocking particles that may land on the surface of the eye. The inner
surface of each lid is a thin membrane known as the palpebral conjunctiva. The
conjunctiva extends over the white areas of the eye (the sclera), connecting the
eyelids to the eyeball. Tears are produced by the lacrimal gland, located beneath
the lateral edges of the nose. Tears produced by this gland flow through the
lacrimal duct to the medial corner of the eye, where the tears flow over the
conjunctiva, washing away foreign particles.
Eye Movement
Movement of the eye within the orbit is accomplished by the contraction of six
extraocular muscles that originate from the bones of the orbit and insert into the
surface of the eyeball. Four of the muscles are arranged at the cardinal points around
the eye and are named for those locations. They are the superior rectus, medial
rectus, inferior rectus, and lateral rectus. When each of these muscles contract, the
eye to moves toward the contracting muscle. The superior oblique originates at the
posterior orbit, near the origin of the four rectus muscles. However, the tendon of the
oblique muscles threads through a pulley-like piece of cartilage known as the
trochlea. The tendon inserts obliquely into the superior surface of the eye. The angle
of the tendon through the trochlea means that contraction of the superior oblique
rotates the eye medially. The inferior oblique muscle originates from the floor of the
orbit and inserts into the inferolateral surface of the eye. When it contracts, it laterally
rotates the eye, in opposition to the superior oblique. Rotation of the eye by the two
oblique muscles is necessary because the eye is not perfectly aligned on the sagittal
plane. A seventh muscle in the orbit is the levator palpebrae superioris, which is
responsible for elevating and retracting the upper eyelid, a movement that usually
occurs in concert with elevation of the eye by the superior rectus.
Structure of the Eye
The eye itself is a hollow sphere composed of three layers of tissue. The outermost
layer is the fibrous tunic, which includes the white sclera and clear cornea. The sclera
accounts for five sixths of the surface of the eye, most of which is not visible, though
humans are unique compared with many other species in having so much of the
“white of the eye” visible. The transparent cornea covers the anterior tip of the eye
and allows light to enter the eye. The middle layer of the eye is the vascular tunic,
which is mostly composed of the choroid, ciliary body, and iris. The choroid is a layer
of highly vascularized connective tissue that provides a blood supply to the eyeball.
The choroid is posterior to the ciliary body, a muscular structure that is attached to
the lens by suspensory ligaments, or zonule fibers. These two structures bend the lens,
allowing it to focus light on the back of the eye. Overlaying the ciliary body, and
visible in the anterior eye, is the iris—the colored part of the eye. The iris is a smooth
muscle that opens or closes the pupil, which is the hole at the center of the eye that
allows light to enter. The iris constricts the pupil in response to bright light and dilates
the pupil in response to dim light. The innermost layer of the eye is the neural tunic, or
retina, which contains the nervous tissue responsible for photoreception. The eye is
also divided into two cavities: the anterior cavity and the posterior cavity. The anterior
cavity is the space between the cornea and lens, including the iris and ciliary body.
It is filled with a watery fluid called the aqueous humor. The posterior cavity is the
space behind the lens that extends to the posterior side of the interior eyeball, where
the retina is located. The posterior cavity is filled with a more viscous fluid called the
vitreous humor. The retina is composed of several layers and contains specialized cells
for the initial processing of visual stimuli. The photoreceptors (rods and cones) change
their membrane potential when stimulated by light energy. The change in membrane
potential alters the amount of neurotransmitter that the photoreceptor cells release
onto bipolar cells in the outer synaptic layer. It is the bipolar cell in the retina that
connects a photoreceptor to a retinal ganglion cell (RGC) in the inner synaptic layer.
There, amacrine cells additionally contribute to retinal processing before an action
potential is produced by the RGC. The axons of RGCs, which lie at the innermost layer
of the retina, collect at the optic disc and leave the eye as the optic nerve. Because
these axons pass through the retina, there are no photoreceptors at the very back of
the eye, where the optic nerve begins. This creates a “blind spot” in the retina, and a
corresponding blind spot in our visual field.
Seeing
Light falling on the retina causes chemical changes to pigment molecules in the
photoreceptors, ultimately leading to a change in the activity of the RGCs.
Photoreceptor cells have two parts, the inner segment and the outer segment. The
inner segment contains the nucleus and other common organelles of a cell, whereas
the outer segment is a specialized region in which photoreception takes place. There
are two types of photoreceptors—rods and cones—which differ in the shape of their
outer segment. The rod-shaped outer segments of the rod photoreceptor contain a
stack of membrane-bound discs that contain the photosensitive pigment rhodopsin.
The cone-shaped outer segments of the cone photoreceptors contain their
photosensitive pigments in infoldings of the cell membrane. There are three cone
photopigments, called opsins, which are each sensitive to a particular wavelength of
light. The wavelength of visible light determines its color. The pigments in human eyes
are specialized in perceiving three different primary colors: red, green, and blue.
Rhodopsin, the photopigment in rods, is most sensitive to light at a wavelength of
498 nm. The three-color opsins have peak sensitivities of 564 nm, 534 nm, and 420 nm
corresponding roughly to the primary colors of red, green, and blue. The absorbance
of rhodopsin in the rods is much more sensitive than in the cone opsins; specifically,
rods are sensitive to vision in low light conditions, and cones are sensitive to brighter
conditions. The three types of cone opsins, being sensitive to different wavelengths of
light, provide us with color vision. By comparing the activity of the three different
cones, the brain can extract color information from visual stimuli.
Audition
Hearing, or audition, is the transduction of sound waves into a neural signal that is
made possible by the structures of the ear. The large, fleshy structure on the lateral
aspect of the head is known as the auricle. Some sources will also refer to this structure
as the pinna, though that term is more appropriate for a structure that can be moved,
such as the external ear of a cat. The C-shaped curves of the auricle direct sound
waves toward the auditory canal. The canal enters the skull through the external
auditory meatus of the temporal bone. At the end of the auditory canal is the
tympanic membrane, or ear drum, which vibrates after it is struck by sound waves.
The auricle, ear canal, and tympanic membrane are often referred to as the external
ear. The middle ear consists of a space spanned by three small bones called the
ossicles. The three ossicles are the malleus, incus, and stapes, which are Latin names
that roughly translate to hammer, anvil, and stirrup. The malleus is attached to the
tympanic membrane and articulates with the incus. The incus, in turn, articulates with
the stapes. The stapes is then attached to the inner ear, where the sound waves will
be transduced into a neural signal. The middle ear is connected to the pharynx
through the Eustachian tube, which helps equilibrate air pressure across the tympanic
membrane.
Structure of the Ear
The inner ear is often described as a bony labyrinth, as it is composed of a series
of canals embedded within the temporal bone. It has two separate regions, the
cochlea and the vestibule, which are responsible for hearing and balance,
respectively. The neural signals from these two regions are relayed to the brain stem
through separate fiber bundles. However, these two distinct bundles travel together
from the inner ear to the brain stem as the vestibulocochlear nerve. Sound is
transduced into neural signals within the cochlear region of the inner ear, which
contains the sensory neurons of the spiral ganglia. These ganglia are located within
the spiral-shaped cochlea of the inner ear. The cochlea is attached to the stapes
through the oval window. The oval window is located at the beginning of a fluid-filled
tube within the cochlea called the scala vestibuli. The scala vestibuli extends from the
oval window, travelling above the cochlear duct, which is the central cavity of the
cochlea that contains the sound-transducing neurons. At the uppermost tip of the
cochlea, the scala vestibuli curves over the top of the cochlear duct. The fluid-filled
tube, now called the scala tympani, returns to the base of the cochlea, this time
travelling under the cochlear duct. The scala tympani ends at the round window,
which is covered by a membrane that contains the fluid within the scala. As vibrations
of the ossicles travel through the oval window, the fluid of the scala vestibuli and scala
tympani moves in a wave-like motion. The frequency of the fluid waves match the
frequencies of the sound waves. The membrane covering the round window will
bulge out or pucker in with the movement of the fluid within the scala tympani.
Hearing
A sound wave causes the tympanic membrane to vibrate. This vibration is
amplified as it moves across the malleus, incus, and stapes. The amplified vibration is
picked up by the oval window causing pressure waves in the fluid of the scala
vestibuli and scala tympani. The complexity of the pressure waves is determined by
the changes in amplitude and frequency of the sound waves entering the ear.
The cochlear duct contains several organs of Corti, which tranduce the wave
motion of the two scala into neural signals. The organs of Corti lie on top of the basilar
membrane, which is the side of the cochlear duct located between the organs of
Corti and the scala tympani. As the fluid waves move through the scala vestibuli and
scala tympani, the basilar membrane moves at a specific spot, depending on the
frequency of the waves. Higher frequency waves move the region of the basilar
membrane that is close to the base of the cochlea. Lower frequency waves move
the region of the basilar membrane that is near the tip of the cochlea.
The organs of Corti contain hair cells, which are named for the hair-like stereocilia
extending from the cell’s apical surfaces. The stereocilia are an array of microvilli-like
structures arranged from tallest to shortest. Protein fibers tether adjacent hairs
together within each array, such that the array will bend in response to movements
of the basilar membrane. The stereocilia extend up from the hair cells to the overlying
tectorial membrane, which is attached medially to the organ of Corti. When the
pressure waves from the scala move the basilar membrane, the tectorial membrane
slides across the stereocilia.
UNIVERSITY OF CALOOCAN CITY
Biglang Awa St., Corner Catleya St., EDSA, Caloocan City
COLLEGE OF EDUCATION
Anatomy and Physiology
SUBJECT CODE:
TOPIC OR LESSON:
WEEK:
SUB-TOPIC/S:
MBS 313
Muscular System
7
1. The Anterior Skeletal Muscle
2. The Posterior Skeletal Muscle
3. The Histology of Muscle Tissue
OVERVIEW OF THE TOPIC
Although bones provide leverage and form the framework of the body,
they cannot move body parts by themselves. Motion results from the alternating
contraction and relaxation of muscles, which make up 40–50% of total adult body
weight (depending on the percentage of body fat, gender, and exercise
regimen). Your muscular strength reflects the primary function of muscle—the
transformation of chemical energy into mechanical energy to generate force,
perform work, and produce movement. In addition, muscle tissues stabilize body
position, regulate organ volume, generate heat, and propel fluids and food
matter through various body systems.
In this module, you will learn that muscles are the tissues in animals that
allows for active movement of the body or materials within the body. There are
three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle.
Most of the body’s skeletal muscle produces movement by acting on the
skeleton. Cardiac muscle is found in the wall of the heart and pumps blood
through the circulatory system. Smooth muscle is found in the skin, where it is
associated with hair follicles; it also is found in the walls of internal organs, blood
vessels, and internal passageways, where it assists in moving materials. Skeletal
muscles contain connective tissue, blood vessels, and nerves. Skeletal muscle
fibers are organized into groups called fascicles. Blood vessels and nerves enter
the connective tissue and branch in the cell. Muscles attach to bones directly or
through tendons or aponeuroses. Skeletal muscles maintain posture, stabilize
bones and joints, control internal movement, and generate heat.
a.
Correctly identify the muscles in the anterior and posterior part of the
human body;
b.
Explain the process of muscle contraction and relaxation; and
c.
Write an analysis paper that tackles and examines Chiropractic care for
Multiple Sclerosis.
At the end of the lesson, students should be able to:
a.
b.
c.
identify the skeletal muscles found in the anterior part;
enumerate the different muscles found in the posterior part; and
discuss the histology of the muscle tissue.
Naming of Skeletal Muscles
Anatomists name the skeletal muscles according to a number of criteria, each of
which describes the muscle in some way. These include naming the muscle after its
shape, its size compared to other muscles in the area, its location in the body or the
location of its attachments to the skeleton, how many origins it has, or its action.
The skeletal muscle’s anatomical location or its relationship to a particular bone
often determines its name. For example, the frontalis muscle is located on top of the
frontal bone of the skull. Similarly, the shapes of some muscles are very distinctive and the
names, such as orbicularis, reflect the shape. For the buttocks, the size of the muscles
influences the names: gluteus maximus (largest), gluteus medius (medium), and the
gluteus minimus (smallest). Names were given to indicate length— brevis (short), longus
(long)—and to identify position relative to the midline: lateralis (to the outside/ away from
the midline), and medialis (toward the midline). The direction of the muscle fibers and
fascicles are used to describe muscles relative to the midline, such as the rectus (straight)
abdominis, or the oblique (at an angle) muscles of the abdomen.
Name
Description/Meaning
Example
DIRECTION: Orientation of muscle fascicles relative to the body’s midline
Rectus
Parallel to midline
Rectus abdominis
Transverse
Perpendicular to midline
Transversus abdominis
Oblique
Diagonal to midline
External oblique
SIZE: Relative size of the muscle
Maximus
Largest
Gluteus maximus
Minimus
Smallest
Gluteus minimus
Longus
Long
Adductor longus
Brevis
Short
Adductor brevis
Latissimus
Widest
Latissimus dorsi
Longissimus Longest
Longissimus capitis
Magnus
Large
Adductor magnus
Major
Larger
Pectoralis major
Minor
Smaller
Pectoralis minor
Vastus
Huge
Vastus lateralis
SHAPE: Relative shape of the muscle
Deltoid
Triangular
Deltoid
Trapezius
Trapezoid
Trapezius
Serratus
Saw-toothed
Serratus anterior
Rhomboid
Diamond-shaped
Rhomboid major
Orbicularis
Circular
Orbicularis oculi
Pectinate
Comblike
Pectineus
Piriformis
Pear-shaped
Piriformis
Platys
Flat
Platysma
Quadratus
Square, four-sided
Quadratus femoris
Gracilis
Slender
ACTION: Principal action of the muscle
Flexor
Decreases joint angle
Extensor
Increases joint angle
Abductor
Moves bone away from midline
Adductor
Moves bone closer to midline
Levator
Raises or elevates body part
Depressor
Lowers or depresses body part
Supinator
Turns palm anteriorly
Pronator
Turns palm posteriorly
Sphincter
Decreases size of an opening
Tensor
Makes body part rigid
Rotator
Rotates bone around longitudinal axis
NUMBER OF ORIGINS: Number of tendons of origin
Biceps
Two origins
Triceps
Three origins
Quadriceps Four origins
Gracilis
Flexor carpi radialis
Extensor carpi ulnaris
Abductor pollicis longus
Adductor longus
Levator scapulae
Depressor labii inferioris
Supinator
Pronator teres
External anal sphincter
Tensor fasciae latae
Rotatore
Biceps brachii
Triceps brachii
Quadriceps femoris
Anterior Skeletal Muscle
Muscles that Create Facial Expression
Many of the muscles of facial expression insert into the skin surrounding the eyelids,
nose and mouth, producing facial expressions by moving the skin rather than bones.
A.
Orbicularis oris - is a circular muscle that moves the lips.
B.
Orbicularis oculi - is a circular muscle that closes the eye.
C.
Occipitofrontalis - muscle moves up the scalp and eyebrows. The muscle has a
frontal belly and an occipital (near the occipital bone on the posterior part of the skull)
belly. In other words, there is a muscle on the forehead ( frontalis) and one on the back
of the head ( occipitalis), but there is no muscle across the top of the head. Instead, the
two bellies are connected by a broad tendon called the epicranial aponeurosis, or galea
aponeurosis (galea = “apple
D.
Buccinator muscle - compresses the cheek. This muscle allows you to whistle, blow,
and suck; and it contributes to the action of chewing.
E.
Corrugator supercilia - which is the prime mover of the eyebrows.
Other Muscles that contribute to Facial Expression
Muscle
Brow
Occipitofrontalis
– frontal belly
Movement
Occipitofrontalis
– occipital belly
Unfurrowing
brow
Target
Origin
Furrowing of brow Skin of the Epicranial
scalp
aponeurosis
Insertion
Underneath he
skin of the
forehead
of Skin of the Occipital
Epicranial
scalp
bone; mastoid aponeurosis
process
(temporal
bone)
Corrugator
supercilii
Lowering
eyebrows
Frontal bone
Skin
underneath
eyebrows
Nose
Nasalis
Flaring of nostrils
Nasal
cartilage
Maxilla
Nasal bone
Mouth
Levator
superioris
labii Raising the upper Upper lip
lip
Maxilla
Depressor
inferioris
labii Lowering
lower lip
Mandible
Underneath
skin at corners
of the mouth
Underneath
the skin of the
lower lip
Underneath
skin at corners
of the mouth
Depressor
angulus oris
Zygomaticus
major
of Skin
underneath
the
eyebrows
the Lower lip
Opening of the Lower jaw
Mandible
mouth and sliding
the lower jaw left
and right
Smiling
Corners
of Zygomatic
the mouth
bone
Orbicularis oris
Shaping of lips (as Lips
during speech)
Buccinator
Lateral
movement of the
cheeks (sucking
using
straw;
compressing air
when blowing)
Pursing the lips
when
straightening
them laterally
Protrusion of the
lower lip
Risorius
Mentalis
Cheeks
Tissue
surrounding
lips
Maxilla,
mandible,
sphenoid
bone
Underneath
skin at the
corners of the
mouth (dimple
area)
Underneath
skin at corners
of mouth
Orbicularis oris
Corners
of Fascia
of Underneath
the mouth
parotid
skin at corners
salivary gland of the mouth
Lower
lip Mandible
and skin of
chin
Underneath
skin of chin
Muscles that Move the Eyes
The movement of the eyeball is under the control of the extrinsic eye muscles,
which originate outside the eye and insert onto the outer surface of the white of the
eye. These muscles are located inside the eye socket and cannot be seen on any part
of the visible eyeball.
Muscle
Superior
rectus
Target
Eyeballs
Lateral
rectus
Movement
Moves the eyes up
and forward;
moves the eye
from 1o’clock to
3o’clock
Moves the eyes
down and toward
the nose; rotates
the eyes from
3o’clock to
6o’clock
Moves eyes away
from the nose
Medial
rectus
Moves eyes toward
the nose
Eyeballs
Inferior
Oblique
Moves the eyes up
and away from the
nose; rotates the
eyeball from
9o’clock to
12o’clock
Moves the eye
down and away
from the nose;
rotates eyeball
from 6o’clock to
9o’clock
Opens eyes
Eyeballs
Closes eyelids
Inferior
rectus
Superior
oblique
Levator
palpabrae
superioris
Orbicularis
oculi
Origin
Common
tendinous ring
(ring attaches to
the optic
foramen)
Common
tendinous ring
(ring attaches to
the optic
foramen)
Insertion
Superior surface of
the eyeball
Common
tendinous ring
(ring attaches to
the optic
foramen)
Common
tendinous ring
(ring attaches to
the optic
foramen)
Floor of the orbit
(maxilla)
Lateral surface of
the eyeball
Eyeballs
Sphenoid bone
Surface of the
eyeball between
superior rectus and
lateral rectus
Upper
eyelid
Roof of orbit
Skin of upper
(sphenoid bone) eyelids
Eyelid
skin
Medial bones
composing the
orbit
Eyeballs
Eyeballs
Inferior surface of
the eyeball
Media surface of the
eyeball
Surface of the
eyeball between
the inferior rectus
and lateral rectus
Circumference of
orbit
Muscles that Move the Lower Jaw
Chewing is called mastication. Muscles involved in chewing must be able to exert
enough pressure to bite through and then chew food before it is swallowed. The masseter
muscle is the main muscle used for chewing because it elevates the mandible (lower
jaw) to close the mouth, and it is assisted by the temporalis muscle, which retracts the
mandible. You can feel the temporalis move by putting your fingers
you chew.
Muscle
Movement
Target
Origin
Masseter
Closes mouth; aids chewing
Mandible Maxilla
arch;
zygomatic
arch (for
masseter)
Temporalis Closes mouth; pulls lower
Mandible Temporal
jaw in under upper jaw
bone
Lateral
Opens mouth; pushes lower
Mandible Pterygoid
pterygoid jaw out under upper jaw;
process of
moves lower jaw side to side
sphenoid
bone
Medial
Closes mouth; pushes
Mandible Sphenoid
pterygoid lower jaw out under upper
bone;
jaw; moves lower jaw side to
maxilla
side
to your temple as
Insertion
Mandible
Mandible
Mandible
Mandible;
Temporomandibular
joint
Muscles that Move the Tongue
Although the tongue is obviously important for tasting food, it is also necessary for
mastication, deglutition (swallowing), and speech. Because it is so moveable, the
tongue facilitates complex speech patterns and sounds.
Muscle
Movement
Target
Origin
Insertion
Genioglossus
Moves the tongue Tongue
Mandible
Tongue
down; sticks
undersurface;
tongue out of the
hyoid bone
mouth
Styloglossus
Moves tongue up; Tongue
Temporal
Tongue
retracts tongue
bone
undersurface
back into mouth
(styloid
and sides
process)
Hyoglossus
Flatten tongue
Tongue
Hyoid
Sides of the
bone
tongue
Palatoglossus
Bulges tongue
Tongue
Soft
Side on
palate
tongue
Swallowing and Speaking
Digastric
Raises the hyoid
Hyoid
Mandible; Hyoid bone
bone in a way
bone;
temporal
that also raises the larynx
bone
larynx, allowing
the epiglottis to
cover the glottis
during deglutition;
also assist in
opening the
Stylohyoid
Mylohyoid
Geniohyoid
Omohyoid
Sternohyoid
Thyrohyoid
Sternothyroid
mouth by
depressing the
mandible
Raises and retracts
the hyoid bone in
a way that
elongates the oral
cavity during
deglutition
Raises hyoid bone
in a way that
presses the
tongue against
the roof of the
mouth, pushing
food back into the
pharynx during
deglutition
Raises and moves
hyoid bone
forward, widening
pharynx during
deglutition
Retracts the hyoid
bone and moves
it down during
later phases of
deglutition
Depresses the
hyoid bone during
swallowing and
speaking
Shrinks distance
between thyroid
cartilage and
hyoid bone,
allowing
production of
high-pitch
vocalizations
Depresses larynx,
thyroid cartilage,
and hyoid bone to
create different
vocals tones
Hyoid
bone
Temporal
bone
(styloid
process)
Hyoid bone
Hyoid
bone
Mandible
Hyoid bone;
median raphe
Hyoid
bone
Mandible
Hyoid bone
Hyoid
bone
Scapula
Hyoid bone
Hyoid
bone
Clavicle
Hyoid bone
Hyoid
bone;
thyroid
cartilage
Thyroid
cartilage
Hyoid bone
Larynx;
thyroid
cartilage;
hyoid
bone
Sternum
Thyroid
cartilage
Sternocleidomastoid;
Semispinalis capitis
Rotates and tilts
head to the side,
tilts head forward
Skull;
cervical
vertebrae
Splenius capitis;
longissimus capitis
Rotates and tilts
head to the side;
tilts head
backwards
Skull;
cervical
vertebrae
Sternum;
clavicle
Temporal
bone (mastoid
process);
occipital bone
Muscles of the Abdomen
There are four pairs of abdominal muscles that cover the anterior and lateral
abdominal region and meet at the anterior midline. These muscles of the anterolateral
abdominal wall can be divided into four groups: the external obliques, the internal
obliques, the transversus abdominis, and the rectus abdominis.
Muscle
Movement
Target
Origin
Insertion
External
Twisting at waist; also
Vertebral
Ribs 5–12; Ribs 7–10; linea
obliques;
bending to the
column
ilium
alba; ilium
internal
side
obliques
Transversus
Squeezing abdomen
Abdominal Ilium; ribs
Sternum; linea
abdominus
during forceful
cavity
5–10
alba; pubis
exhalations, defecation,
urination, and
childbirth
Rectus
Sitting up
Vertebral
Pubis
Sternum; ribs 5
abdominis
column
and 7
Quadratus
Bending to the side
Vertebral
Ilium; ribs
Rib 12; Vertebrae
lumborum
column
5–10
L1–L4
Muscles of the Thorax
The muscles of the chest serve to facilitate breathing by changing the size of the
thoracic cavity. When you inhale, your chest rises because the cavity expands.
Alternately, when you exhale, your chest falls because the thoracic cavity decreases in
size.
Muscle
Movement
Target
Origin
Insertion
Diaphragm Inhalation;
Thoracic
Sternum;
Central
Exhalation (compression;
Cavity
ribs
tendon
expansion)
6–12;
lumbar
vertebrae
External
Inhalation; exhalation
Ribs
Rib superior Rib inferior
intercostals (elevation; expands thoracic
to
to
cavity)
each
each
intercostal
intercostal
muscle
muscle
Internal
Forced exhalation
Ribs
Rib inferior
Rib superior
intercostals
to
to
each
each
intercostal
intercostal
muscle
muscle
Defecating, urination, and even childbirth involve cooperation between the
diaphragm and abdominal muscles (this cooperation is referred to as the “Valsalva
maneuver”). You hold your breath by a steady contraction of the diaphragm; this
stabilizes the volume and pressure of the peritoneal cavity. When the abdominal muscles
contract, the pressure cannot push the diaphragm up, so it increases pressure on the
intestinal tract (defecation), urinary tract (urination), or reproductive tract (childbirth).
Muscles of the Pelvic Floor and Perineum
The pelvic floor is a muscular sheet that defines the inferior portion of the pelvic
cavity. The pelvic diaphragm, spanning anteriorly to posteriorly from the pubis to the
coccyx, comprises the levator ani and the ischiococcygeus. Its openings include the anal
canal and urethra, and the vagina in women. The large levator ani consists of two skeletal
muscles, the pubococcygeus and the iliococcygeus. The levator ani is considered the
most important muscle of the pelvic floor because it supports the pelvic viscera. It resists
the pressure produced by contraction of the abdominal muscles so that the pressure is
applied to the colon to aid in defecation and to the uterus to aid in childbirth (assisted
by the ischiococcygeus, which pulls the coccyx anteriorly). This muscle alsocreates
skeletal muscle sphincters at the urethra and anus.
The perineum is the diamond-shaped space between the pubic symphysis
(anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just
inferior to the pelvic diaphragm (levator ani and coccygeus). Divided transversely
into triangles, the anterior is the urogenital triangle, which includes the external genitals.
The posterior is the anal triangle,which contains the anus. The perineum is also divided
into superficial and deep layers with some of themuscles common to men and women.
Women also have the compressor urethrae and the sphincter urethrovaginalis, which
function to close the vagina. In men, there is the deep transverse perineal muscle that
plays a role in ejaculation.
Muscles of the Perineum Common to Men and Women
Muscle
Movement
Target
Origin
Levator ani
Defecation,
Abdominal Pubis; ischium
pubococcygeus;
urination,
cavity
levator ani
childbirth,
iliococcygeus
coughing
Superficial Muscles
Superficial
No movement.
Perineal
Ischium
transverse
Supports
body
perineal
perineal body
Insertion
Urethra; anal
canal;
perineal body,
coccyx
Perineal body
Bulbospongiosus
Ischiocavernosus
Deep Muscle
External urethral
sphincter
maintaining
anus at center
of perineum
Involuntary
response that
compresses
urethra when
excreting urine
in both sexes or
while
ejaculating in
males; also aids
in erection of
penis in males
Compresses
veins to
maintain
erection of
penis in males;
erection of
clitoris in
females
Voluntarily
compresses
urethra during
urination
Closes anus
Urethra
Perineal body
Perineal
Membrane;
corpus
spongiosum of
penis; deep
fascia of penis;
clitoris in
female
Veins of
penis and
clitoris
Ischium; ischial
rami; pubic
rami
Pubic
symphysis;
corpus
cavernosum
of penis in
male; clitoris in
female
Urethra
Ischial rami;
pubic rami
Male; median
raphe.
Female;
vaginal wall
Perineal body
External anal
Anus
Anococcygeal
sphincter
ligament
Muscles that Position to Pelvic Girdle
Muscles that position the pectoral girdle are located either on the anterior thorax
or on the posterior thorax. The anterior muscles include the subclavius, pectoralis minor,
and serratus anterior. The posterior muscles include the trapezius, rhomboid major, and
rhomboid minor.
Muscle
Movement
Target
Origin
Insertion
Subclavius
Stabilizes clavicle
Clavicle
First rib
Inferior
during movement by
surface of
depressing it
clavicle
Pectoralis
Rotates shoulder
Scapula;
Anterior
Coracoid
minor
anteriorly (throwing
ribs
surfaces of
process of
motion); assists with
certain ribs
scapula
inhalation
(2–4 or 3–5)
Serratus
Moves arm from side of Scapula;
Muscle
Anterior surface
anterior
body to front of
ribs
slips from
of vertebral
body; assists with
certain ribs
border of
inhalation
(1–8 or 1–9)
scapula
Muscles that Move the Humerus
Similar to the muscles that position the pectoral girdle, muscles that cross the
shoulder joint and move the humerus bone of the arm include both axial and scapular
muscles. The two axial muscles are the pectoralis major and the latissimus dorsi. The
pectoralis major is thick and fan-shaped, covering much of the superior portion of the
anterior thorax. The broad, triangular latissimus dorsi is located on the inferior part of the
back, where it inserts into a thick connective tissue sheath called an aponeurosis.
Muscle
Movement
Target
Origin
Insertion
Axial Muscles
Pectoralis
Brings
elbows Humerus
Clavicle;
Greater
major
together; moves
sternum;
tubercle
of
the elbow up
cartilage
humerus
during an upper
certain ribs
cut punch
(1-6 or 1-7);
aponeurosis
of external
oblique
muscle
Latissimus
Moves
elbow Humerus; scapula Thoracic
Intertubercular
dorsi
back(
as
in
vertebrae
sulcus
of
elbowing
(T7-T12);
humerus
someone
lumbar
standing behind
vertebrae;
you);
spread
lower ribs (9elbows apart
12);
iliac
crest
Scapular Muscles
Deltoid
Lift
arms
at Humerus
Trapezius;
Deltoid
shoulder
clavicle;
tuberosity of
acromion;
humerus
spine
of
scapula
Subscapularis Assists pectoralis Humerus
Subscapular Lesser tubercle
major in bringing
fossa
and of humerus
elbows together
scapula
and
stabilizes
shoulder
joint
during
movement of the
pectoral girdle
Supraspinatus Rotates elbows Humerus
Supraspinous Greater
outward,
as
fossa
of tubercle
of
during a tennis
scapula
humerus
swing(abduction)
Infraspinatus
Teres Major
Teres Minor
Coracobra
chialis
Rotates
elbow
outwards,
as
during a tennis
swing(adduction)
Assists
infraspinatus
in
rotating
the
elbow outward
Assists
infraspinatus
in
rotating
elbow
outward
Moves elbow up
and across body,
as when putting
hand on chest
Humerus
Infraspinous
Greater
fossa
of tubercle
scapula
humerus
of
Humerus
Posterior
surface
scapula
Humerus
Lateral
Greater
border
of tubercle
of
scapular
humerus
surface
Coracoid
Medial surface
process
of of
humerus
scapula
shaft
Humerus
Intertubercular
of sulcus
of
humerus
Muscles that Move the Forearm
The forearm, made of the radius and ulna bones, has four main types of action at
the hinge of the elbow joint: flexion, extension, pronation, and supination. The forearm
flexors include the biceps brachii, brachialis, and brachioradialis. The are the triceps
brachii and anconeus. The pronators are the pronator teres and the pronator quadratus,
and the supinator is the only one that turns the forearm anteriorly. When the forearm
faces anteriorly, it is supinated. When the forearm faces posteriorly, it is pronated.
Muscle
Movement
Target
Origin
Insertion
Anterior muscles (flexion)
Biceps brachii
Performs a bicep Forearm Coracoid process; Radial
curl; also allows
tubercle
above tuberosity
palm of hand to
glenoid cavity
point toward body
while flexing
Brachialis
Forearm Front
of
distal Coronoid
humerus
process of
ulna
Brachioradialis
Assists ans stabilizes Forearm Lateral
Base
of
elbow during bicepsupracondylar ridge styloid
curl motion
at distal end of process of
humerus
radius
Anterior muscles (pronation)
Pronator teres
Turns hand palm- Forearm Medial epicondyle Lateral
down
of
humerus; radius
coronoid process of
ulna
Pronator
Assists in turning Forearm Distal portion of Distal
quadratus
hand palm-down
anterior ulnar shaft
surface
of
anterior
radius
Muscles of the Arm That Move the Wrists, Hands, and Fingers
Wrist, hand, and finger movements are facilitated by two groups of muscles. The
forearm is the origin of the extrinsicmuscles of the hand. The palm is the origin of the
intrinsic muscles of the hand.
Muscle
Movement
Target
Origin
Insertion
Superficial Anterior compartment of forearm
Flexor carpi Bends wrist toward Wrist;hand Medial epicondyle Base of second
radialis
body; tilts hand to
of humerus
and
third
side away from
metacarpals
the body
Palmaris
Assists in bending Wrist
Medial epicondyle Palmar
longus
hand up toward
of humerus
aponeurosis;
shoulder
skin and fascia
of palm
Flexor carpi Assists in bending Wrist; hand Medial epicondyle Pisifiorm;
ulnaris
hand up toward
of
humerus; hamate bones
shoulder; tilts hans
olecranon process; and base of the
to side away from
posterior surface of fifth carpal
the
body;
ulna
stabilizes wrist
Flexor
Bends fingers to Wrist
Medial epicondyle Midial
digitorum
make a fist
fingers (2- of
humerus; phalanges
of
superficialis
5)
coronoid process fingers 2-5
of ulna; shaft of
radius
Deep Anterior Compartment of Forearm
Flexor policis Bends tip of thumb Thumb
Anterior surface of Distal phalanx
longus
radius; interroseuss of thumb
membrane
Flexor
Bends fingers to Wrist;
Coronoid process; Distal
digitorum
make a fist; also fingers
anteromedial
phalanges
of
profundus
bends
wrist
surface of ulna; fingers 2-5
toward body
interroseuss
membrane
Intrinsic Muscles of the Hand
The intrinsic muscles of the hand both originate and insert within it. These muscles
allow your fingers to also make precise movements for actions, such as typing or writing.
These muscles are divided into three groups. The thenar muscles are on the radial aspect
of the palm. The hypothenar muscles are on the medial aspect of the palm, and the
intermediate muscles are midpalmar.
Muscle
Movement
Target
Origin
Insertion
Abductor pollicis Moves
thumb Thumb
brevis
(thenar toward body
muscle)
Opponens
Pollicis(thenar
muscles)
Flexor
pollicis
brevis
(thenar
muscle)
Moves
thumb Thumb
acrosspalm to touch
other fingers
Flexes thumb
Thumb
Adductor
Moves thumb away Thumb
Pollicis
(thenar from body
muscle)
Abductor
Digiti
minimi
(hypothenar
muscle)
Flexor digiti minimi
brevis
(hypothenar
muscle)
Opponens digiti
minimi
Lumbricals
Palmar
interossei
Dorsal
interossei
Moves little finger Little
toward body
finger
Flexor
retinaculum;
and
nearby
carpals
Flexor
retinaculum;
trapezium
Flexor
retinaculum;
trapezium
Capitate
bone; bases
of metacarpals
2–4; front of
Metacarpal 3
Pisiform bone
Flexes little finger
Little
finger
Hamate
bone; flexor
retinaculum
Moves little finger
across palm to touch
thumb
Flexes each finger at
metacarpophalangeal
joints; extends each
finger at
interphalangeal
joints
Adducts and flexes
each finger at
metacarpophalangeal
joints; extends each
finger at
interphalangeal
joints
Little
finger
Hamate
bone; flexor
retinaculum
Palm (lateral
sides of
tendons in
flexor
digitorum
profundus)
Fingers
Fingers
Side of each
metacarpal
that faces
metacarpal
3 (absent
from
metacarpal
3)
Abducts and flexes Fingers
the
three middle fingers
at
Sides of
metacarpals
Lateral base of
Proximal
phalanx
of
thumb
Anterior of first
metacarpal
Lateral base of
Proximal
phalanx
of
thumb
Medial base of
proximal
phalanx
of thumb
Medial side of
Proximal
phalanx
of little finger
Medial side of
proximal
phalanx
of
little finger
Medial side of
fifth
metacarpal
Fingers 2–5
(lateral edges
of extensional
expansions on
first
phalanges)
Extensor
expansion on
first
phalanx
of
each
finger (except
finger 3) on
side
facing finger 3
Both sides of
finger 3; for
each
other finger,
metacarpophalangeal
joints; extends the
three middle fingers
at
interphalangeal
joints
extensor
expansion
over
first
phalanx
on
side opposite
finger 3
Muscles of the Thigh
The body’s center of gravity is in the area of the pelvis. If the center of gravity were
not to remain fixed, standing up would be difficult as well. Therefore, what the leg muscles
lack in range of motion and versatility, they make up for in size and power, facilitating
the body’s stabilization, posture, and movement. Most muscles that insert on the femur
(the thigh bone) and move it, originate on the pelvic girdle. The psoas major and iliacus
make up the iliopsoas group. Some of the largest and most powerful muscles in the body
are the gluteal muscles or gluteal group. The gluteus maximus is the largest; deep to the
gluteus maximus is the gluteus medius, and deep to the gluteus medius is the gluteus
minimus, the smallest of the trio.
Muscle
Movement
Target Origin
Insertion
Iliopsoas goup
Psoas
Raises knee at hip as if Femur Lumber vertebrae Lesser
major
performing
a
knee
(L1 – L5); thoracic trochanter
of
attack; assists lateral
vertebrae (T12)
femur
rotators in twisting thigh
(and
lower
leg)
outward; assists with
bending
over,
maintaining posture
Iliacus
Raises knee at hip as if Femur Iliac fossa; iliac Leseer
performing
a
knee
crest;
lateral trochanter
of
attack; assists lateral
sacrum
femur
rotators in twisting thigh
(and
lower
leg)
outward; assists with
bending
over,
maintaining posture
Gluteal group
Gluteus
Lowers knee and moves Femur Dorsal
ilium; Gluteal
maximus
thigh back, as when
sacrum; coccyx
tuberosity
of
getting ready to kick a
femur; iliotibial
ball
track
Gluteus
Opens thigh, as when Femur Lateral surface of Greater
medius
doing a split
ilium
trochanter
of
femur
Gluteus
minimus
Brings the thighs back Femur
together
Tensor
fascia lata
Assists at raising knee at Femur
hip and opening thighs;
maintains posture by
stabilizing the iliotibial
track, which connects
to the knee
Lateral Rotators
Piriformis
Twist thigh (and lower Femur
leg) outward, maintains
posture by stabilizing
hip joint
Obturator
Twist thigh (and lower Femur
internus
leg) outward, maintains
posture by stabilizing
hip joint
Obturator
externus
Twist thigh (and lower Femur
leg) outward, maintains
posture by stabilizing
hip joint
Superior
gemellus
Twist thigh (and lower Femur
leg) outward, maintains
posture by stabilizing
hip joint
Twist thigh (and lower Femur
leg) outward, maintains
posture by stabilizing
hip joint
Twist thigh (and lower Femur
leg) outward, maintains
posture by stabilizing
hip joint
Inferior
gemellus
Quadratus
femoris
Adductors
Adductor
longus
Adductor
brevis
Brings the thighs back Femur
together; assists with
raising th knee
Brings the thighs back Femur
together; assists with
raising th knee
External surface of Greater
ilium
trochanter
of
femur
Anterior aspect of Iliotibial track
iliac crest; anteriorsuperior iliac spine
Anterolateral
surface of sacrum
Greater
trochanter
femur
Inner surface of
obturator
membrane;
greater
sciatic
notch; margins of
obturator foramen
Outer surface of
obturator
membrane; pubic
and
ischium;
margins
of
obturator foramen
Ischial spine
Greater
trochanter
in
front of piriformis
Ischial tuberosity
Ischial tuberosity
of
Trochanteric
fossa
of
posterior femur
Greater
trochanter
femur
of
Greater
trochanter
femur
of
Trochanteric
crest of femur
Pubis near pubic Linea aspera
symphysis
Body
of
pubis; Linea
aspera;
inferior ramus of above
pubis
adductor longus
Adductor
magnus
Pectineus
Brings the thighs back Femur
together; assists with
raising th knee and
moving the thigh back
Open thighs; assists with Femur
rasing the knee and
turning the thigh (and
lower leg) inward.
Ischial rami; pubic Linea
aspera;
rami;
ischial adductor
tuberosity
tubercle
of
femur
Pectineal line of Lesser
pubis
trochanter
to
linea aspera of
psoterior aspect
of femur
Muscles that Move the Femur, Tibia, and Fibula
Deep fascia in the thigh separates it into medial, anterior, and posterior
compartments. The muscles in the medial compartment of the thigh are responsible for
adducting the femur at the hip. Along with the adductor longus, adductor brevis,
adductor magnus, and pectineus, the strap-like gracilis adducts the thigh in addition to
flexing the leg at the knee.
Muscle
Movement
Target
Origin
Insertion
Medial compartment of thigh
Gracilis
Moves back of lower Femur;
Inferior ramus; body Medial
legs to up toward tibia/fibula of pubis; ischial surface of
buttocks, as when
ramus
tibia
kneeling; assists
in
opening thighs
Anterior compartment of thigh: Quzdriceps femoris group
Rectus
Moves lower leg out Femur;
Anterior/inferior ilias Patellla;
femoris
out in front of body, as tibia, fibula spine;
superior tibial
when kicking; assists in
margin
of tuberosity
raising the knee
accetabulum
Vastus
Moves lower leg out in Tibia/ fibula Greater trochanter; Patella;
lateralis
front of the body, as
intertrochanteric
tibial
when kicking
line; linea spera
tuberosity
Vastus
Moves lower leg out in Tibia/ fibula Linea
spera; Patella;
medialis
front of the body, as
intertrochantic line
tibial
when kicking
tuberosity
Vastus
Moves lower leg out in Tibia/ fibula Proximal femur shaft Patella;
intermedius front of the body, as
tibial
when kicking
tuberosity
Sartorius
Moves back lower legs Femur;
Anterior
superior Medial
up and back towards tibia/fibula iliac spine
aspect of
buttocks, as when
proximal
kneeling; assists in
tibia
moving
thigh
diagonally
upward
and outward as when
mounting a bike
Muscles that Move the Feet and Toes
Similar to the thigh muscles, the muscles of the leg are divided by deep fascia into
compartments, although the leg has three: anterior, lateral, and posterior. The muscles
of the anterior compartment of the lower leg are generally responsible for dorsiflexion,
and the muscles of the posterior compartment of the lower leg are generally responsible
for plantar flexion. The lateral and medial muscles in both compartments invert, evert,
and rotate the foot.
Muscle
Movement
Target
Origin
Insertion
Anterior Compartment of Leg
Tibialis
Raises sole of the foot off Foot
Lateral condyle Interior
anterior
the
groundas
when
and upper tibial surface
of
preparing to foot-tap;
shaft; interosseus medial
bends the inside of the
membrane
cunieform; first
foot upward, as when
metatarsal
catching your balance
bone
when
falling
laterally
toward the opposite side
as the balancing foot
Extensor
Raises the sole fo the foot Foot;
Anteromedial
Distal phalanx
hallucis
off the ground, as when big toe fibula
shaft; of big toe
longus
preparing a foot-tap;
interossues
extends big toe
membrane
Extensor
Raises the sole of the foot Foot;
Lateral condyle Middle
and
digitorum
off the ground, as when big
of tibia; proximal distal
longus
preparing a foot-tap; toes 2-5 portion of fibula; phalanges of
extends toes
interosseus
toes 2-5
membrane
Lateral Compartment of Leg
Fibulari
Lowers the sole of the foot Foot
Upper portion of First
longus
to the ground; as when
lateral fibula
metatarsal;
foot-tapping or jumping;
medial
bends the inside of the
cunieform
foot downwards as when
catching your balance
while
falling
laterally
toward the same side as
the balancing foot
Fibularis
Lowers the sole of the foot Foot
Distal fibula shaft Proximal end
(peroneus) to the ground; as when
of the fifth
brevis
foot-tapping or jumping;
metatarsal
bends the inside of the
foot downwards as when
catching your balance
while
falling
laterally
toward the same side as
the balancing foot
Intrinsic Muscles of the Foot
The muscles along the dorsal side of the foot generally extend the toes while the
muscles of the plantar side of the foot generally flex the toes. The plantar muscles exist in
three layers, providing the foot the strength to counterbalance the weight of the body.
Muscles
Movement
Target Origin
Insertion
Dorsal Group
Extensor
Extends toes 2-5
Toes 2- Calcaneus;
Base of proximal
digitorum
5
extensor
phalanx of bif
brevis
retinaculum
toe;
extensor
expansions
in
toes 2-5
Plantar Group (layer 1)
Abductor
Abducts and flexes big Big toe Calcaneal
Proximal phalanx
hallucis
toe
tuberosity; flexor of big toe
retinaculum
Flexor
Flexes toe 2-4
Middle Calcaneal
Middle phalanx
digitorun
toes
tuberosity
of toes 2-4
brevis
Abductor
Abducts and flexes Toe 5
Calcaneal
Proximal phalanx
digiti minimi little toe
tuberosity
of little toe
Plantar group (layer 2)
Quadratus
Assists in flexing toes 2- Toes 2- Medial and lateral Tendon of flexor
plantae
5
5
side of calcaneus digitorum longus
Lumbricals
Extends toes 2-5 at the Toes 2- Tendond of flexor Medial side of
interphalangeal joints; 5
digitorum longus
proximal phalanx
flexes the small toe at
toes 2-5
the
metatarsophalangeal joints
Plantar Group (layer 3)
Flexor
Flexes big toe
Bigt
Lateral cunieform;
hallucis
toe
cuboid bones
brevis
Adductor
Adducts and flexes big Big
Bases
of
longus
toe
toe
metatarsals 2-4;
fibularis
longus
tendon
sheath;
ligament across
metatarsophalangeal joints
Flexor digiti Flexes small toe
Little
Base
of Base of proximal
minimi
toe
metatarsal
5; phalanx of little
brevis
tendon sheath of toe
fibularis longus
Plantar Group (layer 4)
Dorsal
interossei
Abducts and flexes the Middle
middle
toe
at toes
metatarso-phalangeal
joints; extends middle
toes
at
interphalangeal joints
Plantar
interossei
Abducts
toes
3-5; Small
flexes
proximal toes
phalanges
and
extends
distal
phalanges
Sides
metatarsals
of Both sides of toe
2; ofr each other
toe,
extensor
expansion over
first phalanx on
side of opposite
toe 2
Side
of
each Extensor
metatarsal
that expansion on first
faces metatarsal phalanx of each
2 ( absent in toe (except for 2)
metatarsal 2)
on side facing
toe 2
Posterior Skeletal Muscle
Muscles that Move the Head
The head, attached to the top of the vertebral column, is balanced, moved, and
rotated by the neck muscles. When these muscles act unilaterally, the head rotates.
When they contract bilaterally, the head flexes or extends. The major muscle that laterally
flexes and rotates the head is the sternocleidomastoid.
Muscle
Movement
Target
Origin
Insertion
Sternocleidomastoid Rotates and
Skull;
Sternum; clavicle
Temporal
tilts head to the vertebrae
Bone
side; tilts head
(mastoid
forward
process);
occipital
bone
Semispinalis capitis
Rotates and
Skull;
Transverse
and Occipital
tilts head
vertebrae articular processes bone
backward
of cervical and
Thoracic vertebra
Splenius capitis
Rotates and
Skull;
Spinous processes Temporal
tilts head to the vertebrae of cervical and
Bone
side; tilts head
thoracic vertebra
(mastoid
backward
process);
occipital
bone
Longissimus capitis
Rotates and
Skull;
Transverse
and Temporal
tilts head to the vertebrae articular processes bone
side; tilts head
Of cervical and (mastoid
backward
thoracic vertebra
process)
Muscles of the Posterior Neck and Back
The posterior muscles of the neck are primarily concerned with head movements,
like extension. The back muscles stabilize and move the vertebral column, and are
grouped according to the lengths and direction of the fascicles. The splenius muscles
originate at the midline and run laterally and superiorly to their insertions. From the sides
and the back of the neck, the splenius capitis inserts onto the head region, and the
splenius cervicis extends onto the cervical region. These muscles can extend the head,
laterally flex it, and rotate it.
The erector spinae group forms the majority of the muscle mass of the back and it
is the primary extensor of the vertebral column. It controls flexion, lateral flexion, and
rotation of the vertebral column, and maintains the lumbar curve. The erector spinae
comprises the iliocostalis (laterally placed) group, the longissimus (intermediately
placed) group, and the spinalis (medially placed) group.
The iliocostalis group includes the;
a. iliocostalis cervicis, associated with the cervical region;
b. iliocostalis thoracis,associated with the thoracic region; and
c. iliocostalis lumborum, associated with the lumbar region.
The three musclesof the longissimus group are the
a. longissimus capitis, associated with the head region;
b. longissimus cervicis, associated with the cervical region; and
c. longissimus thoracis, associated with the thoracic region.
The third group, the spinalis group, comprises the;
a. spinalis capitis (head region),
b. spinalis cervicis (cervical region), and
c. spinalis thoracis (thoracic region).
The transversospinales muscles run from the transverse processes to the spinous
processes of the vertebrae. Similar to the erector spinae muscles, the semispinalis
muscles in this group are named for the areas of the body with which they are
associated. The semispinalis muscles include the;
a.
semispinalis capitis
b.
semispinalis cervicis
c.
semispinalis thoracis
Muscle that Position the Pectoral Girdle
Muscle
Movement
Trapezius
Elevates shoulders
(shrugging); pulls shoulder
blades
together; tilts head
backwards
Rhomboid Stabilizes scapula
major
during pectoral girdle
movement
Rhomboid Stabilizes scapula
minor
during pectoral girdle
movement
Target
Scapula;
Cervical
spine
Origin
Skull;
Vertebral
column
Insertion
Acromion
and spine of
scapula;
clavicle
Scapula
Thoracic
vertebrae
(T2–T5)
Cervical and
Thoracic
vertebrae
(C7 and T1)
Medial
border of
scapula
Medial border
of scapula
Scapula
Muscles that Move the Forearm
Muscle
Movement
Posterior muscle (extension)
Triceps
Extends forearm,
brachii
as during a punch
Anconeus
Assists in extending
forearm; also
allows forearm to
extend away from
the body
Posterior muscle (supination)
Supinator
Turns hand palmup
Target
Origin
Insertion
Forearm
Infraglenoid tubercle of
scapula; posterior shaft
of humerus; posterior
humeral shaft distal to
the radial groove
Lateral epicondyle of
humerus
Ocleranon
process of
ulna
Lateral epicondyle of
humerus; proximal ulna
Proximal end
of radius
Forearm
Forearm
Muscles of the Arm That Move the Wrists, Hands, and Fingers
Muscle
Movement
Target
Origin
Superficial posterior compartment of forearm
Extensor
Straightens wrist
Wrist
Lateral
radialis
away from body; tilts
supracondylar
longus
hand to side away
ridge of humerus
from body
Extensor
Assists extensor
Wrist
Lateral epicondyle
carpi
radialis longus in
of humerus
radialis
extending and
brevis
abducting wrist; also
stabilizes hand during
finger flexion
Extensor
Opens fingers and
Wrist;
Lateral epicondyle
digitorum
moves them
fingers
of humerus
sideways away from
the body
Extensor
Extends little finger
Little
Lateral epicondyle
digiti
finger
of humerus
minimi
Extensor
carpi
ulnaris
Straightens wrist
Wrist
away from body; tilts
hand to side toward
body
Deep posterior compartment of forearm
Abductor
Moves thumds
Wrist;
pollicis
sideways toward
thumb
longus
body; extends
Lateral epicondyle
of humerus;
posterior border of
ulna
Posterior surface of
radius and ulna;
Lateral aspect
of ocleranon
process of
ulna
Insertion
Base of second
metacarpal
Base of third
metacarpal
Extensor
expansions;
distal phalanges
of fingers
Extensor
expansions;
distal phalanx of
finger 5
Base of fifth
metacarpal
Base of first
metacarpal;
trapezium
thumb; moves hand
sideways toward the
body
Extends thumb
Thumb
Extensor
pollicis
longus
Extends thumb
Thumb
Extensor
indicis
Extends index finger;
straightens wrist
away from body
Wrist;
index
finger
Extensor
pollicis
brevis
interosseus
membrane
Dorsal shaft of
radius and ulna;
interossues
membrane
Dorsal shaft of
radius and ulna;
interossues
membrane
Posterior surface of
distal ulna;
interossues
membrane
Base of proximal
phalanx of
thumb
Base of proximal
phalanx of
thumb
Tendon extensor
digitorum of
index finger
Muscles that Move the Femur, Tibia, and Fibula
Muscle
Movement
Target
Origin
Insertion
Posterior compartment of thigh; Hamstring group
Biceps femoris
Moves back of lower
Femur;
Ischial
Head of
legs up and back
tibia/fibula tuberosity;
fibula;
toward the buttocks, as
linea aspera; lateral
when kneeling; moves
distal femur
condyle of
thigh down and back;
tibia
twist the thigh (and
lower leg) outward
Semitendinosus Moves back of lower
Femur;
Ischial
Upper tibial
legs up and back
tibia/fibula tuberosity
shaft
toward the buttocks, as
when kneeling; moves
thigh down and back;
twist the thigh (and
lower leg) inward
Semi- membra- Moves back of lower
Femur;
Ischial
Medial
nous
legs up and back
tibia/fibula tubeorsity
condyle of
toward the buttocks, as
tibia; lateral
when kneeling; moves
condyle of
thigh down and back;
femur
twist the thigh (and
lower leg) inward
Muscles that Move the Feet and Toes
Muscle
Movement
Target
Origin
Insertion
Posterior compartment of leg: Superficial muscle
Gastronecmius
Lower the sole of the
Foot;
Medial and
Posterior
foot to the ground, as tibia/fibula lateral
calcaneus
when foot tapping or
jumping; asssist in
moving the back of
the lower legs up and
back towards the
buttocks
Soleus
Lowers the sole of the
Foot
foot to the ground, as
when foot-tapping or
jumping; maintains
posture while walking
Plantaris
Lowers the sole of the
Foot;
foot to the ground, as tibia/fibula
when foot-tapping or
jumping; assists in
moving the back of
the lower leg up and
toward the buttocks
Tibialis posterior Lowers the sole of the
Foot
foot to the ground, as
when foot-tapping or
jumping
Posterior compartment of leg: Deep muscle
Popliteus
Moves back of the
Tibia/fibula
lower legs up and
back toward the
buttocks; assists in the
rotation of leg at the
knee and thigh
Flexor digitorum Lowers the sole of the
Foot; toes
longus
foot to the ground as
2-5
when foot-tapping or
jumping; bends the
inside of the foot
upward and flexes
toes
Flexor hallucis
Flexes the big toe
Big toe;
longus
foot
condyles of
femur
Superior
tiba;fibula;
interossues
membrane
Posterior
calcaneus
Posterior
femur above
lateral
condyle
Calcaneus
or calcaneus
tendon
Tibialis
posterior
Several
tarsals and
metatarsals
2-4
Lateral
condyle of
femur; lateral
meniscus
Proximal tibia
Posterior tibia
Distal
phalanges of
toes 2-5
Midshaft of
fibula;
interossues
membrane
Distal
pahalanx of
big toe
Histology of Muscle Tissue
Muscle is one of the four primary tissue types of the body, and the body contains
three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. All
three muscle tissues have some properties in common; they all exhibit a quality called
excitability as their plasma membranes can change their electrical states (from polarized
to depolarized) and send an electrical wave called an action potential along the entire
length of the membrane. While the nervous system can influence the excitability of
cardiac and smooth muscle to some degree, skeletal muscle completely
depends on signaling from the nervous system to work properly. On the other hand, both
cardiac muscle and smooth muscle can respond to other stimuli, such as hormones and
local stimuli.
Levels of Biological Organization within Skeletal Muscle
Skeletal muscle
Organ made up of fascicles that contain muscle fi bers (cells),
blood vessels, and nerves; wrapped in epimysium.
Facsicle
Bundle of muscle fi bers wrapped in perimysium.
Muscle fiber (cell)
Long cylindrical cell covered by endomysium and
sarcolemma; contains
sarcoplasm, myofi brils, many peripherally located nuclei,
mitochondria,
transverse tubules, sarcoplasmic reticulum, and terminal
cisterns. The fiber has a striated appearance.
Threadlike contractile elements within sarcoplasm of muscle
fiber that extend entire length of fi ber; composed of
filaments.
Contractile proteins within myofi brils that are of two types:
thick fi laments
composed of myosin and thin fi laments composed of actin,
tropomyosin,
and troponin; sliding of thin fi laments past thick fi laments
produces muscle
shortening.
Myofibril
Filaments
(myofilaments)
Components of Sarcomere
1. Z discs - Narrow, plate-shaped regions of dense material that separate one
sarcomere from the next.
2. A band - Dark, middle part of sarcomere that extends entire length of thick
filaments and includes those parts of thin fi laments that overlap thick filaments.
3. I band - Lighter, less dense area of sarcomere that contains remainder of thin
filaments but no thick fi laments. A Z disc passes through center of each I band.
4. H zone - Narrow region in center of each A band that contains thick filaments
but no thin fi laments.
5. M line - Region in center of H zone that contains proteins that hold thick
filaments together at center of sarcomere.
Muscle Proteins
Contractile Proteins - Proteins that generate force during muscle contractions.
Myosin
Contractile protein that makes up thick fi lament; molecule consists of
a tail and two myosin heads, which bind to myosin binding sites on
actin molecules of thin fi lament during muscle contraction.
Actin
Contractile protein that is the main component of thin fi lament; each
actin molecule has a myosin-binding site where myosin
head of thick fi lament binds during muscle contraction.
Regulatory Proteins - Proteins that help switch muscle contraction process on and off.
Tropomyosin Regulatory protein that is a component of thin fi lament; when skeletal
muscle fi ber is relaxed, tropomyosin covers myosin binding sites on
actin molecules, thereby preventing myosin from binding to actin.
Troponin
Regulatory protein that is a component of thin fi lament; when
calcium ions (Ca2) bind to troponin, it changes shape; this
conformational change moves tropomyosin away from myosinbinding sites on actin molecules, and muscle contraction
subsequently begins as myosin binds to actin.
Structural Proteins - Proteins that keep thick and thin fi laments of myofi brils in proper
alignment, give myofi brils elasticity and extensibility, and link myofi brils to
sarcolemma and extracellular matrix.
Titin
Structural protein that connects Z disc to M line of sarcomere, thereby
helping to stabilize thick fi lament position; can stretch and then spring
back unharmed, and thus accounts for much of the elasticity and
extensibility of myofi brils.
Structural protein that forms M line of sarcomere; binds to titin
α- Actinin
molecules and connects adjacent thick fi laments to one another.
Nebulin
Structural protein that wraps around entire length of each thin fi
lament; helps anchor thin fi laments to Z discs and regulates
length of thin fi laments during development.
Dystrophin
Structural protein that links thin fi laments of sarcomere to integral
membrane proteins in sarcolemma, which are attached
in turn to proteins in connective tissue matrix that surrounds muscle fi
bers; thought to help reinforce sarcolemma and help
transmit tension generated by sarcomeres to tendons.
Contraction and Relaxation of Skeletal Muscle Fibers
Researchers discovered that skeletal muscle shortens during contraction because
the thick and thin filaments slide past one another. The model describing this process is
known as the sliding filament mechanism.
The Sliding Filament Mechanism
Muscle contraction occurs because myosin heads attach to and “walk” along the
thin filaments at both ends of a sarcomere, progressively pulling the thin filaments toward
the M line. As a result, the thin filaments slide inward and meet at the center of a
sarcomere. They may even move so far inward that their ends overlap. As the thin
filaments slide inward, the I band and H zone narrow and eventually disappear
altogether when the muscle is maximally contracted. However, the width of the A band
and the individual lengths of the thick and thin filaments remain unchanged. Since the
thin filaments on each side of the sarcomere are attached to Z discs, when the thin
filaments slide inward, the Z discs come closer together, and the sarcomere shortens.
Shortening of the sarcomeres causes shortening of the whole muscle fiber, which in turn
leads to shortening of the entire muscle.
The Contraction Cycle
At the onset of contraction, the sarcoplasmic reticulum releases calcium ions
(Ca2) into the sarcoplasm. There, they bind to troponin. Troponin then moves
tropomyosin away from the myosin binding sites on actin. Once the binding sites are
“free,” the con traction cycle—the repeating sequence of events that causes
the filaments to slide—begins. The contraction cycle consists of four steps.
1. ATP hydrolysis. The myosin head includes an ATP-binding site and an
ATPase, an enzyme that hydrolyzes ATP into ADP (adenosine diphosphate)
and a phosphate group. This hydrolysis reaction reorients and energizes
the myosin head. Notice that the products of ATP hydrolysis—ADP and a
phosphate group—are still attached to the myosin head.
2. Attachment of myosin to actin to form cross-bridges. The energized
myosin head attaches to the myosin-binding site on actin and releases
the previously hydrolyzed phosphate group. When the myosin heads
attach to actin during contraction, they are referred to as cross-bridges.
3. Power stroke. After the cross-bridges form, the power stroke occurs. During
the power stroke, the site on the cross-bridge where ADP is still bound
opens. As a result, the cross-bridge rotates and releases the ADP. The
cross-bridge generates force as it rotates toward the center of the
sarcomere, sliding the thin filament past the thick filament toward the M
line.
4. Detachment of myosin from actin. At the end of the power stroke, the
cross-bridge remains firmly attached to actin until it binds another
molecule of ATP. As ATP binds to the ATP-binding site on the myosin head,
the myosin head detaches from actin.
UNIVERSITY OF CALOOCAN CITY
Biglang Awa St., Corner Catleya St., EDSA, Caloocan City
COLLEGE OF EDUCATION
Anatomy and Physiology
SUBJECT CODE:
TOPIC OR LESSON:
WEEK:
SUB-TOPIC/S:
MBS 313
Endocrine and Merocrine Gland
8
1. Thyroid Gland
2. Merocrine/Mammary Gland
OVERVIEW OF THE TOPIC
Communication is a process in which a sender transmits signals to one or more
receivers to control and coordinate actions. In the human body, two major organ systems
participate in relatively “long distance” communication: the nervous system
and the endocrine system. Together, these two systems are primarily responsible for
maintaining homeostasis in the body.
Different glands secrete different hormones and each hormone affects the
human body. For example, in girls, estrogens promote accumulation of adipose tissue in
the breasts and hips, sculpting a feminine shape. At the same time or a little later,
increasing levels of testosterone in boys begin to help build muscle mass and enlarge the
vocal cords, producing a lower-pitched voice. These changes are just a few examples
of the powerful influence of endocrine secretions. Less dramatically, perhaps, multitudes
of hormones help maintain homeostasis on a daily basis. They regulate the activity of
smooth muscle, cardiac muscle, and some glands; alter metabolism; spur growth and
development; influence reproductive processes; and participate in circadian (daily)
rhythms established by the suprachiasmatic nucleus of the hypothalamus.
a.
Name the different glands on the Endocrine System;
b.
Identify the hormones secreted by each gland and describe how it affects
the body; and
c.
Present common ailments of the thyroid gland, its causes, symptoms,
treatments, and prevention measures.
At the end of this module, students should be able to:
a.
identify the different glands and hormones of the Endocrine System;
b.
c.
discuss the characteristics and importance of thyroid gland; and
discuss the characteristics of mammary gland.
Endocrine System
The endocrine system uses just one method of communication: chemical
signaling. These signals are sent by the endocrine organs, which secrete chemicals—the
hormone—into the extracellular fluid. Hormones are transported primarily via the
bloodstream throughout the body, where they bind to receptors on target cells, inducing
a characteristic response. As a result, endocrine signaling requires more time than neural
signaling to prompt a response in target cells, though the precise amount of time varies
with different hormones.
In addition, endocrine signaling is typically less specific than neural signaling. The
same hormone may play a role in a variety of different physiological processes
depending on the target cells involved. For example, the hormone oxytocin promotes
uterine contractions in women in labor. It is also important in breastfeeding and may be
involved in the sexual response and in feelings of emotional attachment in both males
and females.
Endocrine System
Nervous System
Signaling mechanism(s)
Chemical
Chemical/electrical
Primary chemical signal
Hormones
Neurotransmitters
Distance traveled
Long or short
Always short
Response time
Fast or slow
Always fast
Environment targeted
Internal
Internal and external
Endocrine Glands
Endocrine glands (endo- within) secrete their products (hormones) into the
interstitial fluid surrounding the secretory cells rather than into ducts. From the interstitial
fluid, hormones diffuse into blood capillaries and blood carries them to target cells
throughout the body. Because of their dependence on the cardiovascular system to
distribute their products, endocrine glands are some of the most vascular tissues of the
body. Considering that most hormones are required in very small amounts, circulating
levels typically are low.
The endocrine glands include the pituitary, thyroid, parathyroid, adrenal, and
pineal glands. In addition, several organs and tissues are not exclusively classified as
endocrine glands but contain cells that secrete hormones. These include the
hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine,
skin, heart, adipose tissue, and placenta. Taken together, all endocrine glands and
hormone-secreting cells constitute the endocrine system.
Hormones
A hormone (hormone- to excite or get moving) is a mediator molecule that is
released in one part of the body but regulates the activity of cells in other parts of the
body. Most hormones enter interstitial fluid and then the bloodstream. The circulating
blood delivers hormones to cells throughout the body. Both neurotransmitters and
hormones exert their effects by binding to receptors on or in their “target” cells.
Chemical Classes of Hormones
The hormones of the human body can be divided into two major groups on the
basis of their chemical structure. Hormones derived from amino acids include amines,
peptides, and proteins. Those derived from lipids include steroids. These chemical groups
affect a hormone’s distribution, the type of receptors it binds to, and other aspects of its
function.
1. Amine Hormones - Are hormones derived from the modification of amino
acids. Typically, the original structure of the amino acid is modified such
that a –COOH, or carboxyl, group is removed, whereas the −NH3+, or
amine, group remains.
2. Peptide and Protein Hormones - peptide and protein hormones consist of
multiple amino acids that link to form an amino acid chain. Peptide
hormones consist of short chains of amino acids, whereas protein hormones
are longer polypeptides. Both types are synthesized like other body
proteins: DNA is transcribed into mRNA, which is translated into an amino
acid chain.
3. Steroid Hormones- Steroid hormones are derived from the lipid cholesterol.
For example, the reproductive hormones testosterone and the estrogens—
which are produced by the gonads (testes and ovaries)—are steroid
hormones. The adrenal glands produce the steroid hormone aldosterone,
which is involved in osmoregulation, and cortisol, which plays a role in
metabolism.
Action of Lipid- Soluble Hormone
Steroid hormones and thyroid hormones bind to receptors within target cells. Their
mechanism of action is as follows.
1. A free lipid-soluble hormone molecule diffuses from the blood, through
interstitial fluid, and through the lipid bilayer of the plasma membrane into
a cell.
2. If the cell is a target cell, the hormone binds to and activates receptors
located within the cytosol or nucleus. The activated receptor–hormone
complex then alters gene expression: It turns specific genes of the nuclear
DNA on or off.
3. As the DNA is transcribed, new messenger RNA (mRNA) forms, leaves the
nucleus, and enters the cytosol. There, it directs synthesis of a new protein,
often an enzyme, on the ribosomes.
4. The new proteins alter the cell’s activity and cause the responses typical of
that hormone.
Action of Water- Soluble Hormone
Water-soluble hormones bind to receptors that protrude from the target-cell
surface. The receptors are integral transmembrane proteins in the plasma membrane.
When a water-soluble hormone binds to its receptor at the outer surface of the plasma
membrane, it acts as the first messenger. The first messenger (the hormone) then causes
production of a second messenger inside the cell, where specific hormone-stimulated
responses take place. One common second messenger is cyclic AMP (cAMP).
Neurotransmitters, neuropeptides, and several sensory transduction mechanisms also act
via second-messenger systems. The action of a typical water-soluble hormone occurs as
follows.
1. A water-soluble hormone (the first messenger) diffuses from the blood through
interstitial fluid and then binds to its receptor at the exterior surface of a target
cell’s plasma membrane. The hormone–receptor complex activates a
membrane protein called a G protein. The activated G protein in turn
activates adenylate cyclase.
2. Adenylate cyclase converts ATP into cyclic AMP (cAMP). Because the
enzyme’s active site is on the inner surface of the plasma membrane, this
reaction occurs in the cytosol of the cell.
3. Cyclic AMP (the second messenger) activates one or more protein kinases,
which may be free in the cytosol or bound to the plasma membrane. A protein
kinase is an enzyme that phosphorylates (adds a phosphate group to) other
cellular proteins (such as enzymes). The donor of the phosphate group is ATP,
which is converted to ADP.
4. Activated protein kinases phosphorylate one or more cellular proteins.
Phosphorylation activates some of these proteins and inactivates others, rather
like turning a switch on or off.
5. Phosphorylated proteins in turn cause reactions that produce physiological
responses. Different protein kinases exist within different target cells and within
different organelles of the same target cell.
6. After a brief period, an enzyme called phosphodiesterase inactivates cAMP.
Thus, the cell’s response is turned off unless new hormone molecules continue
to bind to their receptors in the plasma membrane.
Hormone Interaction
Two or more hormones can interact to affect the response of cells in a variety of
ways. The three most common types of interaction are as follows:
A.
The permissive effect, in which the presence of one hormone enables another
hormone to act. For example, thyroid hormones have complex permissive relationships
with certain reproductive hormones. A dietary deficiency of iodine, a component of
thyroid hormones, can therefore affect reproductive system development and
functioning.
B.
The synergistic effect, in which two hormones with similar effects produce an
amplified response. In some cases, two hormones are required for an adequate
response. For example, two different reproductive hormones—FSH from the pituitary
gland and estrogens from the ovaries—are required for the maturation of female ova
(egg cells).
C.
The antagonistic effect, in which two hormones have opposing effects. A familiar
example is the effect of two pancreatic hormones, insulin and glucagon. Insulin increases
the liver’s storage of glucose as glycogen, decreasing blood glucose, whereas glucagon
stimulates the breakdown of glycogen stores, increasing blood glucose.
Hormone Regulation
1. Positive feedback loops are characterized by the release of additional
hormone in response to an original hormone release.
Example: The release of oxytocin during childbirth is a positive feedback loop.
The initial release of oxytocin begins to signal the uterine muscles to contract,
which pushes the fetus toward the cervix, causing it to stretch. This, in turn,
signals the pituitary gland to release more oxytocin, causing labor contractions
to intensify. The release of oxytocin decreases after the birth of the child.
2.
Negative feedback is characterized by the inhibition of further secretion of a
hormone in response to adequate levels of that hormone. This allows blood levels of the
hormone to be regulated within a narrow range.
Example: An example of a negative feedback loop is the release of
glucocorticoid hormones from the adrenal glands, as directed by the
hypothalamus and pituitary gland. As glucocorticoid concentrations in the
blood rise, the hypothalamus and pituitary gland reduce their signaling to the
adrenal glands to prevent additional glucocorticoid secretion.
Endocrine Glands and Their Major Hormones
Endocrine
gland
Pituitary
(anterior)
Pituitary
(anterior)
Pituitary
(anterior)
Pituitary
(anterior)
Pituitary
(posterior)
Pituitary
(posterior)
Thyroid
Thyroid
Parathyroid
Adrenal
(cortex)
Adrenal
(cortex)
Adrenal
(medulla)
Pineal
Pancreas
Associated
hormones
Thyroid-stimulating
hormone (TSH)
Adrenocorticotropic
hormone (ACTH)
Follicle-stimulating
Hormone (FSH)
Glycoprotein Stimulates
gamete production
Luteinizing hormone
(LH)
Antidiuretic hormone
(ADH)
Oxytocin
Chemical
class
Glycoprotein
Effect
Glycoprotein
Thyroxine (T4),
triiodothyronine (T3)
Calcitonin
Parathyroid
hormone (PTH)
Aldosterone
Amine
Stimulates androgen
production by gonads
Stimulates water
reabsorption by kidneys
Stimulates uterine
contractions during
childbirth
Stimulate basal metabolic
rate
Reduces blood Ca2+ levels
Increases blood Ca2+
levels
Increases blood Na+
levels
Increase blood glucose
levels
Cortisol,
corticosterone,
cortisone
Epinephrine,
norepinephrine
Melatonin
Insulin
Stimulates thyroid hormone
release
Peptide
Stimulates hormone release
by adrenal cortex
Glycoprotein
Stimulates gamete
production
Peptide
Peptide
Peptide
Peptide
Steroid
Steroid
Amine
Amine
Protein
Stimulate fight-or-flight
response
Regulates sleep cycles
Reduces blood glucose
levels
Pancreas
Glucagon
Protein
Testes
Testosterone
Steroid
Ovaries
Estrogens and
progesterone
Steroid
Increases blood glucose
levels
Stimulates development of
male secondary sex
characteristics and sperm
production
Stimulate development of
female secondary sex
characteristics and
prepare the body for
childbirth
The Hypothalamus
The hypothalamus responds to a variety of signals from the internal and external
environment including body temperature, hunger, feelings of being full up after eating,
blood pressure and levels of hormones in the circulation. The hormones secreted by the
hypothalamus are as follows.
Hormone
Effect
CorticotrophinThe main element that drives the body's response to stress. It is
releasing hormone
also present in diseases that cause inflammation. Too much or
too little corticotrophin-releasing hormone can have a range
of negative effects.
Growth
hormone- Stimulates the secretion of growth hormone, an important
releasing hormone
regulator of growth, metabolism, and body structure.
Somatostatin
Hormone that inhibits the secretion of several other hormones,
including growth hormone, thyroid stimulating hormone,
cholecystokinin and insulin.
GonadotrophinReleased from nerve cells in the brain. It controls the production
releasing hormone
of luteinizing hormone and follicle stimulating hormone from the
pituitary gland.
Thyrotropin-releasing Produced by the hypothalamus. It plays an important role in the
hormone
regulation of thyroid gland activity.
Dopamine
Inhibits the release of prolactin from the anterior pituitary. Also
inhibits the release of Melanocyte-stimulating hormone (MSH)
Thyroid Gland
The thyroid gland is located anterior to the trachea, just inferior to the larynx . The
medial region, called the isthmus, is flanked by wing-shaped left and right lobes. Each of
the thyroid lobes are embedded with parathyroid glands, primarily on their posterior
surfaces. The tissue of the thyroid gland is composed mostly of thyroid follicles. The follicles
are made up of a central cavity filled with a sticky fluid called colloid. Surrounded by a
wall of epithelial follicle cells, the colloid is the center of thyroid hormone production, and
that production is dependent on the hormones’ essential and unique component:
iodine.
Formation, Storage, and Release of Thyroid Hormones
The thyroid gland is the only endocrine gland that stores its secretory product in
large quantities—normally about a 100-day supply. Synthesis and secretion of T3 and T4
occurs as follows.
1. Iodide trapping. Thyroid follicular cells trap iodide ions (Iˉ) by actively
transporting them from the blood into the cytosol. As a result, the thyroid gland
normally contains most of the iodide in the body.
2. Synthesis of thyroglobulin. While the follicular cells are trapping Iˉ, they are also
synthesizing thyroglobulin (TGB), a large glycoprotein that is produced in the
rough endoplasmic reticulum, modified in the Golgi complex, and packaged
into secretory vesicles. The vesicles then undergo exocytosis, which releases
TGB into the lumen of the follicle.
3. Oxidation of iodide. Some of the amino acids in TGB are tyrosine that will
become iodinated. However, negatively charged iodide ions cannot bind to
tyrosine until they undergo oxidation (removal of electrons) to iodine: 2 Iˉ → I2.
As the iodide ions are being oxidized, they pass through the membrane into
the lumen of the follicle.
4. Iodination of tyrosine. As iodine molecules (I2) form, they react with tyrosine
that are part of thyroglobulin molecules. Binding of one iodine atom yields
monoiodotyrosine (T1), and a second iodination produces diiodotyrosine (T2).
The TGB with attached iodine atoms, a sticky material that accumulates and
is stored in the lumen of the thyroid follicle, is termed colloid.
5. Coupling of T1 and T2. During the last step in the synthesis of thyroid hormone,
two T2 molecules join to form T4, or one T1 and one T2 join to form T3.
6. Pinocytosis and digestion of colloid. Droplets of colloid reenter follicular cells
by pinocytosis and merge with lysosomes. Digestive enzymes in the lysosomes
break down TGB, cleaving off molecules of T3 and T4.
7. Secretion of thyroid hormones. Because T3 and T4 are lipid soluble, they diffuse
through the plasma membrane into interstitial fluid and then into the blood. T4
normally is secreted in greater quantity than T3, but T3 is several times more
potent. Moreover, after T4 enters a body cell, most of it is converted to T3 by
removal of one iodine.
8. Transport in the blood. More than 99% of both the T3 and the T4 combine with
transport proteins in the blood, mainly thyroxine-binding globulin (TBG).
Regulation of TH Synthesis
The release of T3 and T4 from the thyroid gland is regulated by thyroid-stimulating
hormone (TSH). Low blood levels of T3 and T4 stimulate the release of thyrotropinreleasing hormone (TRH) from the hypothalamus which triggers secretion of TSH from the
anterior pituitary. In turn, TSH stimulates the thyroid gland to secrete T3 and T4. The levels
of TRH, TSH, T3, and T4 are regulated by a negative feedback system in which increasing
levels of T3 and T4 decrease the production and secretion of TSH.
Functions of Thyroid Hormones
The thyroid hormones, T3 and T4, are often referred to as metabolic hormones
because their levels influence the body’s basal metabolic rate, the amount of energy
used by the body at rest. When T3 and T4 bind to intracellular receptors located on the
mitochondria, they cause an increase in nutrient breakdown and the use of oxygen to
produce ATP. In addition, T3 and T4 initiate the transcription of genes involved in glucose
oxidation. Although these mechanisms prompt cells to produce more ATP, the process is
inefficient, and an abnormally increased level of heat is released as a byproduct of these
reactions.
This so-called calorigenic effect raises body temperature. Adequate levels of
thyroid hormones are also required for protein synthesis and for fetal and childhood tissue
development and growth. They are especially critical for normal development of the
nervous system both in utero and in early childhood, and they continue to support
neurological function in adults. These thyroid hormones have a complex interrelationship
with reproductive hormones, and deficiencies can influence libido, fertility, and other
aspects of reproductive function. Finally, thyroid hormones increase the body’s sensitivity
to catecholamines (epinephrine and norepinephrine) from the adrenal medulla by
upregulation of receptors in the blood vessels. When levels of T3 and T4 hormones are
excessive, this effect accelerates the heart rate, strengthens the heartbeat, and
increases blood pressure.
Because thyroid hormones regulate metabolism, heat production, protein
synthesis, and many other body functions, thyroid disorders can have severe and
widespread consequences.
Iodine Deficiency, Hypothyroidism, and Hyperthyroidism
Dietary iodine deficiency can result in the impaired ability to synthesize T3 and T4,
leading to a variety of severe disorders. When T3 and T4 cannot be produced, TSH is
secreted in increasing amounts. As a result of this hyperstimulation, thyroglobulin
accumulates in the thyroid gland follicles, increasing their deposits of colloid.
1. Goiter – The accumulation of colloid increases the overall size of the thyroid
gland. It is only a visible indication of the deficiency.
2. Neonatal hypothyroidism (cretinism) - is characterized by cognitive deficits,
short stature, and sometimes deafness and muteness in children and adults
born to mothers who were iodine deficient during pregnancy.
3. Hypothyroidism - inflammation of the thyroid gland is the more common cause
of low blood levels of thyroid hormones. The condition is characterized by a
low metabolic rate, weight gain, cold extremities, constipation, reduced libido,
menstrual irregularities, and reduced mental activity.
4. Hyperthyroidism—an abnormally elevated blood level of thyroid hormones
which is often caused by a pituitary or thyroid tumor.
Mammary Gland
Each breast is a hemispheric projection of variable size anterior to the pectoralis
major and serratus anterior muscles and attached to them by a layer of fascia composed
of dense irregular connective tissue. Each breast has one pigmented projection, the
nipple, that has a series of closely spaced openings of ducts called lactiferous ducts,
where milk emerges. The circular pigmented area of skin surrounding the nipple is called
the areola; it appears rough because it contains modified sebaceous (oil) glands.
Strands of connective tissue called the suspensory ligaments of the breast (Cooper’s
ligaments) run between the skin and fascia and support the breast. These ligaments
become looser with age or with the excessive strain that can occur in long-term jogging
or high-impact aerobics. Wearing a supportive bra can slow this process and help
maintain the strength of the suspensory ligaments.
Within each breast is a mammary gland, a modified sudoriferous (sweat) gland
that produces milk. A mammary gland consists of 15 to 20 lobes, or compartments,
separated by a variable amount of adipose tissue. In each lobe are several smaller
compartments called lobules, composed of grapelike clusters of milk-secreting glands
termed alveoli embedded in connective tissue. Contraction of myoepithelial cells
surrounding the alveoli helps propel milk toward the nipples. When milk is being
produced, it passes from the alveoli into a series of secondary tubules and then into the
mammary ducts. Near the nipple, the mammary ducts expand slightly to form sinuses
called lactiferous sinuses, where some milk may be stored before draining into a
lactiferous duct. Each lactiferous duct typically carries milk from one of the lobes to the
exterior.
Function of Mammary Gland
The functions of the mammary glands are the synthesis, secretion, and ejection
of milk; these functions, called lactation, are associated with pregnancy and childbirth.
Milk production is stimulated largely by the hormone prolactin from the anterior
pituitary, with contributions from progesterone and estrogens. The ejection of milk is
stimulated by oxytocin, which is released from the posterior pituitary in response to the
sucking of an infant on the mother’s nipple (suckling).