Essentials of Human Anatomy
Anatomy of the Muscular System
Dr Fadel Naim
Ass. Prof. Faculty of Medicine
IUG
Chapter 6
Introduction
• There are more than 600 skeletal
muscles in the body
• From 40% to 50% of body weight is
skeletal muscle
• Muscles, along with the skeleton,
determine the form and contour of the
body
Functions of skeletal Muscles
• Body movements
• Maintaining Posture
• Stabilizing Joints
• Body positions
• Generating heat
4 Unique Characteristics of Muscle Tissue
• Excitability is equated with responsiveness.
• Contractility causes the fiber to shorten
resulting in either a pull on bones or the
movement of specific body parts.
• Elasticity is the muscle’s ability to return to its
original length when tension is released.
• Extensibility is capability of extending in length
in response to the contraction of opposing
muscle fibers.
Structure of a Skeletal Muscle
Skeletal Muscle
• organ of the muscular
system
- skeletal muscle tissue
- nervous tissue
- blood
- connective tissues
• fascia
• tendons
• aponeuroses
Skeletal Muscle Tissue
• Skeletal muscles are organs
• Vary in shape and size
• A skeletal muscle is composed of cells
– Each cell is as long as the muscle
– Small muscle: 100 micrometers long; 10 micrometers
in diameter
– Large muscle: 35 centimeters long; 100 micrometers
in diameter
Skeletal Muscle Structure
• Connective tissue components
– Endomysium—delicate connective tissue
membrane that covers specialized skeletal
muscle fibers
– Perimysium—tough connective tissue
binding together fascicles
– Epimysium—coarse sheath covering the
muscle as a whole
– These three fibrous components may become
a tendon or an aponeurosis
Skeletal Muscle Anatomy
Muscle Fiber Structure
•
•
•
•
•
Multiple nuclei
Sarcolemma
T-tubules
Sarcoplasmic reticulum
Sarcoplasm
– Mitochondria
– Glycogen & ions
– Myofibrils
Muscle Fiber Structure
Skeletal Muscle Has Striations
• Appearance is due to size and density differences
between thick filaments and thin filaments.
• Under the light microscope, two differently shaded
bands are present.
• The dark bands, called A bands, contain the entire thick
filament.
• At either end of a thick filament is a region where thin
filaments extend into the A band between the stacked
thick filaments.
• Light bands, called I bands, contain thin filaments only.
• I band is lighter shaded than an A band because only
the thin filaments occupy this region.
Sarcomere: Organization of
Fibers
Z disks
I band
A band
H zone
M line
•
•
•
•
•
Neuromuscular Junction
• also known as
myoneural junction
• site where an axon and
muscle fiber meet
• motor neuron
• motor end plate
• synapse
• synaptic cleft
• synaptic vesicles
• neurotransmitters
Motor Unit
• single motor neuron
• all muscle fibers controlled by motor neuron
skeletal muscles Classification
• By the way fascicles are organized
• By relationships of fascicles to tendons
– 4 patterns of fascicle organization:
•
•
•
•
parallel
convergent
pennate
circular
Parallel Muscles
• Fibers parallel to the long axis
of muscle
• e.g., biceps brachii
• The center or body of the
muscle thickens when
parallel muscle contracts
• Parallel muscles contract
about 30%
Convergent Muscles
• A broad area converges on attachment
site (tendon, aponeurosis, or raphe)
• Muscle fibers pull in different directions,
depending on stimulation
• e.g., pectoralis muscles
Pennate Muscles
• Unipennate:
– fibers on 1 side of tendon e.g., extensor
digitorum
• Bipennate:
– fibers on both sides of tendon e.g., rectus
femoris
• Multipennate:
– tendon branches within muscle e.g., deltoid
Circular Muscles
• Also called sphincters
• Open and close to guard entrances of body
• e.g., obicularis oris
Types of Contractions
• isotonic – muscle contracts and
changes length
• eccentric – lengthening
contraction
• concentric – shortening contraction
• isometric – muscle contracts but
does not change length
Descriptive Names or Skeletal Muscles
1.
Location in the body-identifies body regions:
–
e.g., temporalis muscle
2.
Origin and insertion-First part of name indicates origin, second part of
name indicates insertion: e.g., genioglossus muscle
3.
Fascicle organization-Describes fascicle orientation within muscle: i.e.,
rectus (straight), transversus, oblique
4.
Relative position•
•
•
•
5.
Structural characteristics
•
•
•
6.
Externus (superficialis):visible at body surface
Internus (profundus):deep muscles
Extrinsic:muscles outside an organ
Intrinsic:muscles inside an organ
Action
Number of tendons: bi = 2, tri = 3
Shape: trapezius, deltoid, rhomboid
Size
Names for Muscle Size
•
•
•
•
•
Longus = long
Longissimus = longest
Teres = long and round
Brevis = short
Magnus = large
•
•
•
•
Major = larger
Maximus = largest
Minor = small
Minimus = smallest
• Action
– Movements:
• e.g., flexor, extensor, retractor
Muscle Atrophy
• Reduction in muscle size, tone, and
power.
• Due to reduced stimulation, it loses both
mass and tone.
• Muscle becomes flaccid, and its fibers
decrease in size and become weaker.
• Even a temporary reduction in muscle use
can lead to muscular atrophy.
Muscle Hypertrophy
• An increase in muscle fiber size.
• Muscle size may be improved by
exercising.
• Repetitive, exhaustive stimulation of
muscle fibers results in more mitochondria,
larger glycogen reserves, and an increased
ability to produce ATP.
• Ultimately, each muscle fiber develops
more myofibrils, and each myofibril
contains a larger number of myofilaments.
Three Types of Skeletal Muscle
Fibers
• Fast
– are large in diameter
– contain large glycogen reserves
– densely packed myofibrils
– relatively few mitochondria
– called white fibers due to lack of myoglobin
– majority of skeletal muscle fibers in the body
• Intermediate
– resemble fast fibers; however
– have a greater resistance to fatigue
• Slow
– smaller and they
– contract more slowly
– called red fibers because due to myoglobin
Posture
• Maintaining the posture of the body is one
of the major roles muscles play
• “Good posture”—body alignment that most
favors function and requires the least
muscular work to maintain, keeping the
body’s center of gravity over its base
Posture
• How posture is maintained
– Muscles exert a continual pull on bones in the
opposite direction from gravity
– Structures and systems other than muscle and
bones have a role in maintaining posture
• Nervous system—responsible for determining
muscle tone and also regulation and coordination of
the amount of pull exerted by individual muscles
• Respiratory, digestive, excretory, and endocrine
systems all contribute to maintain posture
Cycle of Life: Muscular System
• Life cycle changes—manifested in other
components of functional unit
– Infancy and childhood—coordination and controlling
of muscle contraction permits sequential development
steps
• Degenerative changes of advancing age result
in replacement of muscle cells with
nonfunctional connective tissue
– Diminished strength
Cycle of Life: Muscular System
• Muscle cells—increase or decrease in
number, size, and ability to shorten at
different periods
• Pathological conditions at different periods
may affect the muscular system
Axial Muscles
• Have both their origins and insertions on parts of
the axial skeleton.
• Support and move the head and spinal column.
• Function in nonverbal communication by affecting
facial features.
• Move the lower jaw during chewing.
• Assist in food processing and swallowing.
• Aid breathing.
• Support and protect the abdominal and pelvic
organs.
• Are not responsible for stabilizing or moving the
pectoral or pelvic girdles or their attached limbs.
Appendicular Muscles
• Control the movements of the upper and
lower limbs.
• Stabilize and control the movements of the
pectoral and pelvic girdles.
• Organized into groups based on their
location in the body or the part of the
skeleton they move.
• Work in groups that are either synergistic or
antagonistic.
Appendicular Muscles
• Organized into specific groups.
– muscles that move the pectoral girdle
– muscles that move the glenohumeral joint/arm
– arm and forearm muscles that move the elbow
joint/forearm
– forearm muscles that move the wrist joint, hand, and
fingers
– intrinsic muscles of the hand
Intramuscular Injections
• The gluteus maximus is a large,
thick muscle with coarse Fasciculi
that can be easily separated
without damage.
• The great thickness of this muscle
makes it ideal for intramuscular
Injections.
• To avoid injury to the underlying
Sciatic nerve, the injection should
be given well forward On the
upper outer quadrant of the
buttock.
MOVEMENT—FLEXSION
MOVEMENT—EXTENSION
MOVEMENT—EXTENSION
MOVEMENT
HYPEREXTENSION
MOVEMENT—DORSIFLEXION
PLANTAR FLEXION
MOVEMENT—ABDUCTION
ADDUCTION, CIRCUMDUCTION
MOVEMENT--ROTATION
MOVEMENT—SUPINATION
PRONATION
MOVEMENT—INVERSION
EVERSION
MOVEMENT—PROTRACTION
RETRACTION
THE END