The
Skeletal System
Function of Bones
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Support – form the framework that supports the body
and cradles soft organs
Protection – provide a protective case for the brain,
spinal cord, and vital organs
Movement – provide levers for muscles
Mineral storage – reservoir for minerals, especially
calcium and phosphorus
Blood cell formation – hematopoiesis occurs within
the marrow cavities of bones
Bone Markings
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Bulges, depressions, and holes that serve
as:
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Sites of attachment for muscles, ligaments, and
tendons
Joint surfaces
Conduits for blood vessels and nerves
Bone Markings: Projections –
Sites of Muscle and Ligament Attachment
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Tuberosity – rounded projection
Crest – narrow, prominent ridge of bone
Trochanter – large, blunt, irregular surface
Line – narrow ridge of bone
Bone Markings: Projections –
Sites of Muscle and Ligament Attachment
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Tubercle – small rounded projection
Epicondyle – raised area above a condyle
Spine – sharp, slender projection
Process – any bony prominence
Bone Markings: Projections –
Projections That Help to Form Joints
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Head – bony expansion carried on a narrow
neck
Facet – smooth, nearly flat articular surface
Condyle – rounded articular projection
Ramus – armlike bar of bone
Bone Markings: Depressions and
Openings
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Meatus – canal-like passageway
Sinus – cavity within a bone
Fossa – shallow, basinlike depression
Groove – furrow
Fissure – narrow, slitlike opening
Foramen – round or oval opening through a
bone
The Skeletal and Muscular Systems
Video
There are 206 bones in the human
body
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A. The axial skeleton includes the skull and
the vertebral column.
Frontal View of the Skull
The Skull
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The skull, the body’s most complex bony structure, is
formed by the cranium and facial bones
Cranium – protects the brain and is the site of
attachment for head and neck muscles
Facial bones
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Supply the framework of the face, the sense organs, and
the teeth
Provide openings for the passage of air and food
Anchor the facial muscles of expression
Anatomy of the Cranium
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Eight cranial bones –
two parietal, two
temporal, frontal,
occipital, sphenoid, and
ethmoid
Cranial bones are thin
and remarkably strong
for their weight
Skull: Posterior View
Parietal Bones and Major Associated Sutures
Form most of the superior and lateral aspects of the skull
Superior View of the Skull
Posterior View of the Skull
1.
Occipital Bone
2.
Lambdoidal Suture
3.
Parietal Bone
4.
Sagittal Suture
5.
Coronal Suture
6.
Frontal Bone
Lateral View of the Skull
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1.Parietal Bone
2. Coronal Suture
3. Frontal Bone
4. Nasal Bone
5.Vomer
6. Lacrimal Bone
7. Orbital Part of Ethmoid
8. Zygomatic Bone
9. Maxilla
10. Body of Mandible
11. Ramus of Mandible
12.Coronoid Process
13.Mandibular Condyle
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14.Mental Foramen
15.Styloid Process
16. External Acoustic Meatus
17. Mastoid Process
18. Zygomatic Process
19.Temporal Bone
20. Greater Wing of Sphenoid
21.Inferior Temporal Line
22. Superior Temporal Line
23.Squamosal Suture
24.Lambdoidal Suture
25.Occipital Bone
Bones of the Skull
Inferior of the Cranial Vault
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The bone at the top is the Frontal Bone. The tongue
shaped bone below the Frontal Bone is the Ethmoid
Bone. Below that is the Sphenoid Bone. To the left
and the right in below the Sphenoid Bone are the
Left and Right Temporal Bones. In the Occiput at
the bottom of the picture you will notice a large
opening, called the Foramen Magnum, through
which the spinal cord passes. (Photo by Paula
Kliewer Photography)
Inferior View of the Skull
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1.Anterior Palatine Foramen
2. Palatine Process of Maxilla
3. Palatine
4. Greater Palatine Foramen
5.Lesser Palatine Foramen
6. Pterygoid Processes of Sphenoid
7.Zygomatic Process
8. Squamous Part of Temporal Bone
9. Mandibular Fossa
10. Styloid Process
11.Stylomastoid Foramen
12. Mastoid Process
13.Mastoid Foramen
14. Superior Nuchal Line
15. External Occipital Protruberance
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16.Median Nuchal Line
17. Inferior Nuchal Line1
8.Foramen Magnum
19. Condyloid Canal
20.Occipital Condyle
21.Hypoglossal Canal
22.Jugular Foramen
23.Carotid Canal
24.Foramen Spinosum
25.Foramen Ovale
26.Foramen Lacerum
27.Vomer
28.Transverse Palatine Suture
29.Median Palatine Suture
Hyoid
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1. Greater horns
2.Lesser horns
3. Body
Temporal Bones
Sphenoid Bone
Ethmoid Bone
Wormian Bones
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Tiny irregularly shaped bones that appear
within sutures
Mandible and Its Markings
Maxillary Bone
Orbits
Nasal Cavity
Nasal Cavity
Paranasal Sinuses
Vertebral Column
Vertebral Column
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Formed from 26 irregular
bones (vertebrae) connected
in such a way that a flexible
curved structure results
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Cervical vertebrae – 7
bones of the neck
Thoracic vertebrae – 12
bones of the torso
Lumbar vertebrae – 5
bones of the lower back
Sacrum – bone inferior to
the lumbar vertebrae that
articulates with the hip
bones
Vertebral Column: Curvatures
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Posteriorly concave curvatures – cervical
and lumbar
Posteriorly convex curvatures – thoracic and
sacral
Abnormal spine curvatures include scoliosis
(abnormal lateral curve), kyphosis
(hunchback), and lordosis (swayback)
Vertebral Column: Ligaments
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Anterior and posterior
longitudinal ligaments –
continuous bands down
the front and back of
the spine from the neck
to the sacrum
Short ligaments
connect adjoining
vertebrae together
Vertebral Column: Intervertebral Discs
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Cushionlike pad
composed of two parts
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Nucleus pulposus –
inner gelatinous nucleus
that gives the disc its
elasticity and
compressibility
Annulus fibrosus –
surrounds the nucleus
pulposus with a collar
composed of collagen
and fibrocartilage
General Structure of Vertebrae
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Body or centrum – disc-shaped, weightbearing region
Vertebral arch – composed of pedicles and
laminae that, along with the centrum, enclose
the vertebral foramen
Vertebral foramina – make up the vertebral
canal through which the spinal cord passes
General Structure of Vertebrae
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Spinous processes project
posteriorly, and transverse
processes project laterally
Superior and inferior
articular processes –
protrude superiorly and
inferiorly from the pediclelamina junctions
Intervertebral foramina –
lateral openings formed from
notched areas on the
superior and inferior borders
of adjacent pedicles
Cervical Vertebrae
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Seven vertebrae (C1-C7) are
the smallest, lightest
vertebrae
C3-C7 are distinguished with
an oval body, short spinous
processes, and large,
triangular vertebral foramina
Each transverse process
contains a transverse
foramen
Cervical Vertebrae: The Atlas (C1)
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The atlas has no body
and no spinous process
It consists of anterior
and posterior arches,
and two lateral masses
The superior surfaces
of lateral masses
articulate with the
occipital condyles
Cervical Vertebrae: The Axis (C2)
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The axis has a body, spine,
and vertebral arches as do
other cervical vertebrae
Unique to the axis is the
dens, or odontoid process,
which projects superiorly
from the body and is cradled
in the anterior arch of the
atlas
The dens is a pivot for the
rotation of the atlas
Cervical Vertebrae: The Atlas (C2)
Thoracic Vertebrae
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There are twelve vertebrae (T1T12) all of which articulate with
ribs
Major markings include two
facets and two demifacets on
the heart-shaped body, the
circular vertebral foramen,
transverse processes, and a
long spinous process
The location of the articulate
facets prevents flexion and
extension, but allows rotation of
this area of the spine
Lumbar Vertebrae
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The five lumbar vertebrae
(L1-L5) are located in the
small of the back and have
an enhanced weight-bearing
function
They have short, thick
pedicles and laminae, flat
hatchet-shaped spinous
processes, and a triangularshaped vertebral foramen
Orientation of articular facets
locks the lumbar vertebrae
together to provide stability
Sacrum
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Sacrum
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Consists of five fused vertebrae (S1-S5), which
shape the posterior wall of the pelvis
It articulates with L5 superiorly, and with the
auricular surfaces of the hip bones
Major markings include the sacral promontory,
transverse lines, alae, dorsal sacral foramina,
sacral canal, and sacral hiatus
Coccyx
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Coccyx (Tailbone)
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The coccyx is made up
of four (in some cases
three to five) fused
vertebrae that articulate
superiorly with the
sacrum
Bony Thorax (Thoracic Cage)
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The thoracic cage is composed of
the thoracic vertebrae dorsally, the
ribs laterally, and the sternum and
costal cartilages anteriorly
Functions
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Forms a protective cage around the
heart, lungs, and great blood
vessels
Supports the shoulder girdles and
upper limbs
Provides attachment for many neck,
back, chest, and shoulder muscles
Uses intercostal muscles to lift and
depress the thorax during breathing
Thoracic Cage
Bony Thorax (Thoracic Cage)
Sternum (Breastbone)
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A dagger-shaped, flat bone that lies in the
anterior midline of the thorax
Results from the fusion of three bones – the
superior manubrium, the body, and the
inferior xiphoid process
Anatomical landmarks include the jugular
(suprasternal) notch, the sternal angle, and
the xiphisternal joint
Ribs
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There are twelve pair of ribs
forming the flaring sides of the
thoracic cage
All ribs attach posteriorly to the
thoracic vertebrae
The superior 7 pair (true, or
vertebrosternal ribs) attach directly
to the sternum via costal cartilages
Ribs 8-10 (false, or vertebrocondral
ribs) attach indirectly to the sternum
via costal cartilage
Ribs 11-12 (floating, or vertebral
ribs) have no anterior attachment
Structure of a Typical True Rib
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Bowed, flat bone
consisting of a head,
neck, tubercle, and
shaft
Appendicular Skeleton
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The appendicular skeleton is made up of the
bones of the limbs and their girdles
Pectoral girdles attach the upper limbs to the
body trunk
Pelvic girdle secures the lower limbs
Pectoral Girdles (Shoulder Girdles)
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The pectoral girdles consist
of the anterior clavicles and
the posterior scapulae
They attach the upper limbs
to the axial skeleton in a
manner that allows for
maximum movement
They provide attachment
points for muscles that move
the upper limbs
Clavicles (Collarbones)
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The clavicles are slender,
doubly curved long bones
lying across the superior
thorax
The acromial (lateral) end
articulates with the scapula,
and the sternal (medial) end
articulates with the sternum
They provide attachment
points for numerous
muscles, and act as braces
to hold the scapulae and
arms out laterally away from
the body
Scapulae (Shoulder Blades)
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The scapulae are triangular,
flat bones lying on the dorsal
surface of the rib cage,
between the second and
seventh ribs
Scapulae have three
borders and three angles
Major markings include the
suprascapular notch, the
supraspinous and
infraspinous fossae, the
spine, the acromion, and the
coracoid process
The Upper Limb
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The upper limb consists of the arm
(brachium), forearm (antebrachium), and
hand (manus)
Thirty-seven bones form the skeletal
framework of each upper limb
Arm
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The humerus is the
sole bone of the arm
It articulates with the
scapula at the shoulder,
and the radius and ulna
at the elbow
Forearm
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The bones of the forearm
are the radius and ulna
They articulate proximally
with the humerus and
distally with the wrist bones
They also articulate with
each other proximally and
distally at small radioulnar
joints
Interosseous membrane
connects the two bones
along their entire length
Hand
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Skeleton of the hand
contains wrist bones
(carpals), bones of the
palm (metacarpals),
and bones of the
fingers (phalanges)
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Carpus (Wrist)
Consists of eight bones
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Scaphoid, lunate,
triquetral, and pisiform
proximally
Trapezium, trapezoid,
capitate, and hamate
distally
Metacarpus (Palm)
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Five numbered (1-5) metacarpal bones
radiate from the wrist to form the palm
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Their bases articulate with the carpals proximally,
and with each other medially and laterally
Heads articulate with the phalanges
Phalanges (Fingers)
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Each hand contains 14
miniature long bones called
phalanges
Fingers (digits) are
numbered 1-5, beginning
with the thumb (pollex)
Each finger (except the
thumb) has three phalanges
– distal, middle, and
proximal
The thumb has no middle
phalanx
Pelvic Girdle (Hip)
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The hip is formed by a pair of
hip bones (os coxae, or coxal)
Together with the sacrum and
the coccyx, these bones form
the bony pelvis
The pelvis
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Attaches the lower limbs to the
axial skeleton with the
strongest ligaments of the body
Transmits weight of the upper
body to the lower limbs
Supports the visceral organs of
the pelvis
Ilium
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The ilium is a large flaring bone that
forms the superior region of the
coxal bone
It consists of a body and a superior
winglike portion called the ala
The broad posterolateral surface is
called the gluteal surface
The auricular surface articulates
with the sacrum (sacroiliac joint)
Major markings include the iliac
crests, four spines, greater sciatic
notch, iliac fossa, arcuate line, and
the pelvic brim
Ilium: Medial View
Ischium
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The ischium forms the
posteroinferior part of the hip
bone
The thick body articulates
with the ilium, and the
thinner ramus articulates
with the pubis
Major markings include the
ischial spine, lesser sciatic
notch, and the ischial
tuberosity
Pubis
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The pubic bone forms the
anterior portion of the hip
bone
It articulates with the ischium
and the ilium
Major markings include
superior and inferior rami,
the pubic crest, pubic
tubercle, pubic arch, pubic
symphysis, and obturator
foramen (along with ilium
and ischium)
Pubis: Medial View
Comparison of Male and Female Pelvic
Structure
Comparison of Male and Female Pelvic
Structure
Characteristic
Female
Male
Bone thickness
Lighter, thinner, and
smoother
Heavier, thicker, and
more prominent
markings
Pubic
arch/angle
80˚–90˚
50˚–60˚
Acetabula
Small; farther apart
Large; closer
together
Sacrum
Wider, shorter; sacral
curvature is accentuated
Narrow, longer;
sacral promontory
more ventral
Coccyx
More movable; straighter
Less movable;
curves ventrally
The Lower Limb
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The three segments of the lower limb are the
thigh, leg, and foot
They carry the weight of the erect body, and
are subjected to exceptional forces when one
jumps or runs
Femur
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The sole bone of the thigh is
the femur, the largest and
strongest bone in the body
It articulates proximally with
the hip and distally with the
tibia and fibula
Major markings include the
head, fovea capitis, greater
and lesser trochanters,
gluteal tuberosity, lateral and
medial condyles and
epicondyles, linea aspera,
patellar surface, and the
intercondylar notch
Leg
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The tibia and fibula form the skeleton of the
leg
They are connected to each other by the
interosseous membrane
They articulate with the femur proximally and
with the ankle bones distally
They also articulate with each other via the
immovable tibiofibular joints
Tibia
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Receives the weight of the
body from the femur and
transmits it to the foot
Major markings include
medial and lateral condyles,
intercondylar eminence, the
tibial tuberosity, anterior
crest, medial malleolus, and
fibular notch
Fibula
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Sticklike bone with slightly expanded ends
located laterally to the tibia
Major markings include the head and lateral
malleolus
Foot
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The skeleton of the foot
includes the tarsus,
metatarsus, and the
phalanges (toes)
The foot supports body
weight and acts as a
lever to propel the body
forward in walking and
running
Tarsus
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Composed of seven bones
that form the posterior half of
the foot
Body weight is carried
primarily on the talus and
calcaneus
Talus articulates with the
tibia and fibula superiorly,
and the calcaneus inferiorly
Other tarsus bones include
the cuboid and navicular,
and the medial,
intermediate, and lateral
cuneiforms
Calcaneus
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Forms the heel of the foot
Carries the talus on its superior surface
Point of attachment for the calcaneal
(Achilles) tendon of the calf muscles
Metatarsus and Phalanges
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Metatarsus and Phalanges
Metatarsals
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Five (1-5) long bones that
articulate with the proximal
phalanges
The enlarged head of
metatarsal 1 forms the “ball
of the foot”
Phalanges
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The 14 bones of the toes
Each digit has three
phalanges except the
hallux, which has no middle
phalanx
Arches of the Foot
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The foot has three arches
maintained by interlocking foot
bones and strong ligaments
Arches allow the foot to hold up
weight
The arches are:
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Lateral longitudinal – cuboid is
keystone of this arch
Medial longitudinal – talus is
keystone of this arch
Transverse – runs obliquely
from one side of the foot to the
other
Developmental Aspects: Fetal Skull
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Infant skull has more bones
than the adult skull
At birth, fetal skull bones are
incomplete and connected
by fontanels
Fontanels
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Unossified remnants of
fibrous membranes
between fetal skull bones
The four fontanels are
anterior, posterior, mastoid,
and sphenoid
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B. The appendicular skeleton includes the
bones of the arms and legs and structures
associated with them (shoulder, hip, wrist,
ankle, fingers, toes).
Upper Limb
Lower Limb
Classification of Bones: By Shape
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Long bones – longer than
they are wide
(e.g., humerus)
Classification of Bones: By Shape
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Short bones
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Cube-shaped bones of
the wrist and ankle
Bones that form within
tendons (e.g., patella)
Classification of Bones: By Shape
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Flat bones –
thin, flattened,
and a bit curved
(e.g., sternum,
and most skull
bones)
Classification of Bones: By Shape
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Irregular bones –
bones with
complicated shapes
(e.g., vertebrae and
hip bones)
Shapes of Bones Video
Joints Chapter 8
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C. Joints are where two or more bones
meet.
Joints (Articulations)
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Weakest parts of the skeleton
Articulation – site where two or more bones
meet
Functions of joints
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Give the skeleton mobility
Hold the skeleton together
Classification of Joints: Structural
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Structural classification focuses on the
material binding bones together and whether
or not a joint cavity is present
The three structural classifications are:
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Fibrous
Cartilaginous
Synovial
Classification of Joints: Functional
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Functional classification is based on the
amount of movement allowed by the joint
The three functional classes of joints are:
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Synarthroses – immovable
Amphiarthroses – slightly movable
Diarthroses – freely movable
Fibrous Structural Joints
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The bones are joined by fibrous tissues
There is no joint cavity
Most are immovable
There are three types – sutures,
syndesmoses, and gomphoses
Fibrous Structural Joints: Sutures
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Occur between the bones of the skull
Comprised of interlocking junctions
completely filled with connective tissue fibers
Bind bones tightly together, but allow for
growth during youth
In middle age, skull bones fuse and are
called synostoses
Fibrous Structural Joints: Sutures
Fibrous Structural Joints:
Syndesmoses
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Bones are connected by a
fibrous tissue ligament
Movement varies from
immovable to slightly
variable
Examples include the
connection between the tibia
and fibula, and the radius
and ulna
Fibrous Structural Joints: Gomphoses
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The peg-in-socket fibrous joint between a
tooth and its alveolar socket
The fibrous connection is the periodontal
ligament
Cartilaginous Joints
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Articulating bones are united by cartilage
Lack a joint cavity
Two types – synchondroses and symphyses
Cartilaginous Joints: Synchondroses
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A bar or plate of hyaline
cartilage unites the
bones
All synchondroses are
synarthrotic
Examples include:
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Epiphyseal plates of
children
Joint between the costal
cartilage of the first rib
and the sternum
Cartilaginous Joints: Symphyses
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Hyaline cartilage covers the
articulating surface of the
bone and is fused to an
intervening pad of
fibrocartilage
Amphiarthrotic joints
designed for strength and
flexibility
Examples include
intervertebral joints and the
pubic symphysis of the
pelvis
Synovial Joints
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Those joints in which the articulating bones
are separated by a fluid-containing joint
cavity
All are freely movable diarthroses
Examples – all limb joints, and most joints of
the body
Synovial Joints: General Structure
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Synovial joints all have
the following
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Articular cartilage
Joint (synovial) cavity
Articular capsule
Synovial fluid
Reinforcing ligaments
Synovial Joints: Friction-Reducing
Structures
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Bursae – flattened, fibrous
sacs lined with synovial
membranes and containing
synovial fluid
Common where ligaments,
muscles, skin, tendons, or
bones rub together
Tendon sheath – elongated
bursa that wraps completely
around a tendon
Synovial Joints: Movement
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The two muscle attachments across a joint
are:
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Origin – attachment to the immovable bone
Insertion – attachment to the movable bone
Described as movement along transverse,
frontal, or sagittal planes
Synovial Joints: Range of Motion
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Nonaxial – slipping movements only
Uniaxial – movement in one plane
Biaxial – movement in two planes
Multiaxial – movement in or around all three
planes
Gliding Movements
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One flat bone surface glides or slips over
another similar surface
Examples – intercarpal and intertarsal joints,
and between the flat articular processes of
the vertebrae
Angular Movement
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Flexion — bending movement that decreases the angle of the
joint
Extension — reverse of flexion; joint angle is increased
Dorsiflexion and plantar flexion — up and down movement of
the foot
Abduction — movement away from the midline
Adduction — movement toward the midline
Circumduction — movement describes a cone in space
Gliding Movement
Angular Movement: Flexion/Extension
Hypertension/Flexion
Dorsiflexion/Plantar flexion
Abduction/Adduction/Circumduction
Rotation



Rotation
The turning of a bone
around its own long
axis
Examples
–
–
Between first two
vertebrae
Hip and shoulder joints
Special Movements





Supination and pronation
Inversion and eversion
Protraction and retraction
Elevation and depression
Opposition
Supination/Pronation
Inversion/Eversion
Protraction/Retraction
Elevation/Depression
Opposition
Joints Video
Hinge Joint:

Hinge joints
–
–
–
–
Cylindrical projections of
one bone fits into a troughshaped surface on another
Motion is along a single
plane
Uniaxial joints permit flexion
and extension only
Examples: elbow and
interphalangeal joints
Condyloid, or Ellipsoidal, Joints




Oval articular surface of one
bone fits into a
complementary depression
in another
Both articular surfaces are
oval
Biaxial joints permit all
angular motions
Examples: radiocarpal
(wrist) joints, and
metacarpophalangeal
(knuckle) joints
Saddle Joint





Condyloid, or Ellipsoidal, Joints
Oval articular surface of one
bone fits into a complementary
depression in another
Both articular surfaces are oval
Biaxial joints permit all angular
motions
Examples: radiocarpal (wrist)
joints, and
metacarpophalangeal (knuckle)
joints
Ball and Socket Joint



A spherical or
hemispherical head of
one bone articulates
with a cuplike socket of
another
Multiaxial joints permit
the most freely moving
synovial joints
Examples: shoulder
and hip joints
Gliding Joint
Pivot Joint



Rounded end of
one bone protrudes
into a “sleeve,” or
ring, composed of
bone (and possibly
ligaments) of
another
Only uniaxial
movement allowed
Examples: joint
between the axis
and the dens, and
the proximal
radioulnar joint
Synovial Joints: Knee



Largest and most complex
joint of the body
Allows flexion, extension,
and some rotation
Three joints in one
surrounded by a single joint
cavity
–
–
Femoropatellar
Lateral and medial
tibiofemoral joints
Synovial Joints: Knee –
Other Supporting Structures




Anterior cruciate
ligament
Posterior cruciate
ligament
Medial meniscus
(semilunar cartilage)
Lateral meniscus
Synovial Joints: Knee –
Posterior Superficial View





Adductor magnus
tendon
Articular capsule
Oblique popliteal
ligament
Arcuate popliteal
ligament
Semimembranosus
tendon
Synovial Joints: Shoulder Stability
Hip
Elbow
Bones and Cartilage Video
Ligaments

D. Ligaments are tough bands of connective
tissue that attaches one bone to another.
Tendons

E. Bands of cartilage that binds muscle to
bone.
Bursae

E. Bursae act to decrease friction and keep
bones and tendons from rubbing against
each other.
Structure of Bone

F. Anatomy of a bone:
–
1. Compact bone

a. Found in the middle of long bones
Structure of Long Bone


Long bones consist of a diaphysis and an
epiphysis
Diaphysis
–
–
–
Tubular shaft that forms the axis of long bones
Composed of compact bone that surrounds the
medullary cavity
Yellow bone marrow (fat) is contained in the
medullary cavity

The medullary cavity is
the space within the
diaphysis.
Structure of Long Bone

Epiphyses
–
–
–
–
Expanded ends of long bones
Exterior is compact bone, and the interior is
spongy bone
Joint surface is covered with articular (hyaline)
cartilage
Epiphyseal line separates the diaphysis from the
epiphyses
Structure of Long Bone
Bone Membranes

Periosteum – doublelayered protective
membrane
–
–
–
–

Outer fibrous layer is dense
regular connective tissue
Inner osteogenic layer is
composed of osteoblasts
and osteoclasts
Richly supplied with nerve
fibers, blood, and lymphatic
vessels, which enter the
bone via nutrient foramina
Secured to underlying bone
by Sharpey’s fibers
Endosteum – delicate
membrane covering internal
surfaces of bone
Structure of Short, Irregular, and Flat Bones



Thin plates of periosteum-covered compact
bone on the outside with endosteum-covered
spongy bone (diploë) on the inside
Have no diaphysis or epiphyses
Contain bone marrow between the
trabeculae
Structure of a Flat Bone
Location of Hematopoietic Tissue (Red Marrow)

In infants
–

Found in the medullary cavity and all areas of
spongy bone
In adults
–
Found in the diploë of flat bones, and the head of
the femur and humerus
Microscopic Structure of Bone:
Compact Bone

Haversian system, or osteon – the structural unit of
compact bone
–
–
–
Lamella – weight-bearing, column-like matrix tubes
composed mainly of collagen
Haversian, or central canal – central channel containing
blood vessels and nerves
Volkmann’s canals – channels lying at right angles to the
central canal, connecting blood and nerve supply of the
periosteum to that of the Haversian canal
Microscopic Bone
Microscopic Structure of Bone: Compact Bone



Osteocytes – mature bone cells
Lacunae – small cavities in bone that contain
osteocytes
Canaliculi – hairlike canals that connect
lacunae to each other and the central canal
Microscopic Structure of Bone: Compact Bone
–
2. Spongy bone

a. Found at the ends of long bone
Cartilage Video
Chemical Composition of Bone: Organic




Osteoblasts – bone-forming cells
Osteocytes – mature bone cells
Osteoclasts – large cells that resorb or break
down bone matrix
Osteoid – unmineralized bone matrix
composed of proteoglycans, glycoproteins,
and collagen
Chemical Composition of Bone:
Inorganic

Hydroxyapatites, or mineral salts
–
–
–
Sixty-five percent of bone by mass
Mainly calcium phosphates
Responsible for bone hardness and its resistance
to compression
–
4. Your bones grow in length and diameter.

a. Growth occurs are growth plate
Bone Development

Osteogenesis and ossification – the process
of bone tissue formation, which leads to:
–
–
–
The formation of the bony skeleton in embryos
Bone growth until early adulthood
Bone thickness, remodeling, and repair
How Bones Change Video
Formation of the Bony Skeleton



Begins at week 8 of embryo development
Intramembranous ossification – bone
develops from a fibrous membrane
Endochondral ossification – bone forms by
replacing hyaline cartilage
Intramembranous Ossification


Formation of most of the flat bones of the
skull and the clavicles
Fibrous connective tissue membranes are
formed by mesenchymal cells
Stages of Intramembranous
Ossification




An ossification center appears in the fibrous
connective tissue membrane
Bone matrix is secreted within the fibrous
membrane
Woven bone and periosteum form
Bone collar of compact bone forms, and red
marrow appears
Stages of Intramembranous Ossification
Stages of Intramembranous Ossification
Stages of Intramembranous Ossification
Stages of Intramembranous Ossification
Endochondral Ossification



Begins in the second month of development
Uses hyaline cartilage “bones” as models for
bone construction
Requires breakdown of hyaline cartilage prior
to ossification
Stages of Endochondral Ossification
Long Bone Growth and Remodeling
Appositional Growth of Bone
Importance of Ionic Calcium in the
Body

Calcium is necessary for:
–
–
–
–
–
Transmission of nerve impulses
Muscle contraction
Blood coagulation
Secretion by glands and nerve cells
Cell division
Hormonal Mechanism




Rising blood Ca2+ levels trigger the thyroid to release
calcitonin
Calcitonin stimulates calcium salt deposit in bone
Falling blood Ca2+ levels signal the parathyroid
glands to release PTH
PTH signals osteoclasts to degrade bone matrix and
release Ca2+ into the blood
Hormonal Mechanism
Importance of Ionic Calcium in the
Body

Calcium is necessary for:
–
–
–
–
–
Transmission of nerve impulses
Muscle contraction
Blood coagulation
Secretion by glands and nerve cells
Cell division
Response to Mechanical Stress


Wolff’s law – a bone grows or remodels in
response to the forces or demands placed
upon it
Observations supporting Wolff’s law include
–
–
Long bones are thickest midway along the shaft
(where bending stress is greatest)
Curved bones are thickest where they are most
likely to buckle
Bone Fractures (Breaks)

Bone fractures are classified by:
–
–
–
–
The position of the bone ends after fracture
The completeness of the break
The orientation of the bone to the long axis
Whether or not the bones ends penetrate the skin
Types of Bone Fractures





Nondisplaced – bone ends retain their normal
position
Displaced – bone ends are out of normal alignment
Complete – bone is broken all the way through
Incomplete – bone is not broken all the way through
Linear – the fracture is parallel to the long axis of the
bone
Types of Bone Fractures



Transverse – the fracture is perpendicular to
the long axis of the bone
Compound (open) – bone ends penetrate the
skin
Simple (closed) – bone ends do not
penetrate the skin
Common Types of Fractures




Comminuted – bone fragments into three or more
pieces; common in the elderly
Spiral – ragged break when bone is excessively
twisted; common sports injury
Depressed – broken bone portion pressed inward;
typical skull fracture
Compression – bone is crushed; common in porous
bones
Common Types of Fractures


Epiphyseal – epiphysis separates from
diaphysis along epiphyseal line; occurs
where cartilage cells are dying
Greenstick – incomplete fracture where one
side of the bone breaks and the other side
bends; common in children
Stages in the Healing of a Bone Fracture
Hematoma formation
Torn blood vessels hemorrhage
A mass of clotted blood (hematoma)
forms at the fracture site
Site becomes swollen, painful, and
inflamed
Stages in the Healing of a Bone Fracture
Fibrocartilaginous callus forms
Granulation tissue (soft callus) forms a few
days after the fracture
Capillaries grow into the tissue and
phagocytic cells begin cleaning debris
Bones produce blood cells in the red marrow.
–
a. Found in






1.
2.
3.
4.
5.
6.
humerus
femur
sternum
ribs
vertebrae
pelvis
Stages in the Healing of a Bone Fracture
The fibrocartilaginous callus forms when:
–
–
–
–
Osteoblasts and fibroblasts migrate to the fracture
and begin reconstructing the bone
Fibroblasts secrete collagen fibers that connect
broken bone ends
Osteoblasts begin forming spongy bone
Osteoblasts furthest from capillaries secrete an
externally bulging cartilaginous matrix that later
calcifies
Stages in the Healing of a Bone Fracture
Bony callus formation
New bone trabeculae appear in the
fibrocartilaginous callus
Fibrocartilaginous callus converts into
a bony (hard) callus
Bone callus begins 3-4 weeks after
injury, and continues until firm union is
formed 2-3 months later
Stages in the Healing of a Bone Fracture
Stages in the Healing of a Bone
Fracture
Bone remodeling
Excess material on the bone shaft
exterior and in the medullary canal is
removed
Compact bone is laid down to
reconstruct shaft walls
Homeostatic Imbalances

Osteomalacia
–
–
–
Bones are inadequately mineralized causing
softened, weakened bones
Main symptom is pain when weight is put on the
affected bone
Caused by insufficient calcium in the diet, or by
vitamin D deficiency
Homeostatic Imbalances

Rickets
–
–
–
Bones of children are inadequately mineralized
causing softened, weakened bones
Bowed legs and deformities of the pelvis, skull,
and rib cage are common
Caused by insufficient calcium in the diet, or by
vitamin D deficiency
Homeostatic Imbalances

Osteoporosis
–
–
–
–
Group of diseases in which bone reabsorption
outpaces bone deposit
Spongy bone of the spine is most vulnerable
Occurs most often in postmenopausal women
Bones become so fragile that sneezing or
stepping off a curb can cause fractures
Osteoporosis: Treatment





Calcium and vitamin D supplements
Increased weight-bearing exercise
Hormone (estrogen) replacement therapy
(HRT) slows bone loss
Natural progesterone cream prompts new
bone growth
Statins increase bone mineral density
Paget’s Disease




Characterized by excessive bone formation and
breakdown
Pagetic bone with an excessively high ratio of woven
to compact bone is formed
Pagetic bone, along with reduced mineralization,
causes spotty weakening of bone
Osteoclast activity wanes, but osteoblast activity
continues to work
Paget’s Disease



Usually localized in the spine, pelvis, femur,
and skull
Unknown cause (possibly viral)
Treatment includes the drugs Didronate and
Fosamax
Developmental Aspects of Bones



Mesoderm gives rise to embryonic
mesenchymal cells, which produce
membranes and cartilages that form the
embryonic skeleton
The embryonic skeleton ossifies in a
predictable timetable that allows fetal age to
be easily determined from sonograms
At birth, most long bones are well ossified
(except for their epiphyses)
Developmental Aspects of Bones



By age 25, nearly all bones are completely
ossified
In old age, bone reabsorption predominates
A single gene that codes for vitamin D
docking determines both the tendency to
accumulate bone mass early in life, and the
risk for osteoporosis later in life
–
6. Yellow bone marrow contains fat and is found
in many bones.
–
7. Bones store minerals.

a. Calcium and phosphate needed to form strong
bones.
–
1. Found in:
 Milk
 Yogurt
 Cheese
 Lettuce
 Spinach
 Leafy vegetables
Care
–
8. Bones can become more brittle with age:
osteoporosis. Caused by loss of bone volume
and content.
Quiz