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The Skeletal System. Organs – bones, joints, cartilage, ligaments. Functions. A. Support – hard framework that supports and anchors all soft organs of the body – Ex. Legs act as pillars to support trunk, rib cage supports thorax wall

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the skeletal system
The Skeletal System
  • Organs – bones, joints, cartilage, ligaments

A. Support – hard framework that supports and anchors all soft organs of the body – Ex. Legs act as pillars to support trunk, rib cage supports thorax wall

B. Protection – skull protects brain, ribs protect heart/lungs, zygomatic arch protect the eye

C. Movement – skeletal muscles, attached to bone by tendons, used the bones as levers to move the body and it’s parts; arrangement of bones and the design of joints determine the types of movement possible

functions con t
Functions (con’t)

D. Storage

  • Fat stored in the internal cavities
  • Bone matrix stores minerals (Ca+2) – “deposits” and “withdrawals” of minerals to and from bones goes on almost continuously

E. Blood cell formation (hemopoiesis)

  • Carried on in red bone marrow; hemopoietic tissue – Fig. 6-5
  • Hemopoietic tissue is found in the ends of long bones
  • Transformed to yellow bone marrow, an inactive fatty tissue, as person ages
classification of bones
Classification of Bones

A. Classified according to shape

B. Contain different proportions of

1. Compact bone (smooth & homogeneous)

2. Spongy (cancellous) bone – spaces & trabeculae (beams)

classification of bones1
Classification of Bones
  • Long bones

1. Longer than they

are wide

2. Consists of a shaft

plus two ends

3. Primarily compact

bone; but may

contain substantial

amounts of spongy


classification of bones2
Classification of Bones

D. Short bones

1. Roughly cube-like – ex. Wrist/ankle

2. Mostly spongy bone; compact bone only provides a

thin surface

classification of bones3
Classification of Bones

E. Flat Bone

1. Thin, flattened and usually a bit curved –

sternum, ribs, most skull bones

2. Two roughly parallel compact bone

surfaces with a layer of spongy bone


classification of bones4
Classification of Bones

F. Irregular bones – some skull, hip, vertebrae

1. Fit none of the preceding classes

2. Complex shapes

3. Mainly spongy bone enclosed by thin layers

of compact bone

G. Sesamoid bones –a special type of short bone

embedded within a tendon; ex. - patella

bone structure 2 levels
Bone Structure – 2 levels

A. Gross Anatomy – What you can see

with the naked eye - Fig. 6-1

B. Microscopic Anatomy – Fig. 6-2, 6.3

gross anatomy
Gross Anatomy

Long Bone – most have the same basic structure

1. diaphysis (shaft) – hollow tube of hard compact bone

2. medullary cavity – hollow area; contains yellow bone marrow

3. epiphyses – bone end or extremities; usually more expanded

than diaphysis; thin layer of compact bone forms exterior;

interior spongy bone filled with red bone marrow

4. epiphyseal line/plate – remnant of cartilage present at

junction of diaphysis & epiphyses in young bones; growth

are that allows bones to lengthen

5. articular cartilage – found where long bones articulate (join);

cushions the bone ends and absorbs stress during joint


6. periosteum – outer surface of diaphysis; richly supplied with

nerve fivbers, lymphatic vessels, and blood vessels which enter

via nutrient canals

7. endosteum – fibrous membrane that lines medullary cavity

microscopic anatomy
Microscopic Anatomy

Compact bone – Fig. 6-2, 6-3

1. Haversian system – structural unit; circular 7 tubelike;

composed of calcified matrix arranged in multiple layers (one inside the other – like an onion)

2. osteocytes (bone cells) – regulate the removal of calcium from

bone matrix

Osteocyte (within lacuna)

microscopic anatomy1
Microscopic Anatomy

Spongy bone

1. Trabeculae – structural unit

2. Osteocytes – only a few cell layers thick; no Haversian system

3. Nutrients reach osteocytes by diffusion

microscopic anatomy2
Microscopic Anatomy

Cartilage – Fig. 6-4

1. Fibers embedded in gel (not calcified matrix)

2. Chondrocytes (cartilage cells)

3. Cartilage contains no blood vessels; nutrients diffuse

through matrix

4. Function

a. supports & reinforces

b. cushioning properties

c. resists compressive stress (articular cartilage)

bone development osteogensis fig 6 5
Bone Development(osteogensis) – Fig. 6-5

A. Intramembranous ossification – flat bones form from fibrous membrane – ex. Skull, clavicle, ribs

B. Endochondral ossification – bone formation from hyaline cartilage structures; most bones form this way;

osteoblasts – bone forming cells

osteoclasts – bone reabsorbing cells

endochondral ossifcation fig
EndochondralOssifcation – Fig.

Cartilage model is the starting point

endochondral ossifcation fig1
EndochondralOssifcation – Fig.

Formation of a bone collar around the shaft of the hyaline cartilage model

endochondral ossifcation fig2
EndochondralOssifcation – Fig.

Cartilage matrix calcifies; chondrocytes die

endochondral ossifcation fig3
EndochondralOssifcation – Fig.

Invasion of internal cavities by periosteal bud and spongy bone formation (3 mo. embryo)

endochondral ossifcation fig4
EndochondralOssifcation – Fig.

As the primary ossification enlarges, osteoclasts break down spongy bone & form medullary cavity


Ossification of epiphyses - development of secondary ossification centers in epiphyses; cartilage begins to become bone - when complete cartilage remains only at epiphyseal surfaces (articlular cartilage) and at the epiphyseal plate

endochondral ossifcation fig 6 5
EndochondralOssifcation – Fig. 6-5

Bone growth continues during infancy & youth

- long bones lengthen at epiphyseal plate

- long bones thicken by a process called

appositional growth (inside breaks down at a

slower rate than exterior builds up)

- some facial bones (nose, mandible) grow

throughout life

the skeleton 206 bones
The Skeleton – 206 bones

Axial skeleton – forms long axis of body & includes the bones of the skull, vertebral column, and rib cage

Appendicular skeleton – bones of upper and lower extremeties and girdles (shoulder/hip)

the axial skeleton 80 bones
The Axial Skeleton – 80 bones

A. Skull – body’s most complex bony structure – Fig. 6-8

1. Cranial bones (8)

a. site of attachment of head muscles

b. enclose & protect brain & organs of hearing & equilibrium

the axial skeleton 80 bones1
The Axial Skeleton – 80 bones

2. Facial bones (14)

a. form framework of face

b. hold eyes in an anterior position

c. provide cavities for the organs of taste &

smell and openings for the passage of air

& food

d. secure teeth

e. anchor the facial muscles of expression

the axial skeleton 80 bones2
The Axial Skeleton – 80 bones

3. Middle ear bones (6) – used in sense of hearing

the axial skeleton 80 bones3
The Axial Skeleton – 80 bones

4. Sutures – interlocking joints of skull bones

the axial skeleton 80 bones4
The Axial Skeleton – 80 bones

B. Vertebral column – 26 irregular bones that form a flexible curved rod that supports the body trunk

1. Provides attachment points for ribs &

muscles of back

2. Division of spine – curvature increases

strength, resilience & flexibility of spine,

making it function like a spring rather than

a rod

the axial skeleton 80 bones5
The Axial Skeleton – 80 bones

C. Thorax – 12 pairs of ribs (both male & female),

sternum, thoracic vertebrae, costal cartilage

1. Forms protective cage around thoracic


2. Supports shoulder girdles & upper limbs

3. Provides attachment points for the muscles

of the back, chest, & shoulders

4. Intercostal spaces – occupied by inter-

costal muscles which elevate & depress

during breathing

the appendicular skeleton 126 bones
The Appendicular Skeleton 126 bones

A. Adapted to carry out movement

B. Pectoral (shoulder) girdle – clavicle, scapula

C. Arm/hand – humerus, radius, ulna, carpals, metacarpals, phalanges

D. Pelvic girdle – coxal bones (ilium, ischium, pubic)

E. Leg/feet – femur, tibia, fibula, patella, tarsals, metatarsals, phalanges

male female skeletal differences
Male & Female Skeletal Differences

A. Most male skeletons are larger (no great functional importance)

B. Structural difference in pelvis

1. Male - narrower

2. Female – structured to cradle baby; broader, shallower,

lighter, rounder

C. Pelvic brim

1. Male – basically heart shaped

2. Female – wider, oval from side to side

D. Coccyx

1. Male – narrow, longer; less movable; curves


2. Female – wider, shorter; more movable; straighter

articulations joints
Articulations (joints)
  • Two different ways to classify

Structural classification – based on material that binds




Functional classification – based on amount of movement


Synarthroses – immovable joints; fibrous connective tissue grows between the articulating bones; - ex. Sutures of cranial bones


Amphiarthroses – slightly moveable; cartilage or fibrous tissue connects articulating bones – ex. Symphysis pubis, ligaments, fibrous membrane between radius & ulna


Diarthroses – allow considerable movement; Fig. 6-20, 6-21, Table 6-7

1. Ball & socket

a. shoulder & hip joints

b. this type of joint permits the widest

range of motion

  • Diarthroses – allow considerable movement; Fig. 6-20, 6-21, Table 6-7

2. Hinge joints

a. elbow & knee, fingers, toes

b. movement in 2 directions – flexion

(bending), extension (straightening)


Diarthroses – allow considerable movement; Fig. 6-20, 6-21, Table 6-7

3. Pivot joint

a. small projections of one bone pivots

in an arch of another

b. C2 (axis) projection pivots in arch of

C1 (atlas); allows rotation of the



Diarthroses – allow considerable movement; Fig. 6-20, 6-21, Table 6-7 

4. Saddle Joint – only 1 pair

a. between metacarpal bone of thumb

& carpal bone of the wrist

b. produces great mobility (opposable thumb);

  • flex & extend
  • Abduct – moving away from midline
  • Adduct – moving toward midline
  • Circumduct - circle

Diarthroses – allow considerable movement; Fig. 6-20, 6-21, Table 6-7

5. Gliding – flat surfaces

a. least movable of all diarthrotic joints

b. joint between vertebrae or between

& carpal/tarsal bones


Diarthroses – allow considerable movement; Fig. 6-20, 6-21, Table 6-7

6. Condyloid joints (ellipsoid)

a. condyle fits into an elliptical socket

b. ex. – distal end of radius & carpal

bones or

femur &