Download 4.2 Axial skeleton

Chapter 4
Skeletal System
4.2 The Axial Skeleton
- skeleton divided into two major areas
1. Axial – head, trunk
2. Appendicular – arms and legs
A. Skull - 22 bones
1. Divided into two groups
a. Cranium (8)
1. Frontal
- forehead
2. Parietal (2)
- sides and top
3. Temporal (2) - temples
4. Occipital
- back
5. Ethmoid
- inside nasal cavity
6. Spheniod
- butterfly shaped bone (back of the orbits, roof of mouth,
side near temporals
b. Facial (14)
1. Maxillary (2) - upper jaw (top teeth)
2. Palatine (2) - posterior part of hard palate
3. Zygomatic (2) - cheekbones
4. Lacrimal (2) - in orbits, surround tear ducts
5. Nasal (2)
- bridge of nose
6. Mandible
- lower jaw, articulated (bottom teeth)
7. Vomer
- bony nasal septum
8. Inferior Concha (2) – internal nasal cavity
c. Sutures (Cornonal, Sagittal, Lambodoidal)
1. bones of skull and face are held together by sutures
2. joints bind the bones together with tiny fibers
3. permit small amount of movement (elasticity of the skull)
d. Foramen magnum (hole)
B. Vertebral Column (Spine) – 33 bones
1. Regions of the Spine (5)
a. Cervical (7 bones of neck)
1. first 2 cervical vertebra – the Atlas and the Axis – allow head to nod up/down
and rotate from side to side
2. Atlas is modified to connect the occipital bone of cranium to the spinal column
3. Axis is modified with odontoid process – allows rotation of atlas
b. Thoracic (12) – chest region - articulate to the ribs
c. Lumbar (5) – lower back
d. Sacrum (5 fused bones) – posterior region of pelvic girdle
e. Coccyx (4 fused bones) – “tail bone” – located at the end of the spine
2. Structures of the Vertebrae
a. all vertebra are unique (no two the same)
b. whereas all vertebrae are unique they all share common structural features
1. vertebral body – thick disc, weight bearing, anterior portion
2. vertebral arch – bone projection around vertebral foramen, posterior portion
3. transverse processes – bony projections on the sides of the vertebrae
4. spinous processes – bony projection, extends posteriorly
5. superior/inferior articular proceses – indentations where vertebrae join from
above and below (facet joints)
c. size of the vertebrae increase from top to bottom – load bearing (pyramid)
- Cervical only support head and neck
- Thoracic supports head, neck, chest, arms
- Lumbar supports head, neck, chest, arms, abdominal area
3. Spinal Curves – alternating curves make spine stronger/better able to resist forces
a. thoracic and sacral curves – primary spinal curves (anterior concave)
b. lumbar and cervical curves – secondary spinal curves (posterior concave)
c. coccyx curve – (anteriorly concave)
d. abnormal curves
1. lordosis – exaggeration of lumbar curve
2. kyphosis – exaggeration of thoracic curve
3. scoliosis – lateral deviation
4. Intervertebral Discs
a. discs are fibrocartilage – provide cushioning of the articulated vertebrae (no fused)
b. allow the spine to bend
c. anterior and posterior thickness differential create the spinal curvatures
d. normal adult – discs account for a quarter of spine height
- discs absorb water at night – you are taller in the morning (1/4 to ¾ of an inch)
- injury and aging disrupt water retention
- discs receive no blood supply – uses movement to flush wastes and bring in blood
Fixed body position limits pumping action and affects disc health (long periods of
sitting)
C. The Thoracic Cage (Bony Thorax) – 12 pairs of ribs, sternum
1. Composed of ribs, sternum and vertebrae = thoracic cage (bony) to protect the heart
and lungs.
2. Sternum is divdied into 3 parts
a. manubrium = upper sternum, articulations to the left and right clavicle (collarbone)
and to first and second pairs of ribs
b. body = middle portion of sternum, articulations for 8 pairs of ribs
c. xiphoid process = bottom of sternum (no ribs attached)
3. 12 pairs of ribs
a. first 7 pairs attach directly to the sternum = called true ribs
b. pairs 8,9, and 10 = false ribs, cartilage attachments to the 7th rib, NOT to sternum
c. 11th and 12th pairs of ribs = floating ribs – do not attach to the front of the body
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