The Axial Skeleton

1. The Axial Skeleton

2. the axial skeleton = 80 bones of the head, neck, & trunk

3. SKELETAL ORGANIZATION • skull = cranium + facial bones • hyoid bone = supports the tongue • vertebral column = vertebrae + sacrum + coccyx • thoracic cage = ribs + sternum

4. THE SKULL 22 bones (8 cranial + 14 facial)

5. the mandible is the only movable bone of the skull • rest are immovable & joined by sutures • coronal suture • sagittal suture • lambdoid suture • squamous suture

6. 8 cranial bones: • 1 frontal bone forms your forehead, contains sinuses • 2 parietal bones form the top / sides of your head

7. 1 occipital bone forms back of head • contains foramen magnum where spinal cord passes to connect to brain

8. 2 temporal bones help form the side & base • external auditory meatus leads to the inner ear

9. 1 sphenoid bone is interior, contains sinuses, shaped like a butterfly • cradles the pituitary gland

10. 14 facial bones: form the face’s shape & provide a place of attachment for muscles that move the jaw & control expression • 2 maxillae form the upper jaw w/ teeth & hard palate • contain the maxillary sinuses

11. 2 palatine bones help form the hard palate & nasal cavity

12. 2 zygomatic bones “cheekbones”, help form eye orbits

13. 2 nasal bones form the bridge of the nose

14. 1 mandible = movable lower jaw, contains teeth

15. some cranial bones have air-filled cavities called sinuses • lighten skull • enhance resonance of voice

16. Skull Development • the infant skull contains fontanels, or soft spots where the cranial bones aren’t completely joined together • the proportions are not the same as an adult, small face & big forehead

17. The hyoid bone • acts as a movable base for the tongue • plays a role in speech & swallowing

18. THE VERTEBRAL COLUMN • extends from skull to pelvis • made of vertebrae separated by intervertebral discs • supports head & trunk, protects spinal cord, provides a place for ribs & back muscles to attach

19. 4 curvatures of the spine: • cervical & lumbar are concave • thoracic & sacral are convex • gives the spine “spring” • abnormal curvatures: • scoliosis = “twisted disease” • kyphosis = “hunchback” • lordosis = “swayback”

21. 7 cervical vertebrae in the neck (C1 – C7) • Atlas (C1) - supports the head • Axis (C2) - has a dens on which the atlas pivots • vertebra prominens •   (C7) - easily felt •   landmark at back of neck

22. 12 thoracic vertebrae (T1 – T12) articulate with the ribs • increasingly larger than the cervical vertebrae to bear more weight • spinous process points down

23. 5 lumbar vertebrae (L1-L5) at the small of the back are even larger for weight-bearing

24. sacrum=5 fused vertebrae • triangular • nerves & blood vessels pass through holes • articulates with the pelvic bones

25. coccyx= “tailbone” made from 4 fused vertebrae • acts as a shock absorber

26. THE THORACIC CAGE • includes ribs, thoracic vertebrae, sternum, costal cartilages • functions: supports pectoral girdle & upper limbs, protects the heart & lungs, aids breathing

27. ribs – 12 pairs • 7 pairs of true ribs join the sternum directly via costal cartilage • 5 pairs of false ribs (pairs 8-12) • pairs 8-10 attach to 7th rib’s costal cartilage • pairs 11 & 12 don’t attach at all; called floating ribs

28. sternum = flat, elongated bone with 3 parts (manubrium, body and xiphoid process) • articulates with the clavicles • costal cartilages of the ribs attach to it