Anatomy and Physiology / Unit 4: The Skeletal System
4.4 The Axial Skeleton
Notes
The axial skeleton (80 bones) forms the long axis: skull, vertebral column, thoracic cage.
- Skull: 8 cranial bones (frontal, 2 parietal, 2 temporal, occipital, sphenoid, ethmoid) and 14 facial bones (including the mandible, maxillae, zygomatics, nasal). The mandible is the only movable skull bone (except ear ossicles). Sutures are immovable joints between skull bones. The foramen magnum in the occipital bone passes the spinal cord.
- Vertebral column: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral (sacrum), 3-5 fused coccygeal (coccyx). Curves: cervical and lumbar curve inward, thoracic and sacral curve outward. Abnormal curves: scoliosis (lateral), kyphosis (exaggerated thoracic), lordosis (exaggerated lumbar).
- Thoracic cage: sternum plus 12 pairs of ribs. Ribs 1-7 are true ribs; 8-12 are false ribs (11-12 are floating).
- Atlas (C1) holds up the skull; axis (C2) has the dens that lets the head rotate.
Practice
How many thoracic vertebrae does the human spine have?
There are 7 cervical, 12 thoracic and 5 lumbar vertebrae, plus the fused sacrum and coccyx.
A person has an abnormal sideways curve of the spine. This condition is:
Scoliosis is a lateral curvature.
A blow to the back of the head damages the bone through which the spinal cord passes. Which bone is it?
The foramen magnum is in the occipital bone.
Ready for more? Take the Unit 4 test.