The vertebral column (spinal column or backbone) is made of individual bones called vertebrae. The names of vertebrae indicate their location along the length of the spinal column. There are 7 cervical vertebrae, 12 thoracic, 5 lumbar, 5 sacral fused into 1 sacrum, and 4 to 5 small coccygeal vertebrae fused into 1 coccyx (Fig. 6–10).
The seven cervical vertebrae are those within the neck. The first vertebra is called the atlas, which artic-ulates with the occipital bone to support the skull and forms a pivot joint with the odontoid process of the axis, the second cervical vertebra. This pivot joint allows us to turn our heads from side to side. The remaining five cervical vertebrae do not have individ-ual names.
The thoracic vertebrae articulate (form joints) with the ribs on the posterior side of the trunk. The lumbar vertebrae, the largest and strongest bones of the spine, are found in the small of the back. The sacrum permits the articulation of the two hip bones: the sacroiliac joints. The coccyx is the remnant of tail vertebrae, and some muscles of the perineum (pelvic floor) are anchored to it.
Figure 6–10. Vertebral column. (A) Lateral view of left side. (B) Atlas and axis, superior view. (C) 7th thoracic vertebra, left lateral view. (D) 1st lumbar vertebra, left lateral view.
QUESTION: Compare the size of the individual thoracic and lumbar vertebrae. What is the reason for this difference?
The supporting part of a vertebra is its body; the bodies of adjacent vertebrae are separated by discs of fibrous cartilage. These discs cushion and absorb shock and permit some movement between vertebrae (symphysis joints). Since there are so many joints, the backbone as a whole is quite flexible.
The normal spine in anatomic position has four natural curves, which are named after the vertebrae that form them. Refer to Fig. 6–10, and notice that the cervical curve is forward, the thoracic curve backward, the lumbar curve forward, and the sacral curve back-ward. These curves center the skull over the rest of the body, which enables a person to more easily walk upright.