The human spine provides protection, support and shape. It provides protection for the spinal cord. It is a site of muscle and bone attachment. It also is part of the bone structure that gives humans the biped form.
It is also referred to as the vertebral column. It has 33 vertebrae. In the adult human there are 24 articulating, or movable, vertebrae, and 9 fused vertebrae. In the infant, the bones of the Sacrum and Coccyx are not fused. Between them, they make up the five areas of the spine.
The Sacrum and the Coccyx account for the fixed vertebrae section, while the areas called the Lumbar, Thoracic and Cervical account for the movable sections. The movable sections of vertebrae are separated by intervertebral discs. These allow the join to move and also bind each vertebra together.
Looking at the five sections of the spine in order, the top to bottom:
The Cervical area has seven vertebrae; from C1 to C7. It is most flexible part of the spine. It includes two specialized vertebrae: the Axis (C2) and the Atlas (C1). Both of these play a role in supporting and enabling the skull to move around. This area of the spine corresponds to neck area.
The Thoracic has twelve vertebrae (T1 to T12). The thoracic area is equivalent to the chest area. It sits between the Cervical (on top) and the Lumbar (below) vertebrae. The Cervical vertebrae are the smallest moveable vertebrae. The thoracic are mid-size and the Lumbar are the biggest. The Thoracic vertebrae join and articulate with the bones of the ribs.
The Lumbar vertebrae are five in number (L1 to L5). These are the biggest vertebraee of the movable area of the spine. They sit at the base of the spine, in between the thoracic area and the Sacrum which is also part of the pelvic girdle.
The Sacrum bone is so named because it was thought by early Christians that on the resurrection (judgement day) it would be this bone which would provide the starting point for the dead to be brought back to life. However, the use goes back further, to the offering of animal sacrifices in Roman times.
The Sacrum may look like one triangular looking bone, but is in fact fused out of five bones (S1 – S5). It is located at the base of the spinal column. It is joined with two ilium bones and the Coccyx.
The Coccyx has on average four fused parts (Co1 – Co5), though it is not that uncommon for this to vary between 3 and 5. The Coccyx is firmly fused to the bottom of the sacrum.
The Complete Gray's Anatomy. Henry Grey. (2003) Senate. Merchant Books.