Structures of the Spine
The term “spine” or “backbone” refers to the bony structures and soft tissues of the vertebral column. The vertebrae are the bony segments surrounding and protecting the soft tissue of the spinal cord and nerve roots serving different regions of the body. Technically, the spine consists of 33 vertebrae, although some of the structures of the lower back and tailbone are fused together.
In addition to its function in structural support of the body, the vertebral column also serves as the housing for the spinal cord. The spinal cord sends signals to and from the brain along the millions of nerves and nerve pathways. Motor nerves carry impulses from the brain to the body, controlling movement. Sensory nerves travel from the body to the brain where the brain interprets the sensation, such as heat, cold, and pressure. The vertebral canal, which houses the spinal cord, is formed by the alignment of openings at the center of each vertebra. Ligaments and muscles of the back hold the vertebral column in place, and discs provide cushioning between each vertebra.
The discs are composed of two components, the tough, fibrous outer shell and a soft, jelly-like inner core. The discs function as shock absorbers, allowing the back to move freely within its normal range of motion and reducing the forces against the vertebral bones and nerves. The nerve root is the segment of the nerve that exits the spinal column.
Specific structures of the vertebral column are referenced according to anatomic regions. For example, there are seven cervical or neck vertebrae. The very first or top cervical vertebra supports the skull and is called the atlas. Just beneath the cervical vertebrae are the 12 vertebrae of the thoracic, or chest, region. The next lower region is called the lumbar, or lower back region, which contains five vertebrae. The sacral, or buttocks, region contains five vertebrae, which are fused into one vertebral structure. Similarly, the vertebrae of the coccygeal region are fused into a single structure, the tailbone.