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The Spine consists of the 33 vertebra, classified into five groups: cervical spine, thoracic spine, lumbar spine, sacrum, and coccyx.
- Cervical region consists of seven vertebrae (C1 through C7)
- Thoracic region consists of twelve vertebrae (T1 through T12)
- Lumbar region consists of five vertebrae (L1 through L5).
- Sacral region consists of five vertebrae, all fused together to form one continuous bone mass known as the sacrum.
- Coccygeal region consists of four vertebrae, all fused together to form the coccyx or tailbone.
The uppermost 24 vertebrae are separated from one another by fibrous cartilage pads, called intervertebral discs which allow the spine to bend and act as shock absorbers during activity. The disc has a hard shell on the outside (annulus fibrosis) and a soft interior (nucleus pulposus) which is the consistency of shrimp meat. In the lowest part of the spine, the vertebrae are naturally fused to form the sacrum and the coccyx (tail bone).Protruding from the back of each block-like vertebral body is an arch of bone that helps to form the large, vertical spinal canal, which surrounds the spinal cord and nerve bundles. A fluid-filled protective membrane, the dura, covers the contents of the spinal canal from where the cord begins at the base of the brain to where it ends (in a bundle of nerve fibers known as the cauda equina).
A pair of spinal nerves branches at each vertebral level (one to the left and one to the right), providing sensation and movement to all parts of the body. Three large bone processes arise from the vertebrae's arch-one to each side (transverse) and one straight toward the back of the body (spinous). Strong ligaments and muscles attached to the vertebrae both support the spine, further protect the delicate spinal cord and nerves inside, and allow for a remarkable degree of motion.
