The spine and the spinal cord are two different structures. The spinal cord is a bundle of nerve cells and fibers running from the base of the brain to shortly above the tailbone. The spine, also called the backbone or spinal column, is the set of bones (vertebrae) that encase the spinal cord. The spine and the spinal cord are anatomically grouped into segments; the spine is divided into bone segments corresponding to each of the vertebrae, while the spinal cord is divided into neurological segments corresponding to the body functions that are controlled.
The spine has seven neck (cervical) segments or vertebrae, twelve chest (thoracic) vertebrae, five back (lumbar) vertebrae, and five tail (sacral) vertebrae. The segments are designated by a letter-number combination that corresponds to the position of the segment on the spine. For example, C1 refers to the first vertebra in the cervical area, and T3 refers to the third vertebra in the thoracic area. In total, there are seven cervical vertebrae (C1 – C7), twelve thoracic vertebrae (T1 – T12), five lumbar vertebrae (L1 – L5) and five sacral vertebrae (S1 – S5).
Spinal cord segments are named in the same fashion as the spine’s segments, but the two do not always match-up. For instance, the C1 vertebra on the spine and the C1 cord correspond to each other, but the C7 vertebra contains the C8 cord. The spinal cord does not travel the entire length of the spine; it ends at the second lumbar segment (L2). Spinal roots exit below the spinal cord’s tip (conus) in a spray; this is called the cauda equine (horse’s tail). Damage below the L2 generally does not interfere with leg movement, although it can contribute to weakness.