Spine

Spine, spinal column orvertebral cord, vertical structure of bone, nerves and nerve fibers, ligaments, and cartilage that act as a skeletal support and transmission center for the nervous system in vertebrate animals. Vertebrae are the flexible, bony joints that make up the spinal column; they number 33 in humans. The spinal cord, where bundles of nerve fibers are found, is encased in the spinal column. The human spine extends from the brainstem to the tailbone region, or coccyx. Sensory impulses travel up the spinal column to the brain; in turn, the brain sends its commands down the spinal column to voluntary muscles used for motion and balance. Paralysis occurs when an injury to the spine interrupts the transmission of these messages between the brain and limbs.

See also: Skeleton.