backbone
(BAK-bone)
The bones, muscles, tendons, and other tissues that reach from the base of the skull to the tailbone. The backbone encloses the spinal cord and the fluid surrounding the spinal cord. Also called spinal column, spine, and vertebral column.
Enlarge this image in new windowAnatomy of the spine. The spine is made up of bones, muscles, tendons, nerves, and other tissues that reach from the base of the skull near the spinal cord (clivus) to the coccyx (tailbone). The vertebrae (back bones) of the spine include the cervical spine (C1-C7), thoracic spine (T1-T12), lumbar spine (L1-L5), sacral spine (S1-S5), and the tailbone. Each vertebra is separated by a disc. The vertebrae surround and protect the spinal cord. The spinal cord is divided into segments, each containing a pair of spinal nerves that send messages between the brain and the rest of the body. Many spinal nerves extend beyond the conus medullaris (the end of the spinal cord) to form a bundle of nerves called the cauda equina.