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The anterior and posterior part of each vertebra are connected around a circular space. Since all the vertebrae are aligned one over the other one, they form a tunnel that starts at the level of the neck and ends in the pelvis.
This tunnel is called vertebral canal and it follows the different curves of the column. The vertebral canal is large and triangular in the cervical and lumbar part, while it is small and rounded in the thoracic region, where the motion is more limited. The vertebral canal contains the spinal cord, which occupies the upper two-third of the canal and spinal nerves that spring from the spinal cord.
The spinal cord is a longitudinal cord of nerve tissue that serves not only as a pathway for nervous impulses to and from the brain, but as a centre for carrying out and coordinating many reflexes and actions independently of the brain.
The cord comes off the base of the brain, runs throughout the cervical and thoracic spine and ends at the lower part of the thoracic spine. The spinal cord does not run through the lumbar spine, it stops in the lower thoracic spine, the nerve roots come off the bottom of the cord like a horse’s tail (cauda equina). In each level of the spine a pair of nerve roots branch off from the spine through foramen, which are bony pathways for the roots to exit from the spine.
The spinal cord is surrounded by a membrane, the dura mater. Between the dura mater and the cord, there is a fluid that protects the spinal cord.
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