About the Spine
The spinal column is composed of 33 bones called vertebrae. While the shapes of the bones differ in different areas of the spine, the basic design is constant at all levels. A cylinder of bone called the vertebra body lies to the front. Behind this is a bony arch (lamina) enclosing the spinal canal. The spinal cord and nerves run down through the spinal canal. The arches of adjacent vertebrae that lie behind the spinal canal are in contact with one another through joints, called facets. The cervical spine (neck) and lumbar spine (low back) account for most of the flexibility of the spinal column. The thoracic spine (chest) is significantly stiffer, due largely to the attachment of the ribs that limit the amount of motion in this segment of the spine.
The intervertebral discs lie to the front of the spinal cord, between the vertebral bodies. They are composed of an outer fibrous capsule (annulus). The inner contents (nucleus pulposus) have a high protein and water content and act like a gel. This allows the disc to act as a shock absorber allowing the vertebral bodies to move within certain limits in relation to each other. The spinal nerves exit the spinal canal though small windows between neighbouring vertebrae.