An intervertebral disk acts as shock absorber between each of the vertebrae in the spinal column by keeping the vertebrae separated when there is impact from activity. They also serve to protect the nerves that run down the middle of the spine and intervertebral disks.
There are a total of 24 disks in the human spine. The disks are made of fibrocartilaginous material. The outside of the disk is made of a strong material called the annulus fibrosus. Inside this protective covering is a jelly-like substance known as mucoprotein gel. This interior is known as the nucleus pulposus. As the spine receives pressure, the gel moves inside the annulus fibrosus and redistributes itself to absorb the impact of the pressure. The mucoprotein gel loses moisture as a person ages and the spine is able to absorb less shock. The outer layer of annulus fibrosus on the intervertebral disk deteriorates with age and can begin to rip, and this causes chronic back pain for some people.