The bones (vertebrae) that form the spine in the back are cushioned by discs. These discs are round, like small pillows, with a tough, outer layer (annulus) that surrounds the nucleus. Located between each of the vertebra in the spinal column, discs act as shock absorbers for the spinal bones.
A herniated disc (also called bulged, slipped or ruptured) is a fragment of the disc nucleus that is pushed out of the annulus, into the spinal canal through a tear or rupture in the annulus. Discs that become herniated usually are in an early stage of degeneration. The spinal canal has limited space, which is inadequate for the spinal nerve and the displaced herniated disc fragment. Due to this displacement, the disc presses on spinal nerves, often producing pain, which may be severe.
Herniated discs can occur in any part of the spine. Herniated discs are more common in the lower back (lumbar spine), but also occur in the neck (cervical spine). The area in which pain is experienced depends on what part of the spine is affected.