A herniated disc occurs when the outer portion of a spinal disc breaks down and the inner potion leaks out.The inner portion of the disc that extrudes can then irritate or compress nearby nerves, causing radiating pain.

A spinal disc acts as a shock absorber between the vertebrae of the spine, and allows for movement in the spine. The durable outer portion of a disc, called the annulus fibrosus, serves to contain the soft inner portion of the disc, the nucleus pulposus.