Discs are located between each vertebra and provide flexibility and shock absorption for the spine. The thick fibrous outer disc wall, know as the annulus fibrosus, surrounds a jelly-like center, called the nucleus pulposus. Discs undergo tremendous amount of stress, which can sometimes lead to a bulging disc, a weakening of the disc wall, that cause the disc to bulge out and press painfully on surrounding nerves. A herniated disc occurs when the pressure within a disc becomes too great, treating through the disc wall (annulus fibrosus), allowing a portion of the nucleus pulposus to protrude. The escaped nucleus pulposus may then impinge painfully on nerve roots, leading also to numbness, tingling, and / or muscle weakness associated with the condition of sciatic pain. The illustration below gives a bird's eye view of what exactly is going on when a disc bulges or herniates.