The spine is made up of cylindrical bones called vertebrae. Between the bones of the spine are small discs made of a thick layer of cartilage on the outside and a soft, jelly-like material on the inside. The discs act to absorb shocks caused when the spine moves, and they allow the spine to bend.
The spinal cord is a bundle of nerves running through the canal within the spinal column. It carries messages to and from the brain via nerve roots that branch out to the body along the length of the spinal cord. The nerves exit the spine through small openings on each side; these are called foramens (singular foramen; foramina is also used for the plural), after the Latin word for "window."
If a foramen becomes narrowed by arthritis or a bulging disc, pressure on the nerve can cause numbness and pain, and even muscle weakness if severe enough. A herniated, prolapsed, or ruptured disc happens when the inner material bulges or bursts through the outer lining of cartilage and puts pressure on or damages the spinal nerves or the spinal cord.
Herniated discs can occur in any part of the spine, but they are most common in the neck (cervical spine) and lower back (lumbar section of the spine). Herniated discs are more common in people between 30 and 40 years old, but they can occur at any age. Studies have shown that even some teenagers can be affected.