Between each vertebra is a disc that serves to cushion the vertebrae and connect them together in a flexible way. Over the entire spine, there are 23 discs, which make up about a quarter of the height of the spine above the sacrum. The discs are larger in the lower back, where they have to support more weight, than in the neck, where they support less weight.
The intervertebral discs are filled with gel-like material on the inside (the nucleus pulposus) and surrounded by a fibrous tough outer layer (the annulus).
When a disc herniates or ruptures, the soft nucleus spurts out through a tear in the annulus. This can press on a nerve root. The amount of pain that a ruptured disc creates depends on how much of the nucleus breaks and presses on a nerve or whether the nucleus stretches the outer annulus.
At birth, 80% of our discs are made up of water. Over time, with use and age, the spinal discs lose their water. As this happens, a disc can lose height. The discs become stiffer and less able to adapt to pressure when we move. Sometimes this can be painful. Because the discs have a poor blood supply, it is almost impossible to regenerate, repair or restore the height of the disc.