The intervertebral disc is water based fluid structure that is between vertebras. This make-up permits motion. It acts as both a separator and a shock-absorbing mechanism. A disc is composed of 2 parts: a central nucleus (pulposus) surrounded within an annulus (fibrosus).

The nucleus has properties of jelly. When warm, it is fluid. When it is cold, it is semi-solid. The annulus is tough, like a burlap sack, and is in layers. Each layer is at an alternating angle too. So the pattern looks like X's. The weakest portion of the disc is the posterorlateral (back outside) portion.