There are different classifications of disc pathology. The main two are herniations and bulges. Of the two, herniations are more sever and require a longer healing process. The disc itself is comprised of a nuclear material (the Nucleus pulposus) and the outer fibers (the annulus fibrosus). An easier way to explain the structure is with a popular American staple, the jelly doughnut. The inside/nucleus of the disc has a pliable/squishy substance similar to jelly. The outer portion of the disc, annulus, has a more rigid structure like the cake in the doughnut.
In the human body this substance is more like grizzle from a steak. When a disc herniates, tears in the annular fibers are formed and the nucleus (jelly) passes through this structure and extends passed the outer most fibers. When this herniation is severe enough it can compress the spinal nerve and cause an array of problems that can extend into the lower extremity (radiculopathy /sciatica). A disc bulge is less severe; however, since the disc is a pain sensitive structure pain is felt. With a disc bulge tears in the outer fibers are present and the nucleus extends into the annular fibers. This causes an inflammatory response and the disc “bulges” taking on a physiological different shape.