The spinal discs rest between the bones of the spine to provide comfort and movement. These discs are composed of an outer membrane that is filled with an inner cushion of collagen and water. Disc injuries are caused by trauma, degeneration, or may occur without any obvious cause. Such injuries, which are most often experienced in the neck and the lower back, signify that inner disc material is protruding from its protective shell and affecting the spinal nerves. When the disc herniates, the outer membrane ruptures and allows its contents to move outward and closer to the spinal cord.