A bulging disk occurs when the nerve roots exiting the spine are pressed on, or compressed, causing pain and other neurologic problems such as numbness, burning, and weakness.
If you were to interview 100 percent of people with back pain and them what the cause of their condition was, 90 would probably say that the cause of their pain was due to a "slipped disk" or a "herniated disk" in their back. Before we get into more detail of what a bulging disc is, here is what it isn't.
Herniated discs, slipped discs, and bulging discs are three types of spinal conditions that describe the results of degenerative disc disease. Degenerative disc disease occurs when one of more of the intervertebral discs of the spine age or suffer damage. Discs may degenerate or become damages at either their outer envelope made of overlapping bands of fibers, or at their inner core, which is composed of water, and a goopy mixture of glycoproteins and nutrients. The job of the outer envelope, known as the annulus fibrosus is to hold the general shape of the disc and allow for some movement, such as when pressures are exerted on the spine, while resisting tearing of its walls. The annulus fibrosus allows for some absorption and excretion through its walls, so that the inner parts of the discs may take on and expel water and nutrients as needed. The Inner core, or nucleus of the discs has a gel-like consistency, and is composed of water, among other substances. This mixture helps the disc to act as a shock absorber when we put extra weight on our spine as we sit up, stand, and move through space.
Spinal discs do not rupture or slip, as the term "slipped disc" would have you assume. Our intervertebral discs, when they do become degenerated, shrink downwards vertically in height, as occurs when the interior lose their ability to retain water, and outwards, in the event of a herniated or bulging disc. A herniated disk is a more severe form of a bulging disk, that occurs when the outer envelop if the disk (annulus fibrosus) becomes thin, or worn, and the disc loses its ability to hold its original shape. If the wall of the disk becomes worn and thin along its border, it may begin to bulge outwards. This condition is known as a bulging disk. If the wall of the disk becomes torn entirely, the condition is known as a herniated disk.
Both herniated disks and bulging disks may cause back pain or other sensory deficits (e.g. burning, tingling, loss of feeling) if the material coming away from the disc presses on the adjacent nerve root. In the event of a bulging disk, the wall of the disk bulges outwards to press onto the nerve. In the event of a herniated disk, the tear in the annulus creates a hole big enough for parts of its nucleus of material to ooze outwards. Patients may experience pain as a result of a herniated disk if the material coming out of the tear presses into the adjacent nerve root.
Like a herniated disk, a bulging disk can also come into contact with a ligament or nerve root. The result of this direct pressing on the nerve or ligament is the firing of pain signals. When the involved nerve is compromised, the result may also be muscle spasms of the nearby back muscles as well as the muscles that that nerve supplies branches to.