Gel-filled discs cushion the spaces between the cervical vertebrae, the bones that protect the spinal cord in the neck area. If the disc is damaged, it can bulge or herniate into the spinal canal and compress the nerve closest to the defect.

The spinal cord is made up of nerves that relay messages back and forth between your brain and muscles and other tissues. It is protected by the backbone which is made up of stacked bones known as vertebrae. Spinal cord compression occurs anywhere from the neck to the lower end of the spine.

Multiple sclerosis is an autoimmune disease that causes demyelinization of nerve coverings over parts of the brain and spinal cord. Multiple sclerosis, or MS, affects women more often than men, and usually occurs between the ages of 20 and 40, notes the Merck Manuals Online Medical Library.

The ulnar nerve originates in the neck and runs through the shoulder, upper arm and forearm before ending in the ring and little fingers. Injuries most commonly occur at the elbow and wrist but can occur anywhere along the nerve's path.

Spinal stenosis results when the bony canal through which the spinal cord courses becomes narrowed and compresses the spinal cord. Although spinal stenosis most commonly occurs in the neck and lower back regions, it uncommonly involves the thoracic spine in the upper and middle back.

The bones in the neck region of the spine, known as cervical vertebrae, are numbered 1 to 7 beginning from the top. Discs serve as cushions between the vertebrae. The C3 and C4 disc -- commonly noted as C3-C4 -- is between the third and fourth cervical vertebrae.