Between each vertebrae in the neck (cervical vertebrae) is a piece of gelatinous material called the cervical disc which is the shock absorber of the head and neck. It acts like a cushion between the vertebrae. There are normally six discs in the neck (C1 through C6).
As we get older, the discs gradually become dry and flattened which is called "dessication". Eventually, the disc space becomes narrower and the vertebrae begin to touch each other. This is known as degenerative disc disease. The narrower the space between the vertebrae, the less room the nerve has to travel. The nerves may then become irritated, resulting in pain, numbness, tingling or weakness.