Found this for you on line
'The backbone, or spine, is composed of a series of connected bones called "vertebrae." The vertebrae surround the spinal cord and protect it from damage. Nerves branch off the spinal cord and travel to the rest of the body, allowing for communication between the brain and the body. The brain can send a message down the spinal cord and out through the nerves to make the muscles move. The nerves also send information such as pain and temperature from the body back to the brain.
The vertebrae are connected by a disc and two small joints called "facet" joints. The disc, which is made up of strong connective tissues which hold one vertebra to the next, acts as a cushion or shock absorber between the vertebrae. The disc and facet joints allow for movements of the vertebrae and therefore let you bend and rotate your neck and back.
The disc is made of a tough outer layer called the "annulus fibrosus" and a gel-like center called the "nucleus pulposus." As you get older, the center of the disc may start to lose water content, making the disc less effective as a cushion. As a disc deteriorates, the outer layer can also tear. This can allow displacement of the disc's center (called a herniated or ruptured disc) through a crack in the outer layer, into the space occupied by the nerves and spinal cord. The herniated disc can then press on the nerves and cause pain, numbness, tingling or weakness in the shoulders or arms. Your doctor may test for changes in the reflexes, sensation and strength in your arms caused by the herniated cervical disc. Rarely, the herniated disc may put pressure on the spinal cord, causing problems in the legs as well.'
The last sentence sounds like what is happening to your dad