The brain, spinal cord and optic nerves are connected to one another by nerves and nerve fibers. A protein coating called myelin surrounds and protects the nerve fibers. When myelin becomes inflamed or is destroyed, this is called demyelination, the result is an interruption in the normal flow of nerve impulses through the central nervous system. The process of demyelination and subsequent disruption of nerve impulse flow is the disease known as MS.

Injured tissue called lesions or plaques form in areas of demyelination. In many cases, the cells that create myelin are destroyed, as are the nerve fibers. The body is not able to heal the myelin or nerve fibers, which further contributes to disability.

Generally, MS follows one of four courses, which are called:

• Relapsing-remitting - Where symptoms may fade and then recur at random for many years
• Secondary progressive - Which initially follows a relapsing-remitting course and later becomes steadily progressive
• Primary progressive -  Where the disease is progressive from the start
• Progressive relapsing  Where steady deterioration of nerve function begins when symptoms first appear. Symptoms appear and disappear, but nerve damage continues