Damaged nerves have scar tissue all over them. Multiple sclerosis causes the immune system to attack the nerves' myelin sheath, leading to the formation of scar tissue.
Myelin is the fatty substance that surrounds the nerve fibers in people's brains, spinal cords and optic nerves. Aside from serving as insulation, it also helps the nerves in sending electrical signals. When the myelin covering is damaged and scar tissue forms, the nerves are not able to properly transmit messages that dictate the body's speech, movement and other functions.
One symptom of nerve damage is numbness, which indicates an inability to transmit information. Others are pain and tingling, which are signs that the nerves are sending out false signals.