The brain is the body's control center. Each part of the brain controls specific functions. These include movement, balance, sensation, and thinking. The brain controls these by sending and receiving messages through nerves. Nerves have a protective covering. The covering is called myelin. With MS, the myelin on nerves in the brain and spinal cord is damaged. The loss of this covering causes messages moving along affected nerves to slow or stop. This results in MS symptoms.