In multiple sclerosis, there is progressive and intermittent damage to the myeli

Action potentials travel faster along fibers that are myelinated than fibers that are nonmyelinated. Destruction of the myelin sheath slows the time it takes for motor neurons to communicate with their effector muscles. This delay in response results in varying degrees of uncoordinated muscle activity. The situation is very similar to a newborn, where the infant cannot control its arms and legs very well because the myelin sheaths are still being laid down for the first year of life. Since not all motor neurons to the same muscle may be demyelinated to the same degree, there would be some fibers that are slow to respond while there would be others that are responding normally, thus producing contractions that are erratic and poorly controlled.