Answer:
Myelin sheath
Explanation:
Multiple sclerosis is a degenerative disease which is caused by the degeneration of the myelin sheath which forms a sheath around the neurons.
As a result of the degeneration of the myelin sheath which increases the speed of the transmission of the impulse, the transmission slows down and the communication of the body part with the brain slows down.
In the given question since the communication of the muscles to the body part has slowed down and muscles control might be lost therefore this is the result of the degeneration of the myelin sheath.
Thus, the Myelin sheath is the correct answer.