Question 6. [10 points] Line 1 (green) shows tetanus, line 2 (blue) shows incomplete tetanus and line 3 (orange) shows action potential. Part A [6 points] Describe in detail how an action potential is propagated. (A complete answer will include the distribution of ions before the action potential; where and how they move; the direction of propagation) Part B [4 points] Multiple sclerosis (MS) is a disease in which the myelin sheath is damaged. A common symptom of MS is muscle weakness. Describe the function of the myelin sheath. Tell how damage to the myelin sheath may result in the symptom of muscle weakness..