Q CLINICAL CASE REPORT Chapter 12 Running Problem: Periodic Paralysis 1) When Na+ channels on the muscle membrane open, which way does Na+ move? 2. What effect would continued movement of Na+ have on the membrane potential of muscle fibers? 3. 3) What ion is responsible for the repolarization phase of the muscle action potential, and in which direction does this ion move across the muscle fiber membrane? How might this be linked to hyperKPP? 4. 4) Explain why a Na+ channel that does not inactivate results in a muscle that cannot contract (flaccid paralysis).