Which one of the following sequences is the correct sequence of events of a nerve impulse: 1. the membrane becomes depolarized 2. sodium channels open and sodium ions diffuse inward 3. the membrane becomes repolarized 4. potassium channels open and potassium ions diffuse outward while sodium is actively transported out of the cell:
a. 3, 2, 4, 1
b. 2, 1, 4, 3
c. 2, 1, 3, 4
d. 1, 2, 4, 3