Which one of the following is the correct sequence of events that correlates to the 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) 1, 2, 4, 3
c) 4, 1, 3, 2
d) 2, 1, 4, 3
e) 2, 1, 3, 4

the correct sequence of the events happened during nerve impulse is (d): 2,1,4,3

Explanation:

Originally K+ ions remains inward the membranes while Na+ ions remains outward to maintain a resting potential of membrane.

Upon stimuli Sodium channels open on membrane and Na+ diffuses inward leading to the depolarization of membrane that is it becoming more positive due to Na+ and K+ ions.

To regain it polarized state or in repolarization state Potassium channels open and K+ begun to diffuse outward while Sodium channels gets closed and Na+ ions remains inside the membrane.

Potassium channels are not efficient as compared to Sodium Channels, so an excess amount of K+ion move outward so Hyperpolarization state achieved.

As the both ions are on the wrong side and will not be available for the next nerve impulse. Hence in Refractory period by the help of Na+/K+ pum, both ions move back to their original place and membrane achieve its resting membrane potential state.