Question

Which of the following does NOT happen during an action potential?

A. A change in permeability of the membrane to sodium

B. A change in permeability of the membrane to potassium

C. A transient increase in the sodium current

D. A sustained decrease in the potassium current

E. A self-activating, self-perpetuating rise in sodium current

Answer 1

D. A sustained decrease in the potassium current.

Note: There are five stages of action potential across the cell membrane:

1. In resting state the neurons have resting potential which is negative inside than outside. This negative membrane potential is maintained by sodium potential pump and potassium leak channels.
2. Once depolarization occurs, voltage gated sodium channels opens to allow influx of sodium ions to make membrane potential positive.
3. The membrane potential depolarizes to the threshold level by increase in the sodium current.
4. Hyperpolarization occur when potassium channel open and sodium channel close. This allows potassium to leak out of the cell making the membrane potential negative.
5. Finally repolarization occurs thereby closing the potassium channels. As a result, the membrane potential resumes the resting membrane potential.