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MCAT Biology Question — Action Potential

Which ions are primarily responsible for repolarization of a neuron following an action potential?


a) K+ out of the neuron

b) K+ in to the neuron

c) Na+ out of the neuron

d) Na+ in to the neuron




An action potential and accompanying depolarization results from Na+ ions rushing down their concentration gradient in to the cell. The repolarization is caused predominantly by a rush of K+ ions down their concentration gradient out of the cell.

a) K+ out of the neuron, correct.

b) K+ in to the neuron, incorrect, This would require K+ ions to flow contrary to their concentration gradient.

c) Na+ out of the neuron, incorrect, The Na+/K+ ATPase pumps Na+ out of the neuron, Na+ will not spontaneously flow out of the neuron.

d) Na+ in to the neuron, incorrect, Na+ in to the neuron accompanies depolarization, not repolarization.

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