Nerve and muscle: after-hyperpolarisation: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Nerve and muscle: after-hyperpolarisation

Sample item

In a neurone, the membrane potential briefly falls below the resting level after repolarisation. What mainly causes this undershoot?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Slow closure of voltage-gated potassium channels

Voltage-gated potassium channels open with a delay and close slowly after the action potential, so potassium efflux continues briefly and drives the membrane closer to the potassium equilibrium potential, producing the after-hyperpolarisation. The relative refractory period partly reflects this.

Option by option

  • A. Entry of chloride through ligand-gated channels

    Chloride entry is not the cause of this undershoot after an action potential.

  • B. Slow closure of voltage-gated potassium channels (correct)

    Correct. Slowly closing potassium channels let potassium continue to leave.

  • C. Persistent opening of sodium channels

    Persistent sodium opening would depolarise the membrane, not hyperpolarise it.

  • D. Failure of the sodium-potassium pump

    Pump failure would gradually depolarise the cell, not cause a brief undershoot.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Slow closure of voltage-gated potassium channels. Voltage-gated potassium channels open with a delay and close slowly after the action potential, so potassium efflux continues briefly and drives the membrane closer to the potassium equilibrium potential, producing the after-hyperpolarisation.

Why is "Entry of chloride through ligand-gated channels" not the answer?

Chloride entry is not the cause of this undershoot after an action potential.

Why is "Persistent opening of sodium channels" not the answer?

Persistent sodium opening would depolarise the membrane, not hyperpolarise it.

Why is "Failure of the sodium-potassium pump" not the answer?

Pump failure would gradually depolarise the cell, not cause a brief undershoot.

What concept does this question test?

It tests Nerve and muscle: after-hyperpolarisation in Physiology. The relative refractory period partly reflects this.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Nerve and muscle: after-hyperpolarisation?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.