Nerve and muscle: hypokalaemic weakness: 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.

Try it

Physiology · Nerve and muscle: hypokalaemic weakness

Sample item

A patient on a potent diuretic has serum potassium of 2.4 mmol/L and generalised muscle weakness. Why does a low extracellular potassium cause weakness?

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

The answer and the reasoning

C. The membrane hyperpolarises, moving the resting potential further from threshold

Lowering extracellular potassium makes the potassium equilibrium potential more negative, so the resting potential hyperpolarises. A larger depolarisation is then needed to reach threshold, reducing excitability and causing weakness. Hyperkalaemia, in contrast, causes weakness through depolarisation and sodium channel inactivation.

Option by option

  • A. Calcium release from the sarcoplasmic reticulum is blocked

    Sarcoplasmic reticulum calcium release is not the primary problem.

  • B. Acetylcholine release from the nerve terminal is abolished

    Acetylcholine release is not abolished by low potassium.

  • C. The membrane hyperpolarises, moving the resting potential further from threshold (correct)

    Correct. Hyperpolarisation increases the distance to threshold.

  • D. The membrane depolarises, causing sodium channel inactivation

    Depolarisation with sodium channel inactivation is the mechanism in hyperkalaemia.

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.

More Physiology questions

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, The membrane hyperpolarises, moving the resting potential further from threshold. Lowering extracellular potassium makes the potassium equilibrium potential more negative, so the resting potential hyperpolarises.

Why is "Calcium release from the sarcoplasmic reticulum is blocked" not the answer?

Sarcoplasmic reticulum calcium release is not the primary problem.

Why is "Acetylcholine release from the nerve terminal is abolished" not the answer?

Acetylcholine release is not abolished by low potassium.

Why is "The membrane depolarises, causing sodium channel inactivation" not the answer?

Depolarisation with sodium channel inactivation is the mechanism in hyperkalaemia.

What concept does this question test?

It tests Nerve and muscle: hypokalaemic weakness in Physiology. A larger depolarisation is then needed to reach threshold, reducing excitability and causing weakness. Hyperkalaemia, in contrast, causes weakness through depolarisation and sodium channel inactivation.

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: hypokalaemic weakness?

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.