Cardiac physiology: pacemaker potential: 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 · Cardiac physiology: pacemaker potential

Sample item

Which ionic current contributes importantly to spontaneous phase-4 depolarisation in sinoatrial nodal cells?

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

The answer and the reasoning

A. Funny sodium current

SA nodal cells gradually depolarise through the hyperpolarisation-activated funny current, calcium currents and declining potassium efflux. Their phase 0 uses calcium channels rather than fast sodium channels.

Option by option

  • A. Funny sodium current (correct)

    Correct. If current helps create automaticity in pacemaker cells.

  • B. Fast sodium current through Nav1.5

    Fast sodium channels create the rapid upstroke in working myocardium.

  • C. Inward rectifier potassium current

    Inward rectifier potassium current stabilises resting potential in working myocytes.

  • D. Chloride current

    Chloride current is not the primary pacemaker mechanism.

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 A, Funny sodium current. SA nodal cells gradually depolarise through the hyperpolarisation-activated funny current, calcium currents and declining potassium efflux.

Why is "Fast sodium current through Nav1.5" not the answer?

Fast sodium channels create the rapid upstroke in working myocardium.

Why is "Inward rectifier potassium current" not the answer?

Inward rectifier potassium current stabilises resting potential in working myocytes.

Why is "Chloride current" not the answer?

Chloride current is not the primary pacemaker mechanism.

What concept does this question test?

It tests Cardiac physiology: pacemaker potential in Physiology. Their phase 0 uses calcium channels rather than fast sodium channels.

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 Cardiac physiology: pacemaker potential?

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.