Muscle physiology: 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 · Muscle physiology

Sample item

What ion binds troponin to initiate skeletal contraction?

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

The answer and the reasoning

D. Calcium

Calcium binds troponin C, shifting tropomyosin away from actin binding sites and enabling actin-myosin cross-bridge formation.

Option by option

  • A. Chloride

    Chloride does not expose actin binding sites.

  • B. Sodium

    Sodium initiates action potentials but does not bind troponin.

  • C. Magnesium

    Magnesium supports ATP handling but is not the trigger ion.

  • D. Calcium (correct)

    Correct: calcium binding to troponin initiates contraction.

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 D, Calcium. Calcium binds troponin C, shifting tropomyosin away from actin binding sites and enabling actin-myosin cross-bridge formation.

Why is "Chloride" not the answer?

Chloride does not expose actin binding sites.

Why is "Sodium" not the answer?

Sodium initiates action potentials but does not bind troponin.

Why is "Magnesium" not the answer?

Magnesium supports ATP handling but is not the trigger ion.

What concept does this question test?

It tests Muscle physiology in Physiology. The correct option holds because: Correct: calcium binding to troponin initiates contraction.

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 Muscle physiology?

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.