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 event allows myosin to bind actin in skeletal muscle contraction?

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

The answer and the reasoning

C. Calcium binds troponin and shifts tropomyosin

Calcium released from the sarcoplasmic reticulum binds troponin C, moving tropomyosin away from actin's myosin-binding sites and permitting cross-bridge cycling as long as ATP is available.

Option by option

  • A. ATP permanently detaches all myosin

    ATP is needed for cycling and detachment, not permanent absence of binding.

  • B. Potassium enters the sarcoplasm

    Potassium movement is important electrically but does not expose actin sites.

  • C. Calcium binds troponin and shifts tropomyosin (correct)

    Correct: calcium-troponin binding exposes actin sites for myosin.

  • D. Sodium leaves the muscle cell

    Sodium leaving is not the trigger for cross-bridge formation.

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 C, Calcium binds troponin and shifts tropomyosin. Calcium released from the sarcoplasmic reticulum binds troponin C, moving tropomyosin away from actin's myosin-binding sites and permitting cross-bridge cycling as long as ATP is available.

Why is "ATP permanently detaches all myosin" not the answer?

ATP is needed for cycling and detachment, not permanent absence of binding.

Why is "Potassium enters the sarcoplasm" not the answer?

Potassium movement is important electrically but does not expose actin sites.

Why is "Sodium leaves the muscle cell" not the answer?

Sodium leaving is not the trigger for cross-bridge formation.

What concept does this question test?

It tests Muscle physiology in Physiology. The correct option holds because: Correct: calcium-troponin binding exposes actin sites for myosin.

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.