Muscle physiology: excitation-contraction coupling: 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: excitation-contraction coupling

Sample item

In skeletal muscle, calcium binds to which protein to initiate contraction?

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

The answer and the reasoning

D. Troponin C

Calcium binding to troponin C shifts tropomyosin away from actin binding sites, allowing actin-myosin cross-bridge cycling. ATP is required for both contraction cycling and relaxation.

Option by option

  • A. Tropomyosin

    Tropomyosin blocks actin sites at rest but does not bind calcium directly.

  • B. Myosin light-chain kinase

    Myosin light-chain kinase is central in smooth muscle.

  • C. Dystrophin

    Dystrophin stabilizes muscle membrane.

  • D. Troponin C (correct)

    Correct. Troponin C is the calcium sensor in skeletal muscle.

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, Troponin C. Calcium binding to troponin C shifts tropomyosin away from actin binding sites, allowing actin-myosin cross-bridge cycling.

Why is "Tropomyosin" not the answer?

Tropomyosin blocks actin sites at rest but does not bind calcium directly.

Why is "Myosin light-chain kinase" not the answer?

Myosin light-chain kinase is central in smooth muscle.

Why is "Dystrophin" not the answer?

Dystrophin stabilizes muscle membrane.

What concept does this question test?

It tests Muscle physiology: excitation-contraction coupling in Physiology. ATP is required for both contraction cycling and relaxation.

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: excitation-contraction coupling?

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.