Muscle physiology: excitation-contraction coupling in skeletal versus cardiac muscle: 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 · Muscle physiology: excitation-contraction coupling in skeletal versus cardiac muscle

Sample item

Strips of skeletal and ventricular muscle are placed in a calcium-free solution containing a chelator and stimulated electrically. What is observed?

AThe cardiac muscle continues to twitch while the skeletal muscle stopsBBoth muscles continue to contract normallyCThe skeletal muscle continues to twitch for a time while the cardiac muscle stops contractingDBoth muscles stop contracting at once

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

The answer and the reasoning

C. The skeletal muscle continues to twitch for a time while the cardiac muscle stops contracting

In skeletal muscle the dihydropyridine receptor acts as a voltage sensor mechanically linked to the ryanodine receptor (RyR1), so contraction does not require calcium entry. Cardiac muscle depends on calcium entering through L-type channels to trigger calcium-induced calcium release through RyR2.

Option by option

A. The cardiac muscle continues to twitch while the skeletal muscle stops
The pattern is the reverse of the real one.
B. Both muscles continue to contract normally
Cardiac muscle cannot contract normally without the trigger calcium current.
C. The skeletal muscle continues to twitch for a time while the cardiac muscle stops contracting (correct)
Correct. Skeletal muscle uses voltage-gated mechanical coupling, whereas cardiac muscle needs extracellular calcium.
D. Both muscles stop contracting at once
Skeletal muscle does not stop at once, because its coupling is independent of calcium entry.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, The skeletal muscle continues to twitch for a time while the cardiac muscle stops contracting. In skeletal muscle the dihydropyridine receptor acts as a voltage sensor mechanically linked to the ryanodine receptor (RyR1), so contraction does not require calcium entry.

Why is "The cardiac muscle continues to twitch while the skeletal muscle stops" not the answer?

The pattern is the reverse of the real one.

Why is "Both muscles continue to contract normally" not the answer?

Cardiac muscle cannot contract normally without the trigger calcium current.

Why is "Both muscles stop contracting at once" not the answer?

Skeletal muscle does not stop at once, because its coupling is independent of calcium entry.

What concept does this question test?

It tests Muscle physiology: excitation-contraction coupling in skeletal versus cardiac muscle in Physiology. Cardiac muscle depends on calcium entering through L-type channels to trigger calcium-induced calcium release through RyR2.

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 in skeletal versus cardiac muscle?

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.