Muscle physiology: summation and tetanus: 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: summation and tetanus

Sample item

When a skeletal muscle is stimulated repetitively at a high frequency, it develops a smooth sustained contraction with greater force than a single twitch. What is the main reason?

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

The answer and the reasoning

D. Sarcoplasmic calcium remains high between stimuli, so the active state is maintained

A single twitch outlasts the action potential, and the sarcoplasmic reticulum cannot take up calcium before the next stimulus arrives. Calcium therefore accumulates, the active state persists and the series elastic elements are fully stretched, so force summates up to a fused tetanus. The muscle action potential remains all-or-none and keeps its refractory period.

Option by option

  • A. Acetylcholine accumulates and keeps the end plate depolarised

    Acetylcholine is cleared rapidly by acetylcholinesterase, so it does not accumulate normally.

  • B. Each action potential becomes larger as the stimulation continues

    Action potentials remain all-or-none and do not grow with repetition.

  • C. The refractory period of the muscle membrane is abolished

    The refractory period is far shorter than the twitch, but it is not abolished.

  • D. Sarcoplasmic calcium remains high between stimuli, so the active state is maintained (correct)

    Persistently elevated calcium sustains cross-bridge cycling and allows summation.

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, Sarcoplasmic calcium remains high between stimuli, so the active state is maintained. A single twitch outlasts the action potential, and the sarcoplasmic reticulum cannot take up calcium before the next stimulus arrives.

Why is "Acetylcholine accumulates and keeps the end plate depolarised" not the answer?

Acetylcholine is cleared rapidly by acetylcholinesterase, so it does not accumulate normally.

Why is "Each action potential becomes larger as the stimulation continues" not the answer?

Action potentials remain all-or-none and do not grow with repetition.

Why is "The refractory period of the muscle membrane is abolished" not the answer?

The refractory period is far shorter than the twitch, but it is not abolished.

What concept does this question test?

It tests Muscle physiology: summation and tetanus in Physiology. Calcium therefore accumulates, the active state persists and the series elastic elements are fully stretched, so force summates up to a fused tetanus. The muscle action potential remains all-or-none and keeps its refractory period.

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: summation and tetanus?

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.