Neuromuscular junction: Lambert-Eaton syndrome: 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 · Neuromuscular junction: Lambert-Eaton syndrome

Sample item

A 62-year-old heavy smoker has proximal leg weakness, dry mouth and absent knee jerks. Strength and reflexes improve briefly after a 10-second maximal voluntary contraction, and high-frequency nerve stimulation shows a marked increase in the muscle response. Which mechanism explains the improvement?

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

The answer and the reasoning

A. Calcium accumulation in the motor nerve terminal during repetitive firing increases acetylcholine release

In Lambert-Eaton syndrome, antibodies against presynaptic P/Q-type calcium channels reduce calcium entry and so the quantal release of acetylcholine. Rapid repetitive stimulation allows residual calcium to accumulate, which facilitates release and increases the response. The association with small cell lung cancer should prompt a search for malignancy.

Option by option

  • A. Calcium accumulation in the motor nerve terminal during repetitive firing increases acetylcholine release (correct)

    Facilitation by accumulated presynaptic calcium explains the increment.

  • B. Recovery of postsynaptic receptors that were blocked by antibodies

    Postsynaptic receptor antibodies are the mechanism of myasthenia gravis, which worsens rather than improves with effort.

  • C. Reduced acetylcholinesterase activity during muscle activity

    Acetylcholinesterase activity is not altered by exercise; the defect is in transmitter release.

  • D. Increased synthesis of acetylcholine in the axon during exercise

    Acetylcholine synthesis is not the limiting step and is not increased within seconds of exercise.

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 A, Calcium accumulation in the motor nerve terminal during repetitive firing increases acetylcholine release. In Lambert-Eaton syndrome, antibodies against presynaptic P/Q-type calcium channels reduce calcium entry and so the quantal release of acetylcholine.

Why is "Recovery of postsynaptic receptors that were blocked by antibodies" not the answer?

Postsynaptic receptor antibodies are the mechanism of myasthenia gravis, which worsens rather than improves with effort.

Why is "Reduced acetylcholinesterase activity during muscle activity" not the answer?

Acetylcholinesterase activity is not altered by exercise; the defect is in transmitter release.

Why is "Increased synthesis of acetylcholine in the axon during exercise" not the answer?

Acetylcholine synthesis is not the limiting step and is not increased within seconds of exercise.

What concept does this question test?

It tests Neuromuscular junction: Lambert-Eaton syndrome in Physiology. Rapid repetitive stimulation allows residual calcium to accumulate, which facilitates release and increases the response. The association with small cell lung cancer should prompt a search for malignancy.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Neuromuscular junction: Lambert-Eaton syndrome?

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.