Nerve and muscle: miniature end-plate potentials: 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 · Nerve and muscle: miniature end-plate potentials

Sample item

At a resting neuromuscular junction, a microelectrode records small spontaneous depolarisations of about 0.4 mV, each of similar size. What do these represent?

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

The answer and the reasoning

D. Release of the contents of a single acetylcholine vesicle

Miniature end-plate potentials are the postsynaptic response to spontaneous exocytosis of single vesicles, each about 5,000 to 10,000 acetylcholine molecules. They show that transmitter is released in fixed packets (quanta), and the end-plate potential is the sum of many such quanta.

Option by option

  • A. Spontaneous action potentials in the muscle fibre

    Muscle action potentials are far larger, of about 100 mV, and arise only after threshold.

  • B. Opening of voltage-gated sodium channels in the nerve terminal

    Sodium channels in the nerve terminal are not the source of a small postsynaptic potential.

  • C. Random firing of the motor neurone

    A firing motor neurone would give a full end-plate potential and not tiny uniform events.

  • D. Release of the contents of a single acetylcholine vesicle (correct)

    Correct. Each miniature potential is the effect of one vesicle (quantum).

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, Release of the contents of a single acetylcholine vesicle. Miniature end-plate potentials are the postsynaptic response to spontaneous exocytosis of single vesicles, each about 5,000 to 10,000 acetylcholine molecules.

Why is "Spontaneous action potentials in the muscle fibre" not the answer?

Muscle action potentials are far larger, of about 100 mV, and arise only after threshold.

Why is "Opening of voltage-gated sodium channels in the nerve terminal" not the answer?

Sodium channels in the nerve terminal are not the source of a small postsynaptic potential.

Why is "Random firing of the motor neurone" not the answer?

A firing motor neurone would give a full end-plate potential and not tiny uniform events.

What concept does this question test?

It tests Nerve and muscle: miniature end-plate potentials in Physiology. They show that transmitter is released in fixed packets (quanta), and the end-plate potential is the sum of many such quanta.

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 Nerve and muscle: miniature end-plate potentials?

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.