Muscle physiology: muscle spindle dynamic response: 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: muscle spindle dynamic response

Sample item

A reflex hammer strikes the patellar tendon, causing a brief rapid stretch of the quadriceps. Which receptor generates the largest burst of discharge during the changing phase of the stretch?

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

The answer and the reasoning

C. Primary (Ia) endings on nuclear bag fibres of the muscle spindle

Primary endings, especially on dynamic nuclear bag fibres, are sensitive to the rate of change of length and so produce a large burst during a tap. Secondary endings on nuclear chain fibres mainly signal sustained (static) length. Golgi tendon organs respond to tension.

Option by option

  • A. Golgi tendon organs and their Ib afferents

    Golgi tendon organs are in series with muscle and monitor tension, not stretch velocity.

  • B. Secondary (II) endings on nuclear chain fibres

    Secondary endings are mainly static length detectors with little velocity sensitivity.

  • C. Primary (Ia) endings on nuclear bag fibres of the muscle spindle (correct)

    Correct. Ia endings signal both velocity and length, with strong velocity sensitivity.

  • D. Free nerve endings in the muscle connective tissue

    Free nerve endings are nociceptors and do not generate the stretch reflex.

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 C, Primary (Ia) endings on nuclear bag fibres of the muscle spindle. Primary endings, especially on dynamic nuclear bag fibres, are sensitive to the rate of change of length and so produce a large burst during a tap.

Why is "Golgi tendon organs and their Ib afferents" not the answer?

Golgi tendon organs are in series with muscle and monitor tension, not stretch velocity.

Why is "Secondary (II) endings on nuclear chain fibres" not the answer?

Secondary endings are mainly static length detectors with little velocity sensitivity.

Why is "Free nerve endings in the muscle connective tissue" not the answer?

Free nerve endings are nociceptors and do not generate the stretch reflex.

What concept does this question test?

It tests Muscle physiology: muscle spindle dynamic response in Physiology. Secondary endings on nuclear chain fibres mainly signal sustained (static) length. Golgi tendon organs respond to tension.

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: muscle spindle dynamic response?

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.