Nerve and muscle: dystrophin: 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: dystrophin

Sample item

A 5-year-old boy has difficulty rising from the floor, calf enlargement and a creatine kinase about twenty times normal. Which protein function is lost?

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

The answer and the reasoning

B. Dystrophin, which links the actin cytoskeleton to the sarcolemmal glycoprotein complex

Dystrophin connects intracellular actin to the dystroglycan complex and the extracellular matrix, stabilising the sarcolemma during contraction. Without it, membranes tear, creatine kinase leaks out and fibres are replaced by fat and connective tissue, causing pseudohypertrophy of the calves in Duchenne muscular dystrophy.

Option by option

  • A. Ryanodine receptor, which releases calcium from the sarcoplasmic reticulum

    Ryanodine receptor defects are linked to malignant hyperthermia and central core disease.

  • B. Dystrophin, which links the actin cytoskeleton to the sarcolemmal glycoprotein complex (correct)

    Correct. Loss of the dystrophin link makes the sarcolemma fragile.

  • C. Nicotinic receptor, which opens at the end plate

    Nicotinic receptor loss causes myasthenic syndromes without raised creatine kinase.

  • D. Titin, which links thick filaments to the Z disc

    Titin is a sarcomeric protein and is not the cause of Duchenne dystrophy.

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 B, Dystrophin, which links the actin cytoskeleton to the sarcolemmal glycoprotein complex. Dystrophin connects intracellular actin to the dystroglycan complex and the extracellular matrix, stabilising the sarcolemma during contraction.

Why is "Ryanodine receptor, which releases calcium from the sarcoplasmic reti…" not the answer?

Ryanodine receptor defects are linked to malignant hyperthermia and central core disease.

Why is "Nicotinic receptor, which opens at the end plate" not the answer?

Nicotinic receptor loss causes myasthenic syndromes without raised creatine kinase.

Why is "Titin, which links thick filaments to the Z disc" not the answer?

Titin is a sarcomeric protein and is not the cause of Duchenne dystrophy.

What concept does this question test?

It tests Nerve and muscle: dystrophin in Physiology. Without it, membranes tear, creatine kinase leaks out and fibres are replaced by fat and connective tissue, causing pseudohypertrophy of the calves in Duchenne muscular dystrophy.

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: dystrophin?

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.