Histology: skeletal muscle sarcomere: practice question

A Anatomy 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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Anatomy · Histology: skeletal muscle sarcomere

Sample item

On electron microscopy of a skeletal muscle fibre during contraction, the thin filaments slide between the thick filaments. Which band stays the same length during this contraction?

AZ line to Z line distanceBH zoneCI bandDA band

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

The answer and the reasoning

D. A band

The A band corresponds to the length of the thick myosin filaments, which does not change during sliding. The I band (thin filaments only) and the H zone (thick filaments only) both narrow, and the sarcomere, measured Z line to Z line, shortens. This is the sliding filament model.

Option by option

A. Z line to Z line distance
The Z to Z distance is the sarcomere length, which shortens with contraction.
B. H zone
The H zone narrows and may vanish as thin filaments meet in the centre.
C. I band
The I band narrows as thin filaments move into the A band.
D. A band (correct)
Correct. The A band is the thick filament length and remains constant.

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.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is D, A band. The A band corresponds to the length of the thick myosin filaments, which does not change during sliding.

Why is "Z line to Z line distance" not the answer?

The Z to Z distance is the sarcomere length, which shortens with contraction.

Why is "H zone" not the answer?

The H zone narrows and may vanish as thin filaments meet in the centre.

Why is "I band" not the answer?

The I band narrows as thin filaments move into the A band.

What concept does this question test?

It tests Histology: skeletal muscle sarcomere in Anatomy. The I band (thin filaments only) and the H zone (thick filaments only) both narrow, and the sarcomere, measured Z line to Z line, shortens. This is the sliding filament model.

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 Histology: skeletal muscle sarcomere?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.