Thanatology: mechanism of rigor mortis: practice question

A Forensic Medicine 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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Forensic Medicine · Thanatology: mechanism of rigor mortis

Sample item

A forensic student asks why muscles stiffen a few hours after death. Which biochemical event is mainly responsible for rigor mortis?

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

The answer and the reasoning

D. Depletion of ATP, so myosin heads cannot detach from actin

After death, anaerobic glycolysis falls and ATP is depleted. ATP is needed to break the actin-myosin cross-bridges, so the filaments stay locked and the muscle becomes rigid. Rigor later passes off when putrefaction breaks down the muscle proteins.

Option by option

  • A. Loss of calcium from the muscle, preventing any contraction

    Calcium release initiates cross-bridge binding and does not prevent it.

  • B. Excess ATP that keeps myosin locked on actin

    ATP is lacking, not in excess; ATP actually relaxes the muscle.

  • C. Coagulation of myosin by acidification alone

    Lactic acid contributes to muscle changes, but the stiffness itself depends on ATP loss rather than protein coagulation.

  • D. Depletion of ATP, so myosin heads cannot detach from actin (correct)

    Correct. Without ATP the cross-bridges cannot be released, so the muscle remains stiff.

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.

More Forensic Medicine questions

Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is D, Depletion of ATP, so myosin heads cannot detach from actin. After death, anaerobic glycolysis falls and ATP is depleted.

Why is "Loss of calcium from the muscle, preventing any contraction" not the answer?

Calcium release initiates cross-bridge binding and does not prevent it.

Why is "Excess ATP that keeps myosin locked on actin" not the answer?

ATP is lacking, not in excess; ATP actually relaxes the muscle.

Why is "Coagulation of myosin by acidification alone" not the answer?

Lactic acid contributes to muscle changes, but the stiffness itself depends on ATP loss rather than protein coagulation.

What concept does this question test?

It tests Thanatology: mechanism of rigor mortis in Forensic Medicine. ATP is needed to break the actin-myosin cross-bridges, so the filaments stay locked and the muscle becomes rigid. Rigor later passes off when putrefaction breaks down the muscle proteins.

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 Thanatology: mechanism of rigor mortis?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.