Autopsy and Gross Pathology · USMLE Step 1

Rigor mortis occurs because of which fundamental biochemical change in muscle cells after death?

  1. ATP depletion preventing actin-myosin relaxation
  2. Accumulation of lactic acid causing muscle spasm
  3. Permanent cross-linking of collagen
  4. Bacterial enzyme activity
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Correct answer: ATP depletion preventing actin-myosin relaxation

After death ATP production ceases, so actin-myosin cross-bridges cannot detach and the muscles stiffen — the basis of rigor mortis.

Difficulty: Medium Question 6 of 20

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