A forensic pathologist notes progressive stiffening of the jaw and limb muscles in a body several hours after death. Which molecular event underlies this rigidity?

• A Sustained elevation of cytosolic calcium due to membrane leak, with ATP depletion preventing cross-bridge detachment ✓
• B Progressive shortening of the titin springs after proteolytic degradation
• C Continued acetylcholine release from degenerating nerve terminals
• D Calcium influx through dihydropyridine receptors that remain open without ATP

Explanation

Rigor mortis occurs because ATP is required for myosin to detach from actin. After death, ATP synthesis stops while membrane breakdown raises cytosolic calcium, allowing persistent cross-bridge formation that cannot detach, fixing the muscle in a rigid state. Nerve activity is irrelevant because transmitter release also ceases without ATP, which eliminates option C. The stiffness later resolves as proteolysis destroys the contractile apparatus.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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