Several hours after death, skeletal muscles throughout the body become stiff and locked in position. Which molecular event is directly responsible for this state?

• A Persistent calcium release from the sarcoplasmic reticulum due to membrane breakdown
• B Progressive shortening of titin filaments within the sarcomere
• C Continued acetylcholine release from degenerating nerve terminals
• D Depletion of ATP, preventing detachment of myosin heads from actin ✓

Explanation

Cross-bridge detachment requires ATP binding to myosin. After death, ATP production ceases and stored ATP is consumed within hours, so myosin heads remain attached to actin and the muscle locks in rigor. Calcium does leak out as membranes degrade, but the stiffness itself is the absence of ATP-driven detachment, not the calcium release. Nerve terminals are inactive after death, so acetylcholine release cannot sustain the state.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.