Rigor mortis is a condition at death in which

Rigor mortis is a condition at death in which

• A. A temporary rise in body temperature after death
• B. An increase in ATP causing muscle relaxation
• C. A condition at death in which a lack of ATP leads to no breakage of actin-myosin cross bridges leading to muscle stiffness
• D. Rapid consumption of sugars by muscles after death

Answer: (C)

Rigor mortis happens because, after death, cellular respiration stops and ATP is no longer produced. Without ATP, the myosin heads remain bound to actin after they’ve formed cross-bridges, so the muscle fibers cannot detach and relaxation cannot occur. This makes muscles stiff over several hours, with stiffness peaking and then fading as proteins break down during decomposition. The other options don’t fit because none describe the need for ATP to detach cross-bridges; postmortem bodies don’t experience a rise in temperature, ATP levels don’t increase, and while metabolism of stored sugars may occur briefly, it’s the ATP depletion that drives the stiffness.

Rigor mortis happens because, after death, cellular respiration stops and ATP is no longer produced. Without ATP, the myosin heads remain bound to actin after they’ve formed cross-bridges, so the muscle fibers cannot detach and relaxation cannot occur. This makes muscles stiff over several hours, with stiffness peaking and then fading as proteins break down during decomposition. The other options don’t fit because none describe the need for ATP to detach cross-bridges; postmortem bodies don’t experience a rise in temperature, ATP levels don’t increase, and while metabolism of stored sugars may occur briefly, it’s the ATP depletion that drives the stiffness.