The loss of ATP lasting about 3 hours after death leads to which mortis phenomenon?

• A. Autolysis
• B. Rigor mortis
• C. Algor mortis
• D. Lividity

Answer: (B)

Rigor mortis is the stiffening of muscles that follows death because ATP is no longer available to power muscle relaxation. Normally, ATP lets myosin heads detach from actin after a contraction. When life ends, ATP production stops, calcium remains in the muscle, and the cross-bridges between actin and myosin stay bound. Without ATP to release them, the muscles lock into place, causing stiffness. This onset typically appears a few hours after death—around the three-hour window fits this timing—and lasts until decomposition processes begin to break down the proteins. This is different from algor mortis (cooling of the body), livor mortis (pooling of blood), and autolysis (self-digestion by enzymes).