What is the postmortem stiffening of the muscles called?

• A. Rigor Mortis
• B. Livor Mortis
• C. Cadaveric Spasm
• D. Tache Noir

Answer: (A)

Rigor mortis is the postmortem stiffening of skeletal muscles due to changes inside the muscle cells after death. When life ends, the body stops producing ATP, and calcium ions accumulate in muscle cells. The myosin heads latch onto actin, and without ATP to release them, the muscles remain contracted. This causes the limbs and other muscles to become rigid. The process starts a few hours after death, often in smaller muscles first, then affects larger muscles, peaks around the first day, and gradually dissipates over the next day or two as the body's tissues break down. Temperature influences the speed of onset and duration—the warmer the environment, the faster it develops and passes.

For context, other postmortem observations aren’t about stiffening: livor mortis is the gravity-dependent coloring from blood pooling; cadaveric spasm is an instant, near-total rigidity at the moment of death; and tache noire refers to darkened lines on the eyes as the eyeballs dry.