Q. What is rigor mortis?

Dead bodies are at first limp. Many hours after death, skeletal muscles undergo a partial contraction that fixes the joints. This condition, called rigor mortis, may continue for 72 hours or more. When neurons signal living muscle fibres to contract, they do so with a neurotransmitter which is received at the surface of the muscle fiber. Signal makes the fiber open calcium ion channels and it is the calcium which causes the contraction. Muscle then removes the calcium in two ways: it stores some in its mitochondria and it pumps out the rest. When a body dies, stored calcium leaks and calcium pumps no longer function. Excess calcium causes the actin and myosin filaments of muscle fibers to remain linked, stiffening whole body until the muscles begin to decompose.