Why Rigor Mortis Occurs

Last week in my Kinesiology 173 course I learned the reason why rigor mortis sets in when a person is dead. Rigor Mortis is when all your muscles end up contracting and the body becomes stiff as a board and they become stuck like that.

To perform a contraction the myosin in your body has to bind to actin (filaments in the muscle), but there is Tropomyosin blocking the actin filaments from being binded with myosin. Calcium comes down and binds to Troponin, which unlocks Tropomyosin (protein blocking actin) sites on actin. Muscle fibers shorten when Myosin protein filaments pull together Actin protein filaments.

 The only way to break this bond is with ATP (adenosine triphosphate, which is energy). Once the myosin head is able to form a "Cross-Bridge" with the actin, it will begin a "Power Stroke". ATP is required to release the "Cross-Bridge" and prepare the myosin head for the next "Power Stroke".

When we die there is a release of calcium in the body and it starts the process of myosin binding to actin. Since there is no more energy after we die (ATP) then there is nothing to unbind the myosin from the actin so the muscles just contract and stay that way.

Image Credit: http://imgarcade.com/1/rigor-mortis-forensics/