Summary
Highlights
After death, the body can no longer control calcium distribution. Calcium ions, due to passive diffusion, spread throughout muscle fibers. This influx of calcium triggers muscle contraction, as calcium is essential for myosin heads to bind to actin and initiate the power stroke.
Rigor mortis, meaning 'stiff death,' describes the stiffening of muscles that occurs after an organism dies. This phenomenon is a direct result of changes in calcium concentration and ATP supply within muscle cells.
Initially after death, some ATP is still available, allowing myosin heads to repeatedly grab and release actin, causing some residual muscle movement. However, a constant supply of ATP is required not only for muscle contraction but also for the dissociation of myosin from actin (breaking of cross-bridges). Without new ATP production, myosin heads remain attached to actin, leading to the sustained contraction and stiffness characteristic of rigor mortis.
Rigor mortis typically sets in about 3-4 hours after death, once ATP has completely depleted. Muscles reach their stiffest state around 12 hours post-mortem. The effects of rigor mortis eventually wear off as the muscle proteins, including myosin, begin to degrade due to the action of microorganisms, causing the muscles to relax again. This process can be influenced by environmental factors such as temperature.
Understanding the stages of rigor mortis can be a crucial factor in forensic investigations to help determine the time of death.