äkkijäykkyys

Äkkijäykkyys, often translated as rigor mortis, is a temporary stiffening of the muscles that occurs after death. It begins within a few hours of death and typically peaks around 12 to 48 hours. This stiffening is caused by chemical changes in the muscle fibers. Following death, the body's cells no longer have a supply of oxygen and energy-producing compounds. This leads to a buildup of lactic acid, which lowers the pH of the muscle cells. Simultaneously, the sarcoplasmic reticulum releases calcium ions, which are essential for muscle contraction. In the absence of ATP, the molecule that normally allows muscles to relax, the actin and myosin filaments in the muscle fibers remain locked in a contracted state.

The onset and duration of rigor mortis can be influenced by several factors, including ambient temperature, the individual's physical condition prior to death, and the cause of death. Higher temperatures tend to accelerate the process, while colder temperatures slow it down. Rigor mortis starts in the smaller muscles, such as those in the face and neck, and then spreads to the larger muscles of the limbs and trunk. Eventually, the stiffening subsides as the muscle proteins begin to break down. This breakdown process, known as autolysis, typically starts after about 48 hours and results in the muscles becoming flaccid again. Rigor mortis is a predictable postmortem change and is often used by forensic scientists to help estimate the time of death.