點解人死了一段時間會變硬？

Rigor mortis is one of the recognisable signs of death (Latin "mors, mortis") that is caused by a chemical change in the muscles after death, causing the limbs of the corpse to become stiff (Latin "rigor") and difficult to move or manipulate. Assuming mild temperatures, rigor usually sets in about 3-4 hours after clinical death, with full rigor being in effect at about 12 hours, and eventually subsiding to relaxation at about 36 hours. Times for the onset of rigor mortis can vary from a few minutes to several hours depending on the temperature of the environment in which the body is found.

The biochemical cause of rigor mortis is hydrolysis of ATP in the muscle tissue, the chemical energy source required for movement. Myosin molecules devoid of ATP become permanently adherent to actin filaments to form actomyosin complex, causing muscles to become rigid. After the pH of the muscle has become 5.5, release of autolytic enzymes stored in lysosomes will take place. The major proteolytic enzymes are Cathepsins and Calpains. These enzymes act at the myofibrillar proteins and hydrolyse them. As a result, the actomyosin complex is broken down and muscles become "soft" again. This is known as resolution of rigor.

2006-11-23 01:35:11 補充：
屍彊(rigor mortis):人死後因肌肉中ATP消耗, 蛋白質actin和myosin會永久連結, 肌肉變得彊硬.隨時間過去(因溫度而異), 蛋白酶釋出, 分解actin和myosin, 肌肉因此轉為柔軟.

2006-11-23 10:15:55 補充：
sorry打錯字, 應該是~屍僵~僵硬的僵