Raheema Javed
Last Activity: 10 Years ago
The correct answer is (2) rigor mortis.
Rigor mortis (Latin: rigor "stiffness", mortis "of death") is one of the recognizable signs of death, caused by chemical changes in the muscles after death, causing the limbs of the corpse to become stiff and difficult to move or manipulate. In humans, it commences after about three to four hours, reaches maximum stiffness after 12 hours, and gradually dissipates from approximately 24 hours after death.
After death, ventilation in organisms ceases to occur, depleting the corpse of oxygen used in the making of adenosine triphosphate (ATP). ATP is no longer provided to operate the SERCA pumps in the membrane of the sarcoplasmic reticulum, which pump calcium ions into the terminal cisternae. This prevents calcium ions from leaving the muscle fibre and hence calcium ions keep on binding with troponin causing the cross-bridge to remain between myosin heads and actin proteins. Also, as there is an unavailability of ATP, the myosin heads continue binding with the active sites of actin proteins and the muscle is unable to relax until further enzyme activity.
Unlike in normal muscular contraction, after death, the body is unable to complete the cycle and release the coupling between the myosin and actin, creating a state of muscular contraction until the breakdown of muscle tissue by enzymes (endogenous or bacterial) during decomposition. As part of the process of decomposition, the myosin heads are degraded by the enzymes, allowing the muscle contraction to release and the body to relax.
At the time of death, a condition called "primary flaccidity" occurs. Following this, the muscles stiffen in rigor mortis. All muscles in the body are affected. Starting between two to six hours following death, rigor mortis begins with the eyelids, neck, and jaw. The sequence may be due to different lactic acid levels among different muscles, which is directly related to the difference in glycogen levels and different types of muscle fibers. Rigor mortis then spreads to the other muscles within the next four to six hours, including the internal organs. The onset of rigor mortis is affected by the individual's age, sex, physical condition, and muscular build. Rigor mortis may not be perceivable in many infant and child corpses due to their smaller muscle mass
