Question

Your roommate, who is a theatre major, is really into murders. They really like watching crime shows and following the news about high-profile deaths. Right now, because of a show they saw, they’re curious about how people use the state of a dead body to figure out how long ago a death occurred. They share that one thing that usually happens after death is called rigor mortis, where the muscles get really stiff. They ask you, “Why does that happen?” You are going out of town for a few days, but you’ll promise you’ll send them a message soon.

To help yourself understand, write a summary of at least >150 words to yourself about how rigor mortis occurs. Use your own words but incorporate scientific terminology and reasoning. Try to get as molecular as possible!

Answer 1

• Rigor mortis (also called rigor) come from Latin term (Rigor meaning ‘stiffness’, mortis meaning ‘of death’), reflects post mortem stiffness of muscles, resulting due to several biochemical changes in the body.
• Rigor mortis is considered as the third stage of death and is indicative sign of death. It may initiate on average of 4 to six hours after death, and the effect may remain some hors to even days (12 to 84 hours), depending upon the physiological state of the body.
• With the initial signs of death, especially cardiac arrest and respiratory arrest, there are chains of biochemical activities leading to muscle rigidity or onset of rigor mortis, initiating first in smaller muscles of face, moving towards larger muscles.
• Actin and myosin together form the contractile elements of muscle.
• Contraction of muscles calcium and energy in form of ATP.
• When there is arrest of heart and respiratory system, aerobic respiratory cycles cannot generate ATP. Initially, (before onset of rigor mortis), some amount of ATP may be generated anaerobically.
• But soon re-synthesis of ATP is inhibited.
• Due to lack of ATP, there is leaking of calcium from muscle cells. The myosin-actin units of muscles are unable to regain a relax state. As a result, the muscle fibers of the body contracts and there is onset of rigor mortis.
• The rate of onset of rigor mortis is affected by the amount of glycogen present in muscles (for ATP generation), temperature and pH of muscle.

After a period of rigor mortis state, the muscle s again regains a flaccid or relax state. This is because, the proteolytic enzymes of the body, start degradation of actin-myosin fibers of muscles. Finally, due to degraded muscle fibers, the contracted state of muscle becomes less and finally the muscles become flaccid again, after the commencement of rigor mortis stage.