Rigor Mortis

What is Rigor Mortis?

Rigor Mortis or postmortem rigidity is the stiffness of the muscles and joints of the body post-death of a person, usually lasting between one to four days. It is the third stage and a noticeable sign of death which is due to chemical changes in the muscles which brings about a stiffening of the muscles of limbs.

Rigor mortis is one of the recognizable taphonomic changes which causes rigidity in the structure of muscles. The occurrence and physiology of rigor mortis are important to understanding.

Causes of Rigor Mortis

Following are the causes of Rigor Mortis explained in detail:

Chemical Changes

Chemicals changes in the muscles after death result in rigor mortis. When a person dies, the body no longer receives oxygen. As a result, chemical reactions and exchanges do not occur. The muscles cannot produce ATP. The actin and myosin filaments remain contracted and the muscles remain tense.

Temperature

The body of a person who died in a warmer climate will experience chemical changes faster than that in the colder climate. The bodies submerged in freezing water for several days do not undergo stages of rigor mortis. It only begins once the body starts to thaw.

See also: Muscle Contractions And Contractile Proteins

Occurrence of Rigor Mortis

Sliding filament theory in fibres of muscles depends upon the conversion of ATP to ADP.

Post-death, due to lack of respiratory activity in the corpse, there is a dramatic decrease in the pH level of the cells due to the synthesis of pyruvic and lactic acid.

The glycolysis of glycogen in the absence of oxygen in muscles causes glycogen exhaustion leading to fewer ATP concentrations where ATP would otherwise be used to detach the cross-linking of fibres. Hence the related rigidity would be reversed.

This rigidity is first noticed in hands targeted at smaller muscle groups which extend from a span of 4 hours, eventually approaching larger muscle classes within 12 hours post death resulting in the body getting stiffened.

It depends upon decreased levels of ATP at the time of death.

Rigor Mortis finds applications in the reconstruction of the postmortem period by maintaining the exact position of the body, displaying any efforts made to move the corpse which relies upon – rigidity of the body at the time of its discovery and the time factor.

The body reverses to a floppy state after 36-40 hours from the time of death.

During death, primary flaccidity takes place causing stiffening of the muscles of jaws, eyelids, neck.

The order of areas affected differs depending upon the lactic acid in muscles which is influenced by glycogen in muscles.

It then approaches towards internal organs which depends upon the gender, physical built and condition.

Stages of Rigor Mortis

There are four important stages of Rigor Mortis- Autolysis, Bloat, Active Decay, and Skeletonization. All these rigor mortis stages are explained in detail:

Stage I- Autolysis

This stage is also known as self-digestion and begins immediately after death. The blood circulation and respiratory activities stop soon after death. The body cannot get oxygen or remove metabolic waste. This creates an acidic environment in the body due to which the cells rupture. Small blisters start appearing on the skin and internal organs. The top layer of the skin begins to loosen. The membranes produce enzymes that eat the cells.

Stage II- Bloat

The enzymes produced by the membranes produce many gases. The colour of the skin fades due to the sulfur-containing compounds released by the bacteria. Foul odours are produced by the microorganisms in the process called putrefaction.

Stage III- Active Decay

All the body parts become liquified at this stage. All the soft tissues of the body decompose. The hair, bones, cartilages of the decay remain.

Stage IV- Skeletonization

There is no set time frame when skeletonization occurs. This is because the decomposition rate depends upon the loss of organic and inorganic components.

Applications Of Rigor Mortis Across Different Streams

Rigor mortis finds applications in various fields such as:

Meat Industry

Rigor mortis plays a major role in the meat industry as its onset and resolution are deciding factors for meat to get tender. Cold shortening occurs if the meat is chilled immediately, resulting in meat shrinkage. It is caused by stored calcium ions from muscle fibres due to cold reflexes. It can be prevented using electrical stimulation.

Forensic Science

It finds major applications in the forensic field of science as it can be used to determine the exact time of death since the body stiffens on the onset of rigor mortis process.

Livor mortis is a technique used to determine if the body has been displaced post-death before rigor mortis initiates.

Ambient temperature is one factor which affects the process of rigor mortis, where pace and onset of the process are faster in warmer conditions facilitating a favourable environment for metabolic process causing decay.

On the other hand, lower temperatures slow down the process.

This article gives a detailed account of what is rigor mortis, its stages and applications. What happens to a body after death is described in this article.

For more details on Rigor mortis and chemical changes in the human body register at BYJU’S website or download BYJU’S app for further reference.

Related Links: Glycolysis: An Introduction To Glycolytic Pathway

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