Rigor mortis (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

: ''rigor'' "stiffness", and ''mortis'' "of death"), or postmortem rigidity, is the third stage of death. It is one of the recognizable

signs of death Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...

, characterized by stiffening of the limbs of the

corpse A cadaver or corpse is a dead human body that is used by medical students, physicians and other scientists to study anatomy, identify disease sites, determine causes of death, and provide tissue to repair a defect in a living human being. Stud ...

caused by chemical changes in the muscles postmortem (mainly calcium).Saladin, K. S. 2010. ''Anatomy & Physiology'': 6th edition. McGraw-Hill. In humans, rigor mortis can occur as soon as four hours after death. Contrary to folklore and common belief, rigor mortis is not permanent and begins to pass within hours of onset. Typically, it lasts no longer than eight hours at "room temperature".

Physiology

After death, aerobic respiration in an organism ceases, depleting the source of oxygen used in the making of

adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms ...

(ATP). ATP is required to cause separation of the actin-myosin cross-bridges during relaxation of muscle.Hall, John E., and Arthur C. Guyton. Guyton and Hall Textbook of Medical Physiology. Philadelphia, PA: Saunders/Elsevier, 2011. MD Consult. Web. 26 January 2015. When oxygen is no longer present, the body may continue to produce ATP via anaerobic

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

. When the body's

glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one of ...

is depleted, the ATP concentration diminishes, and the body enters rigor mortis because it is unable to break those bridges. Calcium enters the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

after death. Calcium is released into the cytosol due to the deterioration of the

sarcoplasmic reticulum The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca2+). Calcium ion levels are ke ...

. Also, the breakdown of the sarcolemma causes additional calcium to enter the cytosol. The calcium activates the formation of actin-myosin cross-bridging. Once calcium is introduced into the cytosol, it binds to the troponin of thin filaments, which causes the troponin-tropomyosin complex to change shape and allow the myosin heads to bind to the active sites of actin proteins. In rigor mortis

myosin Myosins () are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility. The first myosin (M ...

heads continue binding with the active sites of actin proteins via

adenosine diphosphate Adenosine diphosphate (ADP), also known as adenosine pyrophosphate (APP), is an important organic compound in metabolism and is essential to the flow of energy in living cells. ADP consists of three important structural components: a sugar backbone ...

(ADP), and the muscle is unable to relax until further enzyme activity degrades the complex. Normal relaxation would occur by replacing ADP with ATP, which would destabilize the myosin-actin bond and break the cross-bridge. However, as ATP is absent, there must be a breakdown of muscle tissue by

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s (endogenous or bacterial) during

decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and ...

. 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. Decomposition of the myofilaments occurs between 48 and 60 hours after the peak of rigor mortis, which occurs approximately 13 hours after death.

Applications in meat industry

Rigor mortis is very important in the

meat industry The meat industry are the people and companies engaged in modern industrialized livestock agriculture for the production, packing, preservation and marketing of meat (in contrast to dairy products, wool, etc.). In economics, the meat industry is ...

. The onset of rigor mortis and its resolution partially determines the tenderness of

meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...

. If the post-slaughter meat is immediately chilled to 15 °C (59 °F), a phenomenon known as cold shortening occurs, whereby the muscle sarcomeres shrink to a third of their original length. Cold shortening is caused by the release of stored

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

ions from the

of muscle fibers, in response to the cold stimulus. The calcium ions trigger powerful muscle contraction aided by ATP molecules. To prevent cold shortening, a process known as electrical stimulation is carried out, especially in beef carcasses, immediately after slaughter and

skinning Skinning is the act of skin removal. The process is done by humans to animals, mainly as a means to prepare the meat beneath for cooking and consumption, or to harvest the skin for making fur clothing or tanning it to make leather. The sk ...

. In this process, the

carcass Carcass or Carcase (both pronounced ) may refer to: *Dressed carcass, the body of a livestock animal ready for butchery, after removal of skin, visceral organs, head, feet etc. *Carrion, the decaying dead body of an animal or human being *The str ...

is stimulated with

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

, causing it to contract and relax, which depletes the ATP reserve from the carcass and prevents cold shortening.

Application in forensic pathology

Postmortem interval changes (stages of death)

The degree of rigor mortis may be used in

forensic pathology Forensic pathology is pathology that focuses on determining the cause of death by examining a corpse. A post mortem examination is performed by a medical examiner or forensic pathologist, usually during the investigation of criminal law cases ...

to determine the approximate time of death. A dead body holds its position as rigor mortis sets in. If the body is moved after death, but before rigor mortis begins, forensic techniques such as livor mortis can be applied. Rigor mortis is known as

transient evidence {{Forensic science, articles Transient evidence is term used in criminal forensics to indicate elements of physical evidence that might be expected to degrade or disappear within a particular time frame. As such, it is one of the five primary ca ...

, as the degree to which it affects a body degrades over time.

Notes

References

Bibliography

* Bear, Mark F; Connors, Barry W.; Paradiso, Michael A.
''Neuroscience, Exploring the Brain''
Philadelphia : Lippincott Williams & Wilkins; Third Edition (1 February 2006). * Robert G. Mayer, "Embalming: history, theory, and practice", McGraw-Hill Professional, 2005, * "Rigor mortis and Other Postmortem Changes - Burial, Body, Life, Cause, Time, Person, Human, Putrefaction." Encyclopedia of Death and Dying. 2011. Web. 4 December 2011.

. * Saladin, Kenneth. Anatomy and Physiology: The Unity of Form and Function, 6th ed. McGraw-Hill. New York, 2012. {{Death Signs of death Latin medical words and phrases Medical aspects of death Forensic pathology

Physiology

Applications in meat industry

Application in forensic pathology

See also

Notes

References

Bibliography