Rigor mortis (), or postmortem rigidity, is the fourth stage of death. It is one of the recognizable signs of death, characterized by stiffening of the limbs of the corpse caused by chemical changes in the

muscles Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

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 a nucleoside triphosphate that provides energy to drive and support many processes in living cell (biology), cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known ...

(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. 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. It is the main storage form of glucose in the human body. Glycogen functions as one of three regularly used forms ...

is depleted, the ATP concentration diminishes, and the body enters rigor mortis because it is unable to break those bridges. Calcium enters the cytosol after death. Calcium is released into the cytosol due to the deterioration of the sarcoplasmic reticulum. Also, the breakdown of the

sarcolemma The sarcolemma (''sarco'' (from ''sarx'') from Greek; flesh, and ''lemma'' from Greek; sheath), also called the myolemma, is the cell membrane surrounding a skeletal muscle fibre or a cardiomyocyte. It consists of a lipid bilayer and a thin ...

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 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 backbon ...

(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 An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s (endogenous or bacterial) during

decomposition Decomposition 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 is ess ...

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

meat Meat is animal Tissue (biology), tissue, often muscle, that is eaten as food. Humans have hunted and farmed other animals for meat since prehistory. The Neolithic Revolution allowed the domestication of vertebrates, including chickens, sheep, ...

. 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 ions from the sarcoplasmic reticulum 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. In this process, the carcass is stimulated with

alternating current Alternating current (AC) is an electric current that 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 w ...

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

Application in forensic pathology

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, 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 Forensic pathology

Physiology

Applications in meat industry

Application in forensic pathology

See also

Notes

References

Bibliography