Editing Rigor mortis (section)

== Physiology ==
[[File:People Dead 1991 in Sandwip.jpg|thumb|220px|right|Corpses of victims of the [[1991 Bangladesh cyclone]] in [[Sandwip]] displaying signs of rigor mortis]]
After death, aerobic respiration in an organism ceases, depleting the source of oxygen used in the making of [[adenosine triphosphate]] (ATP). ATP is required to cause separation of the [[Myofibril|actin-myosin]] [[Sliding filament theory|cross-bridges]] during relaxation of muscle.<ref name="auto">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.</ref> When oxygen is no longer present, the body may continue to produce ATP via anaerobic [[glycolysis]]. When the body's [[glycogen]] is depleted, the ATP concentration diminishes, and the body enters rigor mortis because it is unable to break those bridges.<ref>{{cite journal|last1=Fremery|first1=Donald|date=3 February 1959|title=Biochemistry of Chicken Muscle as Related to rigor mortis and Tenderization|journal=Journal of Food Science|volume=25|issue=1|pages=73–87|doi=10.1111/j.1365-2621.1960.tb17938.x}}</ref><ref name="Ask a Scientist">{{cite web|url=http://www.newton.dep.anl.gov/askasci/zoo00/zoo00248.htm|title=Classroom Resources - Argonne National Laboratory}}</ref>

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]] 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]] (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 (biology)|tissue]] by [[enzyme]]s (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.<ref>{{Cite web|url=http://chemistry.about.com/cs/biochemistry/a/aa0|title=About.com (archived)}}{{dead link|date=June 2020|bot=medic}}{{cbignore|bot=medic}}</ref>

Decomposition of the myofilaments occurs between 48 and 60 hours after the peak of rigor mortis, which occurs approximately 13 hours after death.<ref name="saladin" />
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