Rigor mortis
Rigor mortis is one of the recognizable signs of death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

 that is caused by a chemical change in the muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

s after death, causing the limbs of the corpse to become stiff and difficult to move or manipulate. In humans it commences after about 3 hours, reaches maximum stiffness after 12 hours, and gradually dissipates until approximately 72 hours (3 days) after death. Heat sources such as fire can speed up the process of rigor mortis.


After death, cellular respiration in organisms ceases to occur, depleting the corpse of oxygen used in the making of Adenosine triphosphate
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

 (ATP). ATP is no longer provided to operate the SERCA
SERCA, or sarco/endoplasmic reticulum Ca2+-ATPase, or SR Ca2+-ATPase, is a calcium ATPase-type P-ATPase.-Function:SERCA resides in the sarcoplasmic reticulum within muscle cells...

 pumps in the membrane of the sarcoplasmic reticulum, which pump calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s into the terminal cisternae
Terminal cisternae
Terminal cisternae are enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules. These discrete regions within the muscle cell store calcium and release it when an action potential courses down the transverse tubules, eliciting muscle contraction...

. This causes calcium ions to diffuse
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 from the area of higher concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...

 (in the terminal cisternae and extracellular fluid
Extracellular fluid
Extracellular fluid usually denotes all body fluid outside of cells. The remainder is called intracellular fluid.In some animals, including mammals, the extracellular fluid can be divided into two major subcompartments, interstitial fluid and blood plasma...

) to an area of lower concentration (in the sarcomere
A sarcomere is the basic unit of a muscle. Muscles are composed of tubular muscle cells . Muscle cells are composed of tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands...

), binding with troponin
400px|thumb|right|alt = Colored dice with checkered background|Ribbon representation of the human cardiac troponin core complex in the calcium-saturated form...

 and allowing for crossbridging to occur between myosin
Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...

 and actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...


Unlike in a normal muscle contraction, after death the body is unable to complete the cycle and release the coupling
A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.The...

 between the myosin and actin, creating a perpetual state of muscular contraction, until the breakdown of muscle tissue
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

 by digestive
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

 enzymes during decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...

. As part of the process of decomposition, the myosin heads are eaten off by bacteria, allowing the muscle contraction to release and the body to relax.

Applications in industry

Rigor mortis is very important in meat technology. The onset of rigor mortis and its resolution partially determines the tenderness of meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...

. If the post-slaughter meat is immediately chilled to 15°C (59°F), a phenomenon known as cold shortening occurs, where the muscle shrinks to a third of its original size. This will lead to the loss of water from the meat along with many of the vitamins, minerals, and water soluble proteins. The loss of water makes the meat hard and interferes with the manufacturing of several meat products like cutlet
Cutlet refers to:# a thin slice of meat from the leg or ribs of veal, pork, or mutton # a fried cutlet# a croquette made of minced meat...

 and sausage
A sausage is a food usually made from ground meat , mixed with salt, herbs, and other spices, although vegetarian sausages are available. The word sausage is derived from Old French saussiche, from the Latin word salsus, meaning salted.Typically, a sausage is formed in a casing traditionally made...


Cold shortening is caused by the release of stored calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 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
Skinning, a gerund from the verb to skin, commonly refers to the act of skin removal.The process is usually done with animals, mainly as preparation of the meat beneath and/or use for the fur...

. In this process, the carcass
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...

 is stimulated with alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

, 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
Forensic pathology is a branch of pathology concerned with determining the cause of death by examination of a corpse. The autopsy is performed by the pathologist at the request of a coroner or medical examiner usually during the investigation of criminal law cases and civil law cases in some...

to determine the approximate time of death.
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