Rigor mortis is one of the recognizable signs of death, caused by chemical changes in the
muscles after death, causing the limbs of the corpse to become stiff and difficult to
move or manipulate.
In humans, it commences after about three to four hours, reaches maximum stiffness after
12 hours, and gradually dissipates from approximately 24 hours after death.
Biochemistry After death, ventilation in organisms ceases
to occur, depleting the corpse of oxygen used in the making of adenosine triphosphate.
ATP is no longer provided to operate the SERCA pumps in the membrane of the sarcoplasmic
reticulum, which pump calcium ions into the terminal cisternae.
This prevents calcium ions from leaving the muscle fibre and hence calcium ions keep on
binding with troponin causing the cross-bridge to remain between myosin heads and actin proteins.
Also, as there is an unavailability of ATP, the myosin heads keep on binding with the
active sites of actin proteins and the muscle is unable to relax until further enzyme activity.
Unlike in normal muscular contraction, after death, the body is unable to complete the
cycle and release the coupling between the myosin and actin, creating a state of muscular
contraction until the breakdown of muscle tissue by enzymes 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.
Physical changes At the time of death, a condition called "primary
flaccidity" occurs.
Following this, the muscles stiffen in rigor mortis.
All muscles in the body are affected.
Starting between two to six hours following death, rigor mortis begins with the eyelids,
neck, and jaw.
The sequence may be due to different lactic acid levels among different muscles, which
is directly related to the difference in glycogen levels and different types of muscle fibers.
Rigor mortis then spreads to the other muscles within the next four to six hours, including
the internal organs.
The onset of rigor mortis is affected by the individual's age, sex, physical condition,
and muscular build.
Rigor mortis may not be perceivable in many infant and child corpses due to their smaller
muscle mass.
Applications in meat industry Rigor mortis is very important in meat technology.
The onset of rigor mortis and its resolution partially determines the tenderness of meat.
If the postslaughter meat is immediately chilled to 15°C, a phenomenon known as cold shortening
occurs, where 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, 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 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.
If the position in which a body is found does not match the location where it is found,
that could mean someone moved it.
Several factors also affect the progression of rigor mortis, and investigators take these
into account when estimating the time of death.
One such factor is the ambient temperature.
When conditions are warm, the onset and pace of rigor mortis are sped up by providing a
conducive environment for the metabolic processes that cause decay.
Low temperatures, however, slow them down.
Therefore, for a person who dies outside in frozen conditions rigor mortis may last several
days more than normal, so investigators may have to abandon it as a tool for determining
time of death.
See also Cadaveric spasm
References
Bibliography Bear, Mark F; Connors, Barry W.; Paradiso,
Michael A., Neuroscience, Exploring the Brain, Philadelphia : Lippincott Williams & Wilkins;
Third Edition.
ISBN 0-7817-6003-8 Robert G. Mayer, "Embalming: history, theory,
and practice", McGraw-Hill Professional, 2005, ISBN 0-07-143950-1
"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.
Peress, Robin.
"Discovery Health "Rigor Mortis at the Crime Scene"" Discovery Health "Health Guides" Discovery
Fit & Health, 2011.
Web.
4 December 2011.
.