Pick one of the artifacts of decomposition we have discussed thus far this semester; research and discuss – in no less than 1,500 words – the scientific research that has been conducted on the subject including landmark discoveries and advances.
3.1 Rigor mortis
Rigor mortis is defined as the stiffening of muscles that occurs after death, also sometimes known as postmortem rigidity. During this process, the body undergoes chemical changes after death which cause the muscles to stiffen soon after death (usually within a few hours) and then to once again become flaccid after the decomposition process breaks down the bonds causing the muscle stiffening. That is, the muscle fibers themselves bond together to cause postmortem stiffening or muscle contraction.
During life, muscles stiffen/contract and release due to the relationship of 4 primary chemicals: adenosine triphosphate (ATP), adenosine diphosphate (ADP), actin, and myosin. ATP causes the separation between the cross bridges between actin and myosin – effectively relaxing the muscles. In the absence of ATP, actin and myosin will bond together through ADP – effectively causing stiffening or contraction. After death, the body stops producing the oxygen necessary to produce ATP, although some may still be produced after death due to anaerobic glycolysis. However, once all of the ATP is depleted from a body, rigor mortis begins due to the bodyâ€s inability to break the actin-myosin bonds.
Because rigor mortis – through the depletion of ATP and the bonding of the actin and myosin molecules – causes a postmortem stiffening of the muscles, it is an excellent means to determine the postmortem body position of a decedent. It can also be useful for determining if a body was moved after rigor mortis began but before it fully dissipated.
3.1.1 The process of rigor mortis
The process of rigor mortis begins immediately after death as the oxygen source necessary to continue ATP production ceases. However, muscle stiffening does not generally immediately begin – though there are several notable exceptions which will be discussed in a subsequent section. For the first several hours after death in normal cases, the body remains fully relaxed in a state called primary flaccidity. While there have been various research studies with inconsistent results that discuss the process in which rigor mortis begins, progresses, and dissipates, it is generally agreed upon that rigor mortis becomes apparent first in the small muscle groups such as those of the face and upper-body extremities. Amongst these many research studies regarding the process of rigor mortis, one of the first studies on the order in which it occurs was published by a French physician in 1811. This study, authored by P.H. Nysten, stated that, “The rigidity in humans begins in the truck and neck, followed by the upper extremities and after that by the lower limbs. It follows the same order during the resolution.†This phrase soon became known as Nystenâ€s Law which is used to describe the standard progression of rigor mortis.
Rigor mortis generally begins to occur and become physically apparent within 4-6 hours after death. At approximately 12-24 hours postmortem, rigor mortis is said to reach its maximum meaning that all of the muscles in the body are in a stiffened state. Then, between 24-48 hours – or longer in some cases – rigor mortis begins to dissipate in the same order in which it onset; that is, the small muscles of the face and upper-body extremities return to a flaccid state before those of the lower body. Rigor mortis dissipates as a result of the decomposition process which degrades the actin-myosin bonds and breaks them down which then releases the muscles to a flaccid state once again.
As with many artifacts of decomposition, rigor mortis is highly temperature dependent. Heat accelerates the onset and progression of rigor mortis while cold slows it down. In cases of hypothermia or significantly below freezing temperature, decomposition (and consequently rigor mortis) will all-but cease to progress. Some studies have indicated that a colder environment presents for a more rigidly fixed state of rigor mortis – that is, rigor that is harder to “break†with applied force – which is a phenomenon known as cold rigidity. The amount of muscle mass of the individual in question and their general health also factor into the progression of rigor mortis. In individuals with lower muscle mass (e.g., children or elderly individuals) rigor mortis will typically onset and progress faster than those with a higher concentration of muscle mass. Additionally, drug use has been suggested to alter the progression of rigor mortis in accordance with the nature of the drug. That is, stimulants such as amphetamines or cocaine have been shown to accelerate the onset of rigor mortis.
3.1.2 Anomalies/abnormalities with rigor mortis
While rigor mortis generally takes between 4-6 hours to become physically apparent after death, there are certain circumstances in which rigor mortis is nearly instantaneous. In cases of individuals whose bodies had already depleted their stores of ATP above the critical threshold (generally considered to be 85%), instantaneous or nearly instantaneous rigor mortis has been observed. Examples of such cases include those with seizure disorders where a seizure was associated with the death event, those who engaged in intense physical exercise around the time of death, or those who had an extremely high fever at the time of death. There is also a condition where certain muscle groups which were already in a severely contracted state at the time of death will enter into rigor mortis faster than would be considered normal. This is called a cadaveric spasm and has been observed in cases such as electrocution where the parts of the decedentâ€s body that were in contact with the source of the electrocution entered into rigor mortis much more rapidly than normal. Cadaveric spasm has also been observed in physically traumatic deaths such as a suicide by slitting oneâ€s own throat or drowning victims in which the decedents have been observed grasping the knife tightly and clutching onto plants or other materials, respectively.
There have been several published case studies that indicate certain causes of death have an effect on the process of rigor mortis. One such cause is that of strychnine poisoning which causes rigor mortis to onset more rapidly than normal conditions. Strychnine is a very potent toxin that produces significant physiological changes in humans after ingestion. Within half an hour after the initial exposure, subjects experience intense muscle spasms and convulsions which typically lead to death within 2-3 hours. Researchers have suggested that the rapid onset of rigor mortis is due to the intense muscle spasms and convulsions associated with the strychnine poisoning, similar to what may happen to individuals who die as a result of seizures. Conversely, carbon monoxide is said to delay the onset of rigor mortis, though the exact reason for this delay is not well documented in scientific literature.
In quadrupeds, rigor mortis may not always be an accurate representation of body position at the time of death. When a quadruped dies lying on its side and begins to bloat as a normal artifact of decomposition, this may – in some cases – occur prior to rigor mortis reaching its maximum phase. As a result, the rigor mortis alone might indicate that the quadrupedâ€s outer limbs were elevated at the time of death but this condition is more appropriately explained by the bloating of the torso lifting the outer limbs away from the body and then stiffening as rigor mortis sets in.
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