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"Rigidity of death" is a recognizable sign of death that is caused by a chemical change in the muscles that causes a state of rigidity (of the Latin rigor) and inflexibility in the extremities and a difficulty to move or manipulate the corpse. At a normal temperature, rigor mortis usually appears at 3-4 hours after clinical death and rigor usually has a full effect at 12 hours.
Finally, rigor mortis relaxes and yields when the muscles break down, a process that is accelerated by residual lactic acid from ATP. The term "stiff" that is given to the dead comes from this phenomenon.
When the organism dies, the sarcoplasmic reticulum membrane changes from selective to semipermeable permeability, which causes the calcium ions to leave the RS to reach equilibrium. These ions cause the troponin to change places and move to tropomyosin, which exposes the binding sites in the actin molecule, the myosin binds and effects the power stroke, but soon the ATP ends and without more glycogen to replace it the myosin molecules are unable to be released.
Rigor is generally measured in "mild", "early", "moderate" and "complete", this is totally subjective, but the perception of rigidity in an articulation corresponds to the "mild" level; the difficulty in moving a joint is an indicator of the "moderate" level; and when you have to use great force it is rigor of the "complete" level.
Phases of rigor mortis
Three phases are distinguished in the process of cadaveric rigidity (these three phases are useful to delimit with a certain approximation the date of death, according to the period of rigidity in which the corpse is found):
Establishment phase. From the start of the rigidity to its maximum intensity (3-24 hours post mortem). In this phase, rigidity can be overcome by applying a certain force, but if we stop applying it, after a certain time it is reinstated.
Status phase. It comprises since the stiffness reaches its highest intensity until just before starting to disappear (24-36 hours post mortem). In this phase the rigidity is invincible without producing tears or fractures.
Resolution phase. From 36 hours post mortem, where if the muscular rigidity is overcome by force it does not return to be restored, and after this phase the cadaverous laxity reappears.
Process of cadaverous stiffness (rigor mortis)
Initially the deceased subject has muscular atony (complete loss of strength in the muscle).
The contracture begins approximately between half an hour and 2 hours, and begins in the heart, diaphragm and smooth muscles.
Muscle relaxation phase (in smooth and striated fiber) and little by little stiffness, starting at 2 hours.
3 hours: stiff neck and upper limbs already appear
12 hours: complete rigidity
24 hours: maximum intensity. If before 24 hours we try to overcome the cadaverous rigidity, it expires, but as we reach the 24 hours it is costing us more to overcome it by gradually reinstating ourselves. From 24-36 hours the rigidity is invincible unless we break the tissues. After 36 hours the rigidity gradually disappears.
48 hours: the rigidity disappears.
Biochemical mechanism of cadaverous stiffness Edit
There are many theories but this has only been explained: When the body dies it begins to consume all the ATP that it has left: ATP ADP + H PO Thus, all the ATP is depleted, and in turn increasing the phosphoric acid that lowers the pH and causing the acidification of the medium in which the muscular contraction is established and, therefore, the cadaveric rigidity. Later, when the bacteria begin putrefaction, the medium becomes alkaline and the cadaveric rigidity disappears, resolving the contracture.
Law of Nysten's cadaverous stiffness
Nysten saw the correlation between the precocity of the contracture and its intensity and duration, so: «When the stiffness starts early it is of low intensity and limited duration; when the rigidity begins late the intensity is remarkable, and its duration, prolonged »Two groups are formed: Those who follow the law of Nysten and those who do not comply.
- They follow the Law of Nysten
Children and the elderly present early, weak and short stiffness
In athletic individuals the rigidity is later and intense and vice versa
With tiredness, the rigidity is precocious and weak
In violent deaths the rigidity is intense and lasting
In long-standing diseases, stiffness is early, weak and short
Edema hinders stiffness
Intense hemorrhages, promote early, short and weak stiffness - They do not follow the Law of Nysten
Deaths due to convulsive processes, where the rigidity is precocious, intense and lasting
Poisoning
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