Physiology behind Rigor Mortis

Rigor Mortis/ Postmortem Rigidity is the state of contracture that develops several hours after the death of the individual. In this condition the muscle contract and become rigid even in the absence of action potential.

The basic physiology of muscle contraction include (the numbering may not coincide with the image given below)

           In a resting muscle, Tropo-myosin covers the actin’s binding site for myosin.

2         When cytosolic calcium increases after the opening of Sarcoplasmic Ca++ channel following the        action potential, Free calcium binds with the Troponin –C.

3         Calcium binding to Troponin C exposes the Mysoin- Binding site in the actin.

4         The binding of actin and Mysoin occurs and  Myosin pulls the actin towards itself producing              active tension. ATP is not needed for Cross bridge linking.

5         The dissociation of actin and myosin is energy dependent. ATP is needed for this release of actin        myosin bond.

           Once the dissociation occurs, the ATP is hydrolysed to form ADP and Inorganic phosphate and the      myosin is put back to the high energy state with high affinity for actin being ready for next cycle       of cross bridging.

Steps of Skeletal Muscle contraction
Source:http://studylib.net/doc/9410005/steps-of-a-muscle-contraction

Know how  cadaveric spasm and Rigor mortis are different. 

Lets us take a special Consideration on the point no 5 (not from diagram). The release of actin from myosin needs ATP is the most important thing to describe physiology of post mortem rigidity.

Immediately after the death, the inherent tone of the muscle is lost and the initial state of flaccidity is seen known as the stage of Primary Flaccidity. In this stage, the somatic death has occurred but not the cellular death. So, the cell responds to electrochemical stimuli.

Once death occurs at the cellular level, the membrane permeability to all ions are disrupted and large amount of calcium is released from the sarcoplasmic reticulum causing the binding of actin and myosin which brings about the contraction. This is the stage of Rigor Mortis and the cells no longer respond to electro-chemical stimuli.

The separation of actin from myosin need ATP which is depleted once the cell dies. So they cannot separate and hence the muscle remains contracted.

After several hours of death, the autolytic enzyme released from the lysosomes gradually degrade all the proteins including actin and myosin causing the loss of stiifness after 15-20 hours. And hence the stage of Secondary Flacidity develops.

Know how  cadaveric spasm and Rigor mortis are different. 

Pupillary Reaction to Various Drugs and Substances

PUPIL REACTION TO SUBSTANCE/DRUGS

Pupil of human eye constrict and dilate depending upon the need of the eye to focus on near object/far object, dim light/bright light and whether it is under stress/not. This response is solely dependent upon the muscles inside the eyes in the iris. The pupillae constrictor muscle respond to cholinergic agents and cause pupillary constriction while the dilator pupillae muscle is acted upon by sympathetic system and causes pupillary dilation.

Beside these natural response, the substances we come in contact with can also alter the pupillary size. Drugs such as Adrenaline, antidepresssants, antihistaminics, can cause pupillary dilatation. Pethidine being an exception is the only opoid to cause pupillary dilation. Herbal products such as belladona, strychinine, calotropis and Chemicals such as alcohol, formic acid, cyanide Carbon monoxide also have dilatatory effect based upon the dosing.

Phenols, Organophosphate, carbamates, Carbolic acid, cause pupillary cosntriction. Drugs such as Opoids, barbiturates, Benzodiaepines, methyl dopa and plant product such as Nicotine, caffiene and opium causes the dilatation of pupil. 

Know how to assess the pupillary reaction or light reflex.

DILATORS		CONSTRICTORS
A6 C5 (Big1 Co Ca Cola Can)		O2 B2 C5 ( Car Car Caf )
Formic Acid			Phenol (Carbolic Acid)
Pethidine2 (only exception in Opoid)		O	All Opoids2  (Except severe Acidosis/hypoxia/ respiratory depression)
Adrenaline*/ Ephidrine/Sympathetomimetics	A		Parasympathetomimetics*
Atropine*/ Belladona/ Dhatura	A	O	Organophosphate*
Amphetamine	A	B	Barbiturates
Alcohol3	A	B	Benzodiazepines
Antidepressants	A
Antihistaminics	A
Cocaine Crack	Co	Car	Carbamate
Carbon Monoxide/ CO	Ca/CO	Car	Carbolic Acid
Calotropis	Cola	Caf	Caffeine
Cannabis	Can		Coma of Alcohol3
Cyanide			Clonidine
Hypothermia*			Heat Stroke*
Strychnine			Nicotine4
			Methyl Dopa

HIPPUS: Alternating dilatation and constriction is done by ACONITE

Note: All A’s constrict the pupil. All B’s and O’s dilate the pupil.

¹ Big is not a part of drug rather means dilatation.

² Only opoid to cause pupillary dilatation is Pethidine.

³ Toxic Effect of alcohol causes pupillary constriction as patient develops coma.

⁴ Delayed effect of Nicotine is dilatation of pupil.

* The drugs/substances in row with different color across the table are physiological Counterparts

  

Types of Wound: Superificial Abrsaion and Lacerated Wound

Drugs/Poisons resisting Putrefaction

Drugs/Poisons resisting Putrefaction

Organophosphorus

Edrin

Strychnine

Antimony

Arsenic

Nicotine

Dhatura

Yellow Oleander

@ OE SANDY

Difference between True bruise and Artificial Bruise

The concept of malingering has made it important to identify whether any bluish discoloration in the body is true bruise or bruise induced with use of various plant products. It is useful in forensic science to identify whether any assault / physical violence is true or the victim is fortifying the evidence to setup any guiltless.

True bruises can be present anywhere in the body and is generally associated with blister and itching. It changes color following the blunt trauma unlike false bruise which are stained by plant products and hence don’t change their color.

Click to know how is a respired lungs different from the unrespired lungs of a newborn.

Character	Artificial Bruise	True Bruise
Cause	Chemical Agent like plumbago, semicarpus, madar juice	Blunt Trauma
Location	Accessible part of body mostly	Anywhere
Blister	Present around the bruise	Not present
Itching	Present	Not Present
Color Changes	Absent	Characteristic
Fingers	Marks of scratching	Not so
Content	Acrid Serum	Extravagated blood
Chemical Analysis	Chemical detected	Not so

Difference between Chili and Dhatura

Character	Chilli	Dhatura
Size	Small	Large
Color	Yellow	Brown to black
Smell	Pungent	Odorless
Taste	Pungent	Bitter
Appearance	Round & Smooth	Reniform with pitted surface
Border	Convex Single edge	Concave with double edge
Section	Embryo curved inward	Embryo curved outward

Difference between respired and unrespired lungs (Live birth vs Dead Birth)

The knowledge whether a dead fetus was a still birth or died after coming into the environment (Live Birth) is very important in Forensic Science. This is important specially in countries where killing of neonate in the name of black magic is prevalent. Similarly, killing of female fetus/ newborn is also common in some part of the world. Killing a newborn is Crime in most part of the world and differentiation between the two can be made based upon the study of the lungs in the postmortem. 

Postmortem finding of a respired and unrespired lungs have many differences. The unrespired lungs is parenchymatous like a liver occupying lesser volume. Being condensed and no air particle inside it tends to sink in the water with density higher than that of water. 

Respired lungs on the other hand have spongy elastic appearance with lesser density and hence floats in water. It is expanded covering the heart and with respiration the cardiac circulation changes and the patency of the vessels is maintained making it ooze with frothy blood when cut into pieces.

The following are the characters based upon which the differentiation can be made between the two.

Character	Unrespired Lungs	Respired Lungs
Weight in relation to body weight	1/70	1/35
Volume	Small	Large and covers the heart
Consistency	Liver Like: Dense firm non crepitant	Soft, spongy, elastic, Crepitant
Extension	Up to the level of 4th and 5th rib	Up to the level of 6th and 7th rib
Specific gravity	1.04	0.94
Margin	Sharp	Rounded
Color	Uniform reddish	Mottled/ marbled appearance
Air vesicle	Not inflated	Inflated
Section	Little froth less blood exudates on pressure	Abundant frothy blood exudates
Breslow life test	Whole or part sinks	Expanded
Microscopy	Cuboidal lining	Squamous Epithelium
Blood vessel	Less patent	More Patent