2 Main reasons:

1. tissues coverings injury;

2. oxygen respiration level changing:

1. any substances disturbing oxidative processes in tissues plus

2. blood supply stoppage

↓

pain

↓

sympathetic nervous system activation

↓

Injured organ oxygen consumption inhibiting

↓ ↓

compensation of oxidative processes trophycs improvement

Insufficiency in it

↓

tissular respiration coming to norm

Pain sensation has two components:

1) Fast pain

2) Slow pain.

According to another classification, there are several pain components:

1) sensory – it is expressed in sensation;

2) affective – unpleasant emotions;

3) vegetative:

• skin vessels dilation;

• blood supply improvement leads to skin reddish;

• skin vessels vasoconstriction;

• circulation decreasing leads to skin palor;

• hypotension;

• tahysphygmy (frequent pulse);

• midriasis (pupils dilation);

• respiration rhythm changing;

• at biliary colics – nausea, vomiting, hypotension, excessive sweat releasing;

4) motor:

• reflex of avoiding or protection (for instance, at external injury);

• muscular tension – at deep or visceral pain;

5) behavioral reactions;

6) consciousness;

6) memory;

8) motivations.

Pain classification:

a) acute or epicritic:

• it is recognized rapidly;

• it is determined easily;

• adaptation is developed quickly to it;

• it lasts not longer than stimulus action;

• it is delt with nervous fibers of A_δ type (fast, conductance velocity is equal to 4-30 m/sec);

b) chronic or protopathic:

• it is recognized slowly;

• it is localized badly;

• it lasts for long time;

• it is not accompanied by adaptation development;

• it is more ancient than epicritic pain;

• it is less perfect as a signal of danger;

• it is linked with fibers of C type (speed is up to 3 m/sec).

By occurrence place:

1) somatic:

а) superficial (from skin): pinching, puncture; it is differentiated by appearance time:

*early;

*late;

b) deep (from muscles, bones, joints, connective tissue): acute, subacute and chronic pain in joints; fits; headache;

2) visceral – from inner ogans: biliary colics, ulcer, appendicitis, spasms and others.

Special forms:

a) projected – state, at which the locus to which injuring stimulus acts to does not coincide to the place where one can feel the pain;

b) neuralgia – subtype of projected pain when pain in the innervation region are observed at continuous irritations of nerve or posterior spine root;

c) reflected – painful sensations caused by injuring irritations of inner organs are located not in a given organ but in separate surface locuses:

• itch;

• causalgias – burning stable continuous pain without definite reasons;

d) central pain:

• “painful anaesthesia” after posterior roots removal;

• phanthomic pain – after amputations;

• thalamic pain – at sensory ventral thalamic nuscle diseases; it is characterized by very big power.

Whenever a pain stimulus is applied, first a bright, sharp and localized pain sensation is produced. This is called fast pain. It is followed by a dull, diffused and unpleasant pain. This is known as slow pain.

The receptors for both components of pain are the same, i.e. free nerve endings. But afferent nerve fibers are different. The fast pain sensation is carried by A5 (g) fibers and the slow pain sensation is carried by С type of nerve fibers.

Receptors of both components of pain are free nerve endings. Free nerve endings are distributed throughout the body.

Scientists tell about 2 nociceptors types:

mechanoreceptors - mechanic action leads to receptor membrane depolarization, permeability increasing for sodium ions in nervous fiber; then receptory potential and action potential (in nervous fiber) appear;

chemonociceptors – react to the substances changing oxidative processes in tissues:

– hydrochloric acid;

– sulphuric acid;

– acetic acid;

– histamine;

– acetylcholine;

– hydrogen ions excess;

– potassium ions excess;

– somatostatin;

– sunstance P;

– prostaglandines E₁, E₂, F_2α (aspirine, amidopyrine, analgine inhibit their formation).

Nociceptors location:

• skin;

• muscles;

• joints;

• epiosteum;

• subcutaneous cellulose;

• inner organs;

• vascular walls (big amount!).