SITES OF PAIN

PAIN

One of the most important sensory mechanism mediated through specialized neural structures

SENSATIONS

Epicritic (Fine sensations)

A group fibers (Light touch, tactile localisation temperature between 25⁰C-40⁰C)

Protopathic (Crude sensations)

C group fibers (Pain and Temp above 40⁰C and below 25⁰
Deep Sensibility (Produced by stimulation of structures in deeper layers of skin, muscles, bones etc.. )

Pain:

Is Produced when an injurious (nociceptive) stimulus is received
It can be:
1. Mechanical (Cuts, blows)
2. Chemicals (acids)
3. Thermal (burn)
4. Disease

Pain:

Must be analysed in relation to:
1. SITE
2. RADIATION
3. CHARACTER
4. DURATION
5. FREQUENCY
6. TIMES OF OCCURENCE
7. AGGRAVATING AND AMELIORATING FACTORS
8. AND ANY ASSOCIATED PHENOMENA

TELEOLOGY (Importance of Pain)

Is pain good or bad ?

Good-Makes us conscious of the presence of the injurious agent
Bad-If it is counter productive to the interest of the patient. eg: In Cancer it only adds to the misery

TENDERNESS

It is the pain elicited by pressing the part

Characteristics of Pain

1. Threshold & Intensity

If the intensity is below threshold pain is not felt
Distraction of mind can increase the threshold of pain
Pain is also less when EPIS(endogenous pain inhibiting system) is overactive
Less emotional accompaniment
If do not express them

2. Adaptation

Pain receptors show no adaptation so the pain continuous as long as receptors continues to be stimulated

3. Localisation of Pain

Poorly localized
Superficial pain is better localized
Visceral pain is usually referred

4. Rate of damage on the intensity of Pain

If the rate of tissue injury is high intensity of pain is also high

How the Pain is produced ?

Stimulation of bare nerve terminals cause pain (RECEPTORS)
As soon as an a/c injury (STIMULUS) is received Pain is produced

First Pain:

Follows immediately after the injury causing the production of ALGOGENIC (Pain producing substance (AS)

Second Pain:

Long after the stimulus is over
Here pain is produced due to the production of ALGOGENIC substance (AS)

AS (Algogenic Substance) >> contact with Bare Nerve endings (Receptors) >> PAIN

Algogenic Substance (AS)

Eg:- Bradykinin
Serotonin
Potassium Ions
Acetyl Choline

PROSTAGLANDINS

Not algogenic but potentiate algogenic power of Serotonin & Bradykinin

ACTION OF PAIN KILLERS

Non steroidal anti-inflammatory agents (NSAIDS) inhibit the synthesis of prostaglandins (PG)

SOMATIC

VISCERAL

From Viscera
Eg:- Angina Pectoris
Peptic ulcer
Intestinal colic
Renal colic

VISCERAL PAIN

Viscus is insensitive to most of the sensory stimuli. Pain can arise from

1. Ischemia

Coronary artery occlusion resulting in myocardial ischemia Cardiac pain

2. Obstruction of a hollow viscus

Here the part proximal to obstruction contract violently so intestinal colic results. Pain is due to the contraction of the smooth muscles causing traction of the mesentery leading to pain

3. Inflammation

Here pain is due to associated spasm of smooth muscles

4. Distension

Too much distension of a hollow viscus can produce pain

REFERRED PAIN

Pain is not felt over the area where the viscus is situated but felt some where else

Features

1. Usually referred pain is felt at an area where the viscus was situated in the embryonic life
2. This is felt at the dermatome which corresponds to the viscerotome of pain producing viscus

ORGANS

And their response to painful stimuli

1. Brain: Is insensitive to Physical stimuli but large vessels and sinuses are sensitive
2. Heart:Is sensitive to chemical stimuli
3. Coronary arteries:Is sensitive to stretching
4. Pericardium:Is insensitive
5. Lungs:Visceral pleura is insensitive but parietal pleura is sensitive to stretching
6. Oesophagus:Is not sensitive to pain but appreciates warmth and cold
7. Abdominal Organs:Insensitive to cutting burning or clamping but sensitive to distension  (due to traction of the mesentery)
8. Liver and Spleen:Insensitive but pain may be felt on venous engorgement due to pressure
9. Genitourinary Organs (Kidney):Is insensitive but renal pelvis, ureter, Urinary bladder and urethra are sensitive

Pains of Special Interest

Intermittent Claudicition

This is recurrent pain in the calf muscle of leg during exertion which stops on rest
Here the pain is due to ischemia of the muscles producing P-factor which causes pain
During rest pain stops, P-factor is washed away by blood
Ischemia is due to failure of the blood vessels to cope up with additional requirement Necessary for the exertion

Thromboangitis Obliterans

(Buerger's disease) in which there is narrowing of the blood vessels or congenital vascular defect may be the cause for such condition

Inflammatory Pain

This is due to increasing tension causing pressure on nerve terminals as well as due to release of a chemical pain-producing factor

Ischaemic Muscular Pain

This condition is also due to the release of P-factor during active work. Ischaemia leads to accumulation where as circulatory flow washes out the P-factor The nature of P-Factor is not conformed. It may be potassium or a kinin

Angina Pectoris

Coronary Occlusion

In this condition, in addition to P-factor there is release of 5-hydroxy tryptamine and plasma pain producing polypeptide. The referred pain to the arm is due to the segmental distribution of nerves (C.2-5) to the arm; those are distributed to the heart through sympathetics

Pain of peptic ulcer

HCL acting on the ulcer (chemical stimulus)

Headache

It is believed to be due to distension of intracranial arteries. Changes in intracranial pressure also cause headache by stretching the walls of intracranial arteries or the sinus of dura mater. Migraine is a type of spontaneous unilateral severe headache, caused probably by distension of intracranial blood vessels

Stiff neck pain

This is due to sustained contraction of neck muscle resulting from a irritative focus

Nerve pain

Partial compression of a nerve root leads to irritability of the nerve or nerves concerned and gives rise to the formation of areas of hyperalgesia and paraesthesia