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7/21/2019 pain-100306152548-phpapp02


7/21/2019 pain-100306152548-phpapp02


PAIN SENSATIONPAIN SENSATION

According to The International Association for the Study of Pain (IASP):

Definition: Pain is an unpleasant sensory and emotional experience

associated ith actual or potential tissue damage!

Significance

") arning signal against tissue damage! Pain is one of the most

prominent symptoms of tissue damage.

#) Initiate protecti$e reflexes which causes the subject to get rid of the

painful stimulus, or at least, to minimize tissue injury or damage

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If persistent, physiological pain may progress to aIf persistent, physiological pain may progress to a pathological conditionpathological condition

itself, often referred to asitself, often referred to as maladaptivemaladaptive pain, in which case pain ispain, in which case pain is

dissociated from the original noxious stimulation or the healing processdissociated from the original noxious stimulation or the healing process

and thus does not represent anymore a symptom of disease but ratherand thus does not represent anymore a symptom of disease but rather

abnormal sensory processing due toabnormal sensory processing due to damage to tissuesdama

ge to tissues (inflammatory(inflammatory

pain) orpain) or the nervous systemthe nervous s

ystem (neuropathic pain), or to(neuropathic pain), or to abnormal functionabnormal function

of the nervous system itself (functional pain)of the nervous s

ystem itself (functional pain)..

pain resulting from activation of pain receptors may be referred to aspain resulting from activation of pain receptors may be referred to as

adaptiveadaptive oror physiologicalphysiological pain, because it minimizes tissue damage andpain, because it minimizes tissue damage and

promotes healing.promotes healing.

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%lassification:

Pain is classified into nocicepti$e, neuropathic and psychogenic all

can be either acute or chronic!

Pain is defined as chronic if persists more than ! wee"s.

"! Nocicepti$e is pain caused &y tissue damage (inflammation) which stimulate

pain receptors (nociceptors).

#! Neuropathic: (pain due to in'ury of ner$e pathay)site of in'ury: #entral#entral #entral pain (thalamic infarct).

$ixed$ixed Plexus avulsion, Post herpetic neuralgia.

PeripheralPeripheral %euroma, nerve compression, phantom, neuralgias.

character: burning, tingling, numbness, pressing, s&ueezing, itching, constant '

intermittent shooting, lancinating, electric.

! Psychogenic: (difficult to differentiate hether secondary to or actual cause

of pain) anxiety, depression (*+ of depressives complain of pain on initial

presentation).

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Pain *eceptors (Nociceptors)

Types of Pain Receptors

-ree nerve endings which are morphologically similar but functionally

specific . hey are classified according to their sensitivity into/

Polymodal Pain *eceptors (most pain receptors)

hese respond to a combination of mechanical, thermal, and chemical

noxious stimuli.

+echanical Pain *eceptors

respond to strong mechanical forces, such as cutting, crushing, pric"ing, or

even firm pressure on tissues.

Thermal Pain *eceptors respond to excessive changes in temperature (above 01o# and below 2+o#).

%hemical Pain *eceptors

respond to noxious chemical stimuli.

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Distribution of Pain Receptors

Pain receptors are found in most tissues of the body but varies in their density.

hey are abundant and widely spread in the skin and some internal

tissues such as/ the periosteum of the bone,

arterial walls,

joint surfaces,

the dura of the falx and tentorium in the cranial cavity,

the s"eletal muscle,

the parietal layer of serous membranes.

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$any of the other deep tissues and viscera are poorly supplied with pain

receptors. 3o,

for pain to occur, painful stimulus must by intense and widespread.

he deep 4 visceral pain are poorly localized.

5n the other hand, the brain itself and also the parenchymal tissues of the

liver , kidneys, and lungs have no pain receptors. hey are called 6pain

insensitive structures7

N.B.: erious diseases in these structures don!t produce pain till they

e"tend to a pin sensitive structure like arterial wall or serous covering.

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Pain Threshold:

Pain threshold is the lowest intensity of stimulus that can cause pain when

the stimulus is applied for sufficient period of time.

Pain threshold can be measured in many ways.

5ne of the accurate methods to &uantify the threshold is heating the s"in with

measured amounts of radiant heat from a calibrated electric lamp.

It has been shown that the majority of subjects begin to perceive pain when the

s"in temperature reaches 01o#, and almost everyone perceives pain before the

temperature reaches 0!o#.

3o, it seems that the great majority of people do not show significant

differences in their sensitivity to painful stimuli. 8owever, they differ widely in their

reaction to pain.

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timulation of Pain Receptors:

noxious stimuli are strong enough

9 tissue damage 9 release of

chemical agents from destructed cells

into the surrounding interstitial spaces

which are called #pain producing

compounds$ %PP&s' 9 stimulate

pain receptors in the affected tissues.

PGE2

IL-1

Both threshold of painreceptors facilitating their

stimulation

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he PP#s may be classified into/

", -irect stimulators", -irect stimulators

3ubstances which when reach

specific threshold directly stimulate

pain receptors 9 pain, as/

, ./ ions! , 0/ ions

, Serotonin! , 0istamine

, 1rady2inin

#, Sensiti3ers#, Sensiti3ers

3ubstances which lower the threshold for

stimulation of pain receptors by direct

stimulators 9 facilitate pain

production. hey include/

a' ubstances released by the in(ured

tissues as/ P:;< 4 I=2

b' ubstances released by pain

receptors through antidromic impulses

as/ substance P

%.>./ 3ubstance P also stimulate mast

cells to release histamine which is a

direct stimulator.

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he surface membrane of pain receptors contain several molecular receptors

which can be activated by various PP#s.

$olecular receptor -unction

?cid sensing receptor (8') 3timulationPurinergic receptor (?P) 3timulation

ransient receptor potential rec.(thermal)

3timulation

>rady"inin receptor 3timulation

4 sensitization

8istamine recptor 3timulation

4 sensitization

3erotonin receptor 3timulation

4 sensitization

Prostaglandin receptor sensitization

Interleu"in2 receptor sensitization

3ubstance P receptor sensitization

#annabinoid receptor Inhibition

5pioid receptor Inhibition

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Pain Tolerance:

It is the maximum intensity of pain can be tolerated by the subject without obvious

complaint.

Pain tolerance is affected by a number of factors/

?nxiety, depression 4 fatigue 9 pain tolerance.

rest, sever exercise 4 strong emotional excitement 9 pain tolerance.

Non Adaptation of Pain *eceptors

Pain receptors do not adapt to continuing noxious stimuli.

%on adaptation to pain serves a protective function to "eep the individual

trying to remove the damaging stimulus or to get away from it.

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T0E %0A*A%TE* (45A6IT7) of pain

") Pric2ing or %utting Pain

#) 1urning Pain

) Aching Pain

8) Thro&&ing Pain

9) %olic2y Pain

? sharp and localized pain. It is of cutaneous origin and is caused by pric"ing or

cutting the s"in by a sharp object.

? less well localized pain. It is usually of cutaneous origin and is caused by burns

or inflammations of the s"in .

? dullaching nature. It is more diffuse and felt coming from deeper tissues, e.g.

rheumatic pains.

is characterized by fluctuation of its intensity with arterial pulsations. It results

from localized inflammation in deep tissues, as in abscess formation.

Pain results from spasm of plain muscles in the walls of hollow viscera.

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Somatic isceral

sitesite cutaneous, deep tissues sympathetically innervatedorgans can be transferredto body surface

character character constant, localisedaching, throbbing, gnawing

vague distribution and@uality deep, ache, dragging,s&ueezingacute/ colic, paroxysmal, '%A, sweating, >P and heartrate changes

Acute nocicepti$e pain:Acute nocicepti$e pain:

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-ast (Immediate) physiologicalpain

3low (delayed)pathophysiological pain

onset: during application of the stimulus

Duration: short duration.

Nature: pric"ing

)ocali*ation: welllocalized

+fferent: ?delta fibers

,igher center: ##

Neurotransmitter: glutamate

ignificance: B determine site 4 severity.B Initiate withdrawal reflexes.

+bolished by deep pressure and not

abolished by morphine.

3hortly after application if tissue

damage occurs

=onger duration

>urning

Poorlylocalized

#fibers

halamus

3ubstanceP

B ?ssociated with arousal, autonomic 4

emotional reactions

?bolished by local anaethesia 4

morphine

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*eactions to Pain:

-' omatic otor Reactions

/' +utonomic Reactions

0' 1motional and Psychogenic Reactions

2' ,yperalgesia.

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-' omatic otor Reactions

a) Excess neuromuscular excita&ility throughout the body.

&) ;ithdraal *eflexes!

initiated by cutaneous pain.

?im to withdraw the whole body or a part of it away from a painful

stimulus mainly by contraction of flexor muscles.

It is a prepotent reflex inhibit all other reflexes during its occurrence.

Ceflex spasm of the nearby s"eletal muscles in case of deep pain 9

minimize mobilization of the pained part 9 stimulation of pain

receptors.

c) Immo&ili3ation *eaction!

d) <uarding *eaction!

Ceflex spasm of the overlying s"eletal muscles in case of visceral pain

9 stimulation of pain receptors in the diseased viscus.

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/' +utonomic Reactions

ild &utaneous pain 9 a pressor reaction D rise of blood pressure

and heart rate, mediated by sympathetic stimulation.

ever cutaneous3 deep and visceral pain 9 a depressor reaction

associated with hypotension, bradycardia, and nausea, due to parasympathetic

stimulation.

uch pain is often described as sickening pain and may be accompanied

by vomiting.

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0' 1motional and Psychogenic Reactions

+n"iety , fear , crying , depression, as well as the feeling of being hurt may

be felt by the pained person.

these reactions vary/

-rom person to person on exposure to similar pain stimuli.

in the same person according to his emotional state/

4orry about the cause of pain augment the feeling of pain. hus, Patients

suffer than healthy subject to the same degree of pain.

trong emotional e"citement 5 sever physical e"ertion may bloc" the feeling

of pain. hus, seriously wounded soldiers in a battlefield suffer little or no pain till the

battle is over.

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NE5*A6 PAT0;A7S =O* PAINPain impulses are transmitted to #%3 by two separate pathways, which

correspond to the two different types of pain a fast6acute %pricking' pain, and a

slow6chronic %burning or aching' pain.

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%utaneous 0yperalgesia

Definition: Increased s"in sensitivity to pain.

Types: 2 Primary hyperalgesia. < 3econdary hyperalgesia.

2 Primary hyperalgesia < 3econdary hyperalgesia

Eevelop *+F+ min. after injury.

=asts for several hours or days.

In the area of redness.

%onpainful stimuli (as touch)

becomes painful.

echanism:

Eecreased pain threshold due to

local axon reflex releasing

substance P

Eevelops later.

3horter duration than 2ry.

In healthy s"in surrounding red area.

Pain is felt more sever than normal.

#entral sensitization explained by

convergence6facilitation theory.

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*eferred PainDefinition: Pain felt away from the original site of the painful stimulus.

Radiating pain: Pain which appear to migrate away from its original site.

Ceferred pain is a part of radiating pain.

7isceral pain is usually referred.

Deep pain may be referred.

&utaneous pain is never referred.

ite of referral is determined by dermatomal rule/

he pain from a viscera is referred to a somatic structure (s"in or deep structure)

which were developed in the same embryonic segment and supplied by the same

dorsal root ganglia.

+bnormal sites are due to migration of viscera.

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echanism of referred pain %&onvergence6pro(ection theory':

%erves from viscera and from a somatic structure developed in the same

embryonic segment develops from the same EC: and converge to a great extent

on the same 3:C.

hus, visceral pain afferents usually excite the same spinothalamic tract neurons

and the same neurons in the higher centers that are activated by the pain afferents

from somatic structures to which the visceral pain is referred.

>rain is accustomed to receive pain impulses from somatic structures as the

fre&uency of somatic pain is much more fre&uent than the visceral pain.

hus, the brain would misinterpret the origin of the visceral pain impulses, and the

pain is perceived as if arising from the s"in area or deep somatic structures which

are innervated by the same spinal segments that innervate the diseased viscera.

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1 l f R f d P i f 7i l 8

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1"amples of Referred Pain from 7isceral 8rgans

"!%ardiac Pain

is referred mainly to the base of the neck , over the left shoulder , inner side

of the left arm, and under the sternum %retrosternal'.

?ll these structure developed from embryonic segments which enter the spinal

coed along <,*,0,1 thorathic nerves.

#! <all 1ladder Painis referred to epigastric region, slightly to the right, and if an inflammed gall

bladder irritates the diaphragm, the pain may also be referred to the tip of the right

shoulder 4 small area at the tip of the right scapula.

! *enal and 5reteric Pain

is usually felt directly behind the diseased viscera in the bac". 8owever, the pain

is occasionally referred to the anterior abdominal wall near the inguinal region3

scrotum 5 testis (=2).

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8! Appendicitis Pain

is initially referred to a remote area around the umbilicus (h2+), but when the

inflammatory process spreads to the overlying parietal peritoneum the pain is also

localized in the right iliac fossa just over the site of irritation.

9! <astric Pain

is usually referred to the s"in of epigastric region in the anterior abdominal

wall between the "yphoid process and the umbilicus.

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*elief of pain (analgesia)

This may be done by:

-6 Physiological method %edogenous analgesic system'.

/6 Pharmacological.

06 urgical by many methods as cutting of the peripheral nerves. Prefrontal

lobectomy may be used in sever cases. 9t abolishes only the emotional and

psychogenic effect of pain but associated with sever personality changes.

o3 this method is used in terminal stages of severly painful conditions as

tumour.

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T0E PAIN %ONT*O6

S7STE+

also called the endogenous

analgesic system.

consists of special areas in the

brain and spinal cord, which when

activated can greatly reduce or

even completely abolish pain

sensation.

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)ocation

2he periaueductal gray area %P+; area' around the a&ueduct of sylvius in

the midbrain and pons.

<he raphe magnus %NR' nucleus located in the lower region of the pons and

upper region of the medulla.

*he nucleus reticularis paragiganto 6cellularis in the medulla.

0 )ocus ceruleus %N&' in pons

1 ? pain inhibitory comple" located in the dorsal horn of the spinal cord

(probably in laminae II and III / the substantia gelatinosa of Colandi).

8pioid Peptides

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8pioid Peptides

;ndogenous naturallyoccurring physiologic peptides which are similar in

structure and function to opium (Dmorphine).

hey can bind to the morphine receptors 9 produce longlasting analgesiceffect.

he opioid peptides consist of three major groups / he enkephalins, the

endorphins, and the dynorphins.

8piate Receptors

hree different types of opiate receptors have been characterized / delta (G),

"appa ("), and muta (H)

>inding of opioid peptides with opiate receptors at specific sites in the nervous

system functions to stop synaptic transmission of pain impulses through

the central pathways of pain.

#an be bloc"ed by nalo"one, which is a morphine antagonist

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+ctivation of the Pain &ontrol ystem

%linical (Experimental)%linical (Experimental) Natural (physiological)Natural (physiological)

2 ;lectrical stimulation of certain

regions of pain control system

< =ocal application of opiates (such

as morphine) at particular regions in

the nervous system.

%pharmacological anesthesia'

;xposure to severe stress,

particularly when associated with

strong emotional e"citement .

%!%!6im&ic system

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PA< +id&rain

Peri$entricular area of the hypothalamus

y

*eticular formation

A s c e n d i n g

p a i n p a t h a y

//

// /

:?>?

,,, //6%6% N*+N*+:?>?

,,, //

3erotonin ///

;pinephrine ///

Pons

Spinal %ord

"st order neur on in the pain pathay#nd order neuron in the pain pathay

8 o w s t r e s s a c t i v a t e s t h e p a i n c o n t r o l s

y s t e m I

8 o w s

t r e s s a c t i v a t e s t h e p a i n c o n t r o l s

y s t e m I

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;n"ephalin binds to opiate receptors in/

2 #entral terminal of 2st order neuron

9 opening of #l channel 9 #l

influx 9 hyperpolarization 9

bloc" of #a influx 9 inhibit release

of chemical transmitter from 2st order

neuron

< postsynaptic <nd order neuron in

pain pathway 9 opening of J

channels 9 hyperpolarization 9

inhibit their response to the pain

chemical transmitter.

PAIN <ATE %ONT*O6

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PAIN <ATE %ONT*O6 he sites of synapses along the pain

pathway are considered as gates through

which pain transmission can be facilitated (if

the gate is open) or blocked (if the gate is

closed).

he main pain gates are/

-6 pinal gate: at the 3:C.

/6 Brain stem gate/ at the nuclei of reticular

formation.

06 Thalamic gate: ?t neurons of PA=% 4

intalaminar thalamic nuclei.

"

#

? h i l

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?t the spinal gate/

Pain transmission is &loc2ed &y:

2 Eescending inhibitory impulses through the pain control system activating

en"ephalinsecreting interneuron (see before)

< 3timulation of the =arge Eiameter terminating peripherally in

mechanoreceptors, such as tactile receptors or proprioceptors. his may explain

why simple maneuvers such as rubbing the s"in (thus exciting tactile and pressure

receptors), near a painful area is often effective in relieving certain types of pain.

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Impulses from

tactile receptors

/

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, Acupuncture

?cupuncture has been practiced in #hina for more than 0+++ years as a method

for pain relief.

echanism:echanism:

2 needles in appropriate body regions are thought to excite certain sensory neural

pathways which feed into the brain stem centers (such as the P?:) involved

in the pain control system, with release of endogenous opioid peptides.

< simultaneous suppression of pain transmission at the spinal paingate by

acupuncture

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