PAin Pathway by Munir

8/7/2019 PAin Pathway by Munir

1/27

Physiolohy Of Pain

Presented by :

Dr. Monir O. Mhemed

Abusharib

1st year A@E master

student


2/27

Definition

Pain is an unpleasant sensory andemotional experience associated withactual or potential tissue damage

Although acute pain and associatedresponses can be unpleasant and oftendebilitating, they serve important adaptive

purposes. They identify and localize

noxious stimuli, initiate withdrawalresponses that limit tissue injury,

inhibit mobility thereby enhancing woundhealing.


3/27

Classifications

Pain has been classified into two major types

fast pain and slow pain.

Fast pain is felt within about 0.1 second after

a pain is applied, whereas slow pain stimulus

begins only after 1 second or more and thenincreases slowly over many seconds andsometimes even minutes.

the conduction pathways for these two types ofpain are different .

Fast pain is also called sharp pain,acute pain.Slow pain also goes by many names, such asslow burning pain, aching pain, and chronic pain.This type of pain is usually associated with tissuedestruction.


4/27

Pain receptors

Pain Receptors Are Free Nerve Endingswhich are also called nociceptors, theircell body lies in dorsal root ganglion and

the proximal end terminate at posteriorhorn of spinal cord. They are widespreadin the superficial layers of the skin as wellas in certain internal tissues, such as:

theperiosteum, the arterialwalls, thejointsurfaces, and the falxand tentorium in the

cranial vault.


5/27

Most other deep tissues are only

sparsely supplied with pain endings;

nevertheless, any widespread tissuedamage can summate to cause

the slow-chronic-aching type of pain

in most of these areas


6/27

Three Types of Stimuli Excite PainReceptors:

Mechanical, Thermal, and Chemical.

In general, fast pain is elicited by themechanical and thermal types of Stimuli.

whereas slow pain can be elicited by allthree types


7/27

Noxious stimuli are converted into a calcium ion(Ca2+) mediated electrical depolarization withinthe nociceptor

Some of the chemicals that excite the chemical

type of pain are bradykinin, serotonin, histamine,potassium ions, H, acetylcholine, and proteolytic

enzymes.

In addition, prostaglandins and substance Penhance the sensitivity of pain endings but do not

directly excite them.The chemical substances are especially importantin stimulating the slow, suffering type of pain thatoccurs after tissue injury


8/27


9/27

In contrast to most other sensory receptors of the body,

pain receptors adapt very little and sometimes not at all.

In fact, under some conditions, excitation of pain fibers

becomes progressively greater, especially so for

slow-aching-nauseous pain, as the pain stimulus

continues.This increase in sensitivity of the pain receptors

is called hyperalgesia. One can readily understand

the importance of this failure of pain receptors to

adapt, because it allows the pain to keep the person

apprised of a tissue-damaging stimulus as long as itpersists.


10/27


11/27

second-order neurons cross immediately to theopposite side of the cord through the anteriorcommissure and then turn upward, passing to

the brain in the anterolateralcolumns.

Termination of the Neospinothalamic Tract inthe Brain Stem and Thalamus.A few fibers

of the neospinothalamic tract terminate in thereticular areas of the brain stem, but most pass

all the way to the thalamus without interruption,

terminating in the ventrobasalcomplexalong withthe dorsal column tract for tactile sensations.


12/27


13/27

Localization offast pain

Fast pain is well localized ,however

when only pain receptor is stimulatedwithout simultaneous simulation of

tactile receptor even fast pain will be

poorly localized


14/27


15/27

continue

Only 1/10- 1/4 of the fiber terminate

in the thalamus,most of the fibers

terminate at:

Reticular nuclei in the medulla,pons,

periaqueductal grey region

surrounding the aqueduct


16/27

3rd order neuron project to the

somatosensory area in the cortex

where it relay on 4th order neurons

Cerebral cortex plays an essential

role in interpreting the quality of pain,

even though pain perception is the

function of the lower centres


17/27

Poor localization of pain is due tomultisynaptic,diffuse connectivity of

this pathway


18/27

Reffered pain

Often a person feels pain in a part of

the body that is fairly remote from the

tissue causing the pain. This is calledreferred pain.

Pain referto astructure that originate

from the same embryonicsegment ofthe structure at which pain originate


19/27


20/27


21/27

Because both neurons relay on thesame 2nd order neuron


22/27

Descending inhibitory pathway

Pain is modulated at spinal level by

inhibitory tracts originate from:

cerebral cortex, hypothalamus,

thalamus,PAG region, these neurons

stimulates inhibitory intrneurons.

These inhibitory pathway are

influenced by pts psychological andemotional status


23/27

anxiety, psychological stress and

depression reduce the activity of theinhibitory pathway, thereby lowering

the threshold for pain and increasing

pain sensetivity score


24/27

Hyperalgesia

Defined as state of increased pain

sensitivity and enhanced perception

following acute injury that may persist

chronically.

The hyperalgesic region may extend to

dermatomes above and below the area

of injury and is associated with ipsilateral(and occasionally contralateral)

muscular spasm/immobility.


25/27

continue

Primaryhyperalgesia

Increased pain sensitivity at the injurysite Related to peripheral release of

intracellular or humoral noxious

mediators


26/27

Secondaryhyperalgesia

Increased pain sensitivity at adjacent,uninjured sites Related to changes in

excitability of spinal and supraspinal

neurons


27/27

The end

Thank you

PAin Pathway by Munir

Documents

Transcript of PAin Pathway by Munir