Pa Tho Physiology of Pain

8/6/2019 Pa Tho Physiology of Pain

1/22

Pathophysiology of PainPathophysiology of Pain


2/22

Nociception

The detection of tissue damage by

specialized transducers connected to

A-delta and C-fibers


3/22

Pain

An unpleasant sensory and

emotional experience which we

primarily associate with tissue

damage or describe in terms of such

damage, or both


4/22

Classification of Pain

Nociception

Proportionate to the stimulation of

the nociceptor

When acute

Physiologic pain

Serves a protective function

Normal pain Pathologic when chronic


5/22

Classification of Pain:

Neuropathic Pain

Sustained by aberrant processes in

PNS or CNS

Disproportionate to the stimulation

of nociceptor

Serves no protective function

Pathologic pain


6/22


7/22


8/22

Normal Central Pain

Mechanisms


9/22

Peripheral and Central Pathways for

Pain Ascending TractsAscending Tracts Descending TractsDescending Tracts

Cortex

Midbrain

Medulla

Spinal Cord

Thalamus

Pons


10/22

Pain-Inhibitory and Pain-Facilitatory

Mechanisms Within the Dorsal Horn

A-DELTAA-BETA C

Neuronal circuitryNeuronal circuitry

within the dorsal horn.within the dorsal horn.

Primary afferent neuronPrimary afferent neuron

axons synapse ontoaxons synapse onto

spinothalamic neuronsspinothalamic neurons

and onto inhibitory andand onto inhibitory and

excitatory neurons.excitatory neurons.TO BRAIN

+ +

+_ _

+

0

STTSTTNEURONNEURON

STTSTTNEURONNEURON


11/22

Rating of First and Second

Pain Intensity

Adapted with permission from Cooper BY, et al.Adapted with permission from Cooper BY, et al. Pain.Pain. 1986;24:1031986;24:103andandfrom Lee KH, et al. In: Fields HL, Dubnerfrom Lee KH, et al. In: Fields HL, Dubner

R, Cervero F, eds.R, Cervero F, eds. Proceedings of the Fourth World Congress on Pain.Proceedings of the Fourth World Congress on Pain. New York, NY: Raven Press;1985:204.New York, NY: Raven Press;1985:204.


12/22

Mechanisms of Pathologic

Pain


13/22

Mechanisms of Pathologic Pain:

General Considerations

Pain-processing mechanisms

function abnormally

Examples: neuropathic pain syndromes

Nociception is sustained by chronic

injury

Example: arthritis


14/22

Mechanisms of Pathophysiologic

Pain: Peripheral Processes

Injured or diseased nerve(s)

Growth of axonal sprouts Formation of ectopic foci


15/22

ec an sms o a op ys o og c

Pain:

Central Sensitization Processes

Repeated impulse activity in C

nociceptive neurons produces

sensitization of STT neurons over time Sensitization of STT neurons leads to

Increased spontaneous impulse activity

Enhanced responses to impulses innociceptive and non-nociceptive primaryafferents

Causes hyperalgesia, allodynia, and

spontaneous pain


16/22

Temporal summation

of second pain

(second painsummation is a result

of repeated input from

C-fiber).

Temporal summation of

responses of a dorsal

horn (STT) neuron to

repeated C-fiber

stimulation and the

effects of the NMDA-receptor antagonist

ketamine.

Reproduced with permission from Price DD, et al. In: Fields HL, Liebeskind JC, eds. Pharmacological Approaches to theTreatment of Chronic Pain: New Concepts and Critical Issues. Seattle, Wash: IASP Press; 1994:66.


17/22

Mechanism of Central Sensitization Associated

With Tonic C Nociceptor Input

Enhanced postsynaptic

effects by NMDA-

receptor sensitization

Tonic activity in

C nociceptors

A-DELTAA-BETA

TO BRAIN

+ +

+_ _

+

0

STTSTTNEURONNEURON

STTSTTNEURONNEURON

+

+++ +

C


18/22

Intracellula

r

Mechanism

s of

Sensitizati

on

Reproduced with permission from Mao J, et

al. Pain. 1995;61:361.


19/22

Enhanced postsynaptic

effects by NMDA-

receptor sensitization

Tonic activity in

C nociceptors

A-DELTAA-BETA

TO BRAIN

+ +

+_ _

+

0

STTSTTNEURONNEURON

STTSTTNEURONNEURON

+++ +

Loss of Inhibitory Interneuron

FunctionC


20/22

Brain-to-Spinal-Cord

Modulation of Pain


21/22

Pain Modulation

Mechanisms

Brain centers/pathways that

descend to the spinal cord andmodulate pain

Tail-flick test

Off-cells inhibit transmission of

pain-related information to the brain

On-cells facilitate transmission of

pain-related signals to the brain


22/22

Pathophysiology of Pain:

Conclusion Neuronal plasticity

Nociceptor, spinal cord, brain

Pain-facilitatory and pathophysiologic

mechanisms

Wind-up phenomenon

Central sensitization

Modulating mechanisms

Ascending

Descending

Pa Tho Physiology of Pain

Documents

Transcript of Pa Tho Physiology of Pain