Title: A1261047609ayKli
1Pathophysiology of Pain
2Nociception
- The detection of tissue damage by specialized
transducers connected to A-delta and C-fibers
3Pain
- An unpleasant sensory and emotional experience
which we primarily associate with tissue damage
or describe in terms of such damage, or both
4Classification of Pain Nociception
- Proportionate to the stimulation of the
nociceptor - When acute
- Physiologic pain
- Serves a protective function
- Normal pain
- Pathologic when chronic
5Classification of PainNeuropathic Pain
- Sustained by aberrant processes in PNS or CNS
- Disproportionate to the stimulation of nociceptor
- Serves no protective function
- Pathologic pain
6Classification of Pain Mixed Pain
- Nociceptive components
- Neuropathic components
- Examples
- Failed low-back-surgery syndrome
- Complex regional pain syndrome
7Classification of Pain Idiopathic Pain
- No underlying lesion found yet, despite
investigation - Pain disproportionate to the degree of clinically
discernible tissue injury
8Normal Central Pain Mechanisms
9Peripheral and Central Pathways for Pain
Ascending Tracts
Descending Tracts
Cortex
Thalamus
Midbrain
Pons
Medulla
Spinal Cord
10Pain-Inhibitory and Pain-Facilitatory Mechanisms
Within the Dorsal Horn
0
C
A-DELTA
A-BETA
_ _
Neuronal circuitry within the dorsal
horn. Primary afferent neuron axons synapse onto
spinothalamic neurons and onto inhibitory and
excitatory neurons.
STTNEURON
TO BRAIN
11Rating of First and Second Pain Intensity
Adapted with permission from Cooper BY, et al.
Pain. 198624103 and from Lee KH, et al. In
Fields HL, Dubner R, Cervero F, eds. Proceedings
of the Fourth World Congress on Pain. New York,
NY Raven Press 1985204.
12Mechanisms of Pathologic Pain
13Mechanisms of Pathologic Pain General
Considerations
- Pain-processing mechanisms function abnormally
- Examples neuropathic pain syndromes
- Nociception is sustained by chronic injury
- Example arthritis
14 Mechanisms of Pathophysiologic Pain Peripheral
Processes
- Injured or diseased nerve(s)
- Growth of axonal sprouts
- Formation of ectopic foci
15Mechanisms of Pathophysiologic 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 in nociceptive and
non-nociceptive primary afferents - Causes hyperalgesia, allodynia, and spontaneous
pain
16Temporal summation of second pain (second pain
summation 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 the Treatment of
Chronic Pain New Concepts and Critical Issues.
Seattle, Wash IASP Press 199466.
17Mechanism of Central Sensitization Associated
With Tonic C Nociceptor Input
0
A-DELTA
A-BETA
C
Tonic activity in C nociceptors
_ _
STTNEURON
Enhanced postsynaptic effects by NMDA-receptor
sensitization
TO BRAIN
18Intracellular Mechanisms of Sensitization
Reproduced with permission from Mao J, et al.
Pain. 199561361.
19Loss of Inhibitory Interneuron Function
0
C
A-DELTA
A-BETA
Tonic activity in C nociceptors
_ _
STTNEURON
Enhanced postsynaptic effects by NMDA-receptor
sensitization
TO BRAIN
20Brain-to-Spinal-Cord Modulation of Pain
21Pain Modulation Mechanisms
- Brain centers/pathways that descend to the spinal
cord and modulate 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
22Pathophysiology of Pain Conclusion
- Neuronal plasticity
- Nociceptor, spinal cord, brain
- Pain-facilitatory and pathophysiologic mechanisms
- Wind-up phenomenon
- Central sensitization
- Modulating mechanisms
- Ascending
- Descending
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