Nociception

The detection of tissue damage by specialized transducers connected to A-delta and C-fibers.

Pain

An unpleasant sensory and emotional experience which we primarily associated with tissue damage or desribe in the terms of such damage, or both.

Classification of Pain Nociception

Acute (3)

Chronic

Proportionate to the stiumlation of the nocicpetor

When acute:  physiologic pain, serves a protective function, and normal pain

Chronic:  Pathologic

Neuropathic Pain Classification

(4)

Sustained by aberrant processes in PNS or CNS

Disproportionate to the stimulation of nociceptor

Serves no protective function

Pathologic Pain

Mixed Pain Classification

(2)

Nociceptive and Neuropathic Component

Idiopathic Pain Classification

(2)

No underlying lesion found yet, despite investigation

Pain disproportionate to the degree of clinically discernible tissue injury

Mechanism of Pathologic Pain:  General Considerations

(2)

Pain-processing mechanisms of function abnormally

Nociception is sustained by chronic injury

Mechanisms of Pathophysiologic Pain:  Peripheral Processes

(3)

Injury or diseased nerve(s)

Growth of axonal sprouts

Formation of ectopic foci

Mechanisms of Pathophysiologic Pain:

Central Sensitization Processes

(3)

Repeated impulse activity in C nociceptive neurons produces sensitization of STT neurons over time

Sensitization of STT neurons leads to increased spontaneous impulse activity and enhanced response to impulses in nociceptive and non-nociceptive primary afferents

Cause hyperalgesia, allodynia, and spontaneous pain

Pain Modulation Mechanisms

(4)

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