IPHREHAB : PAIN cause and why?

IPHREHAB
PAIN

• Unpleasant sensation.
• Localised or not localised.
• Described differently.
• Associated anxiety and urge to escape or terminate the feeling.
• Dualality.

• Acute pain associated with behavioural arousal and stress response
• Increased BP, pupil size, plasma cotisol
• Local muscle contraction (limb flexion, abdominal wall rigidity)

PERIPHERAL MECHANISMS

1. Primary Afferent Nociceptors
2. Peripheral nerve containing three different types of axons-motor, sensory, sympathetic post ganglionic.
3. Cell bodies in dorsal root ganglion.
4. Two processes, peripheral and central.
5. Primary afferent are Aδ & C (unmelinated) axons.
6. Fibers present in skin and deep somatic and visceral structures.
7. Most of these fibers respond maximally only to intense painful stimulus and produce subjective experience of pain when electrically stimulated
8. This defines them as primary afferent nociceptors.
9. Nociceptors respond to many different stimuli- heating, intense mechanical stimuli (pinch), irritating chemicals.

Sensitisation

• Intense, repeated and prolonged stimuli to an inflamed tissue lowers the threshold for activating primary afferent nociceptors.
• Frequency of firing is higher.
• Mediators like bradykinin, PG’s, LT contribute. 
• Even innocuous stimulus can produce pain

• Clinically important as it contributes to tenderness, soreness, and hyperalgesia.
• Sensitisation has importance in visceral tissue.
• Normally viscera is insensitive but in presence of inflammatory mediators, the sensitivity increases especially to mechanical stimulus.
• Such afferents are termed as silent nociceptors

Nociceptor induced inflammation

• Neuroeffector function
• Contan polypeptides in peripheral terminals - substance P.
• Released from primary afferent nociceptors causing v/d, degranulation of mast cells, chemoattractant and increases production and release of inflammatory mediators.
• Tissue protectors due to these mechanisms.

CENTRAL MECHANISMS

• Spinal Cord and Referred Pain
• Afferent Axons enter dorsal root→ dorsal horn → spinal neurons.
• Each afferent neuron contacts many spinal neurons and each spinal neuron receives convergent input from many primary afferents.
• Convergence takes place and this underlies the phenomenon of referred pain.

Ascending Pathways

Afferent neuron → Spinal neurons → contra lateral side → spinothalamic tract → thalamus (several regions) → cerebral cortex (several regions).

Spinothalamic tract is crucial as damage causes impairment in transmission of these sensations.