Neurophysiology of Pain
DR. KARISHMA R. PANDEYASSISTANT PROFESSOR
DEPARTMENT OF BASIC AND CLINICAL PHYSIOLOGY
Topics 1) What is pain?2) Types3) Receptors4) Stimulated by5) Pathways 6) Visceral pain7) Referred pain8) Projected pain/ phantom pain9) Modulation
What is pain?Pain is an unpleasant experience associated with acute tissue damage.
Experienced: 1) following injury,2) organic diseases such as advanced cancer, 3) its origin within the CNS itself (not associated with tissue damage)Accompanied by4) emotional reaction (fear or anxiety)5) autonomic responses such as sweating and an increase BP and HR.
Sherrington “Pain is the physical adjunct of an imperative protective reflex." Painful stimuli generally initiate potent withdrawal and avoidance responses.
Functions of Pain
Protects body against further injury Guides functional recovery May enhance disability
ClassificationFast Pain Slow Pain
2-5 micro met dia 0.4-1.2 miro met dia12-30 m/s 0.5-2 m/s
A fibre C fibreMonomodal Polymodal
Activated by either high intensity mechanical stimuli or thermal stimuli(<50C)
Activated by high intensity mechanical, chemical and thermal (both hot and cold) stimuli
Glutamate Substance P or CGRPFollow neospinothalamic tract Follow paleospinothalamic tract
Nociceptors
• Responsive to noxious/ painful stimuli
• Free nerve endings
• Non-adapting nature
• Stimuli1) Mechanical2) Thermal: <5 or >45
0C3) Chemical
Receptors
Vanilloid receptor-1 (VR1): Vanillins, capsaicin, protons and to potentially harmful temp >43 °
VRL-1: temp > 50 °
Organization of Spinal Cord
Anterolateral Pathway: Spinothalamic Pathway
Sensations of pain, thermal and crude touch
Neospinothalamic Pathway: Fast Pain (More Localized)
Paleospinothalamic Pathway: Slow Pain (Less Localized)Diffuse projection to cerebral cortex and limbic system
Visceral pain
Deep pain Pain in deeper region of the body especially due to injuries to bones, tendons, and
joints dull aching and poor localization (probably d/t relative deficiency of Aδ nerve
fibers) Usu accompanied by prolonged contraction of skeletal muscles--- induce
ischaemia and aggravate pain
Pain in visceral organs. chronic-aching-suffering type of pain, st burning and intense sharp pain
Diffuse and poor localization Causes of pain are distention of organ, chemical irritation or ischemia Muscle spasm and rigidity (guarding) Pain impulses are carried by C fibers. pain often radiates or is referred to other areas
Referred Pain Often a person feels pain
in a part of the body that is fairly remote from the tissue causing the pain is called referred pain
Mechanism of Referred Pain
Projected Pain
Phantom Pain
Modulation of Pain
Gate Control Theory: 1960, Ronald Melzack and Patrick Wall
Endogenous Pain Relief System
Revisited Gate Control Theory
Interneurons activated by fibres descending from PAG and associated areas
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