Neurophysiology of pain

the slides includes description of pain, its types, receptors, pathways and how it is modulated

1. Neurophysiology of Pain Dr. karishma R. Pandey Assistant professor Department of basic and clinical physiology

2. Topics What is pain? Types Receptors Stimulated by Pathways Visceral pain Referred pain Projected pain/ phantom pain Modulation

3. What is pain? Pain is an unpleasant experience associated with acute tissue damage . Experienced: following injury, organic diseases such as advanced cancer, its origin within the CNS itself (not associated with tissue damage) Accompanied by emotional reaction (fear or anxiety) 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.

4. Functions of Pain Protects body against further injury Guides functional recovery May enhance disability

5. Classification Fast Pain Slow Pain 2-5 micro met dia 0.4-1.2 miro met dia 12-30 m/s 0.5-2 m/s A fibre C fibre Monomodal Polymodal Activated by either high intensity mechanical stimuli or thermal stimuli(<5 C) Activated by high intensity mechanical, chemical and thermal (both hot and cold) stimuli Glutamate Substance P or CGRP Follow neospinothalamic tract Follow paleospinothalamic tract

6. Nociceptors Responsive to noxious/ painful stimuli Free nerve endings Non-adapting nature Stimuli Mechanical Thermal: <5 or >45 C Chemical

7. Receptors Vanilloid receptor-1 (VR1 ): Vanillins , capsaicin, protons and to potentially harmful temp >43 ° VRL-1: temp > 50 °

8. Organization of Spinal Cord

9. Anterolateral Pathway: Spinothalamic Pathway Sensations of pain, thermal and crude touch

10. Neospinothalamic Pathway: Fast Pain (More Localized)

11. Paleospinothalamic Pathway: Slow Pain (Less Localized) Diffuse projection to cerebral cortex and limbic system

12. 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 A δ 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

13. 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

14. Mechanism of Referred Pain

15. Projected Pain

16. Phantom Pain

17. Modulation of Pain Gate Control Theory: 1960, Ronald Melzack and Patrick Wall

18. Endogenous Pain Relief System

19. Revisited Gate Control Theory Interneurons activated by fibres descending from PAG and associated areas