PAIN MODULATION Prof. Ashraf Husain

MODULATION Pain modulation means pain perception variability which is influenced by endogenous and exogenous mechanism 3

5 Referral of pain from the internal organs MeningesBack of head and neck HeartCentral chest arms (usually left), neck, occasionally abdomen. TracheaBehind sternum DiaphragmShoulder tip OesophagusBehind sternum Cont… OrganSite of reffered pain

6 Stomach, duodenumUpper abdomen, epigastrium Small bowel, pancreasAround umbilicus Large bowel, bladderLower abdomen above pubic bone OrganSite of reffered pain

7 VISCERAL PAIN

8 VISCERAL PAIN PATHWAY Pain - Aδ and fibers Travel with autonomic afferent Spinal cord (Dorsal Horn) Lat. spinothalamic tract Thalamus Somatosensory Cortex

9 Poorly localized Associated with nausea and autonomic disturbance Often referred to another part of the body Cutting, crushing are not painful when applied to viscera Pain is caused by distension, ischemia and inflammation CHARACTERSITICS OF VISCERAL PAIN

MODULATION Pain modulation means pain perception variability which is influenced by endogenous and exogenous mechanism 10

Pain modulation can be discussed under following headings –Spinal modulation of pain input Gate theory of pain –Supra spinal modulation Role of periaqueductal grey (PAG) matter Role of Nucleus Raphe Magnus (NRM) –Pain modulation by use of Opioid neurotransmitters eg: endorphin, enkaphalin Dynorphin. 11

12 A MODAL OF “GATING” OF PAIN SPINAL MODULATION

13 DORSAL HORN GATING MECHANISM SPINAL MODULATION

14 ASCENDING AND DESCENDING PAIN PATHWAYS

15 Descending Analgesic Pathway SUPRASPINAL MODULATION

17 Neurotransmitters in Analgesic Pathway OPIOID RECEPTOR MODULATION

18 MECHANISM OF OPIOID NEUROTRANSMITTER ACTION: ENDORPHIN: Neurons using endorphin or enkaphalin are found in PAG where they inhibit GABAnergic interneurons that normally suppress the anti-nociceptor neurons ENKAPHALIN: It is used by interneurons in lamina II responsible for inhibiting the lamina – I nocioceptor-specific spinothalamic neurons ENDOGENOUS MORPHIN: It has been identified in terminals forming synapses with neuron having μ-opioid receptors in pain modulating pathways.

Chronic Pain Chronic pain can be considered as bad pain because it persist long after injury and is often refractory to pain killers. Chronic pain caused by nerve injury is called neuropathic pain. 19

Neuropathic pain Caused by the damage to peripheral nerve ( adrenalin release by sympathetic discharge) The distal cut end develops a scar tissue forming rounded ball ( neuroma) which is sensitive to pressure. Repeated activation causes continuous pain. Examples are like, post herpetic neuralgia and diabetic neuropathy. 20

Phantom pain Pain felt in an amputated part long after amputation was done. Many explanations are given to explain this phenomenon. 21

Stress induced analgesia It’s a well known phenomenon seen when the soldier is wounded in battle field but feels no pain until the battle is over. The cause is not known may be it is similar to Gate control hypothesis. 22

23 Hyperalgesia: Excessive Pain Allodynia: Pain caused by any other sensation e.g. touch will cause pain. Muscular Pain: Less blood flow in the muscles (ischemia). Stress analgesia: Mild degree of pain is not felt if the other part of the body has excessive pain. Causalgia: Burning pain. TERMS FREQUENTLY USED

24 Thalamic Syndrome.Obstruction of the thalmogeniculate branch of the posterior cerebral artery Affects posterior thalamic nuclei.. Prolonged severe pain. TERMS FREQUENTLY USED

25 TRIGEMINAL NEURALGIA It is excruciating intermittent pain by stimulation of trigger area in the face as for eg. Washing of face, combing hair, blast of air on face. It results from compression of trigeminal nerve root by blood vessels TERMS FREQUENTLY USED

26 SITES & MECHANISM OF PAIN RELIEF

27 Trans Coetaneous Electrical Nerve Stimulation (TENS)

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