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PAIN MODULATION Prof. Ashraf Husain MODULATION • Pain modulation means pain perception variability which is influenced by endogenous and exogenous mechanism 3 Referral of pain from the internal organs Organ Site of reffered pain • Meninges • Heart Back of head and neck Central chest arms (usually left), neck, occasionally abdomen. Behind sternum Shoulder tip Behind sternum Cont…5 • Trachea • Diaphragm • Oesophagus Organ Site of reffered pain • Stomach, duodenum Upper abdomen, epigastrium • Small bowel, pancreas Around umbilicus • Large bowel, bladder Lower abdomen above pubic bone 6 VISCERAL PAIN 7 VISCERAL PAIN PATHWAY Pain - Aδ and fibers Travel with autonomic afferent Spinal cord (Dorsal Horn) Lat. spinothalamic tract Thalamus Somatosensory Cortex 8 CHARACTERSITICS OF VISCERAL PAIN • 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 9 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 SPINAL MODULATION A MODAL OF “GATING” OF PAIN 12 SPINAL MODULATION DORSAL HORN GATING MECHANISM 13 ASCENDING AND DESCENDING PAIN PATHWAYS 14 SUPRASPINAL MODULATION Descending Analgesic Pathway 15 SUPRASPINAL MODULATION OPIOID RECEPTOR MODULATION Neurotransmitters in Analgesic Pathway 17 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. 18 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 20 and diabetic neuropathy. 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 TERMS FREQUENTLY USED • 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. 23 TERMS FREQUENTLY USED Thalamic Syndrome .Obstruction of the thalmogeniculate branch of the posterior cerebral artery Affects posterior thalamic nuclei. . Prolonged severe pain. 24 TERMS FREQUENTLY USED 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 25 SITES & MECHANISM OF PAIN RELIEF 26 Trans Coetaneous Electrical Nerve Stimulation (TENS) 27 28