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PAIN Dr Ghulam Mustafa LO’s of the class • • • • • • • • • Define pain Properties of pain Stimuli for pain Receptors for Pain Causes of pain Types of pain w.r.t., Site Fast vs Slow pain Pain pathways Body response to pain • Unpleasant sensory experience that is elicited by Noxious or nociceptive stimuli Properties of pain • Pain is a protective reflex • Pain receptors are widely distributed • Commonest symptom • Earliest sign of Morbidity • Non adaptive receptors • Certain viscera insensitive to pain – Brain – Liver parenchyma – Alveoli Stimuli for pain • Mechanical • Thermal – More than 45°C • Chemical – – – – – Bradykinin Serotonin Histamine Potassium ions Proteolytic enzymes Receptors for Pain 1. Superficial skin layers 2. Internal tissues • Periostium • Joint surfaces • Arterial walls • Falx and tentorium Causes of pain 1. Tissue damage • Bradykinin • Increased Potassium • Increased Proteolytic enzymes Rate of tissue damage α Pain intensity 2. Tissue Ischemia • Lactic acid by Anerobic metabolism • Bradykinin and proteolytic enzymes Causes of pain 3 Muscle spasm • Stimulate mechanosensitive pain receptors – Compress the blood vessels and cause ischemia – Increases the rate of metabolism Types of pain w.r.t., Site 1. Cutaneous pain • Skin and subcutaneous tissues • Accurately localized 2. Deep somatic pain • Muscles, Tendons, Joints, Ligaments • Mechanical forces, Ischemia, Chemicals 3. Visceral pain • Poorly localize, radiates or refers • Associated with ANS dysfunction • Rigidity & tenderness nearby skeletal muscles • Fast pain – – – – Sharp pain Pricking pain Acute pain Electric pain • Stimuli – Mechanical – Thermal – Electrical • Transmission – A Delta Fibres • Slow Pain – – – – Burning pain Ache Throbbing pain Chronic pain • Stimuli – Chemical • Transmission – Type C fibres • Transmission velocity – 6 to 30 m/s • Perception time – 0.1 sec after stimulation • Body parts involved – Usually skin • Duration – Short • Neurotransmitter – Glutamate • Transmission velocity – 0.5 to 2 m/s • Perception time – 1 sec or more • Body parts involved – Skin and deep tissues • Duration – Long • Neurotransmitter – Substance P • Localized • • • • • Examples of stimuli Needle prick Skin cut Burn Electric shock • Neo spino thalamic tract • Diffuse • Tissue destruction • Paleo spino thalamic tract • A Delta fibres • Terminate in Lamina I Lamina Marginalis • Excite 2nd order neurons • Cross to opp side thru Ant commissure • Pass upward in Anterolateral pathway • Type C fibres • Terminate in Lamina II & III substantia gelatinosa • Signals thru short fibre neurons • Reach Lamina V • Last neuron give rise to long axons • Cross to opp side thru Ant commissure • Pass upward in Anterolateral pathway • Neospinothalamic • Few – Reticular areas of brain stem • Most – Thalamus – Ventro basal complex – Post nuclear gp • Somatosensory cortex • Paleo spino thalamic – Reticular areas of medulla and pons – Tectal area of mesencephalon – Peri aqueductal gray region • From brain stem – Intra laminar nuclei – V/L Nuclei of thalamus – Hypothalamus Body response to pain • Motor reaction: – Withdrawl reflex – Muscle rigidity • Autonomic reaction – Mild pain • Posterior hypothalamic nuclei –Increased sympathetic discharge –Tachycardia –Increased Blood pressure • Severe pain • Anterior hypothalamic nuclei –Increased Para sympathetic discharge –Bradycardia –Decreased Blood pressure • Emotional reactions – Anxiety – Depression – Crying LO’s were • • • • • • • • • Define pain Properties of pain Stimuli for pain Receptors for Pain Causes of pain Types of pain w.r.t., Site Fast vs Slow pain Pain pathways Body response to pain