10 Pain - PAIN NEUROPHYSIOLOGY page 1 INTRODUCTION A Pain...

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PAIN NEUROPHYSIOLOGY A C Brown page 1 A6j INTRODUCTION A. Pain Vocabulary -algesia refers to pain hyperalgesia increased sensitivity to pain hypoalgesia decrease of pain sensitivity analgesia loss of or decrease in pain sensation neuralgia pain that follows the course of a nerve or is related to a nerve (e.g. trigeminal neuralgia) causalgia burning pain associated with previous tissue injury (sympathetic dystrophy) allodynia pain induced by an ordinarily non-painful stimulus hyperpathia combination of hyperalgesia and allodynia algesiometer device for generating quantitative pain stimulus dolorimeter device for generating quantitative pain stimulus B. Special Aspects of Pain Pain is a somatic sensation with many properties in common with other somatic sensations. However, pain has some unique aspects, among which are the following: 1. Wide variety of adequate stimuli 2. Subject to sensitization and self-reinforcement 3. Referred pain localization errors 4. Modulation or gating 5. Sensitization 6. Reflexes PAIN MODALITY and ADEQUATE STIMULI A. Distinct Modality (not extreme stimulation of other modalities) 1. Pain intensity can be reduced while other sensory modalities are maintained (analgesia without anesthesia) 2. Distinct afferent endings and pathways a. endings innervated by small axons: A- δ or C b. characteristics of endings 1) free nerve endings 2) widely distributed in throughout the body (skin, muscles, bones, joints, viscera, blood vessels) 3) high threshold 4) some respond to specific types of energy, others are polymodal (can be excited by several types of stimuli)
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PAIN NEUROPHYSIOLOGY A C Brown page 2 A6j PAIN MODALITY and ADEQUATE STIMULI B. Adequate stimulus: many 1. mechanical (tissue distortion) 2. thermal (Temperature > 45C, also cold) 3. caustic chemicals 4. inflammation 5. endogenous mediators (e.g. histamine, kinins) 6 metabolic byproducts (e.g. H + , K + ) 7. hypoxia; usually due to ischemia (e.g. angina, claudication)
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