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Physio Unit 9 Items that directly increase chemical pain: Bradykinin, serotonin, histamine, K+, acid, proteolytic enzymes Which fibers localize a pain stimulus? Aδ pain fibers (almost all pain travels via anterolateral system) localizes pain with the help of the dorsal column-medial lemniscal system’s Aβ tactile receptors Aδ fibers on the anterolateral system synapse in lamina I Items that enhance sensitivity only to chemical pain only: Prostaglandins and substance P (P2—That’s the Party Posse!) Aβ tactile receptors (5) Meissner’s, Iggo dome (Merkel’s), hair receptors, pacinian, Ruffini’s (PHIRM Aβs) First synapse of epicritic system Dorsal/cuneate and gracile nuclei in the lower medulla; followed by decussation Protopathic / epicritic synonyms Protopathic = anterolateral system; epicritic = dorsal column-medial lemniscal Thalamic destinations of somatosensory pathways Protopathic => ventrobasal and intralaminar nuclei; epicritic => ventrobasal nucleus ONLY Additional destinations of anterolateral system Protopathic => spinoreticular tract & spinomesencephalic tract ( + spinothalamics above) Anterior/lateral white columns travel by anterior/lateral spinothalamic tracts Cortical entrance level Input to cortex: layer IV Asterogenesis = inability to judge neither shape nor form (bilateral destruction of somatosensory area 1) Amorphosynthesis = inability to recognize complex objects on the opposite side of the lesion from unilateral destruction of the somatosensory association area Weber-Fechner principle Discrimination ability of stimulus strength is proportional to the log of stimulus strength Purpose of corticofugal signals MODULATE sensory signals Decrease signal transmission when input intensity is too great They travel backwards from cortex to thalamus, medulla, and spinal cord Amplifying Divergence Example Characteristic of corticospinal pathway, which controls skeletal muscles Divergence into multiple tracts Occurs in information transmitted by dorsal column-medial lemniscal system Labelled line principle Only one modality of sensation is transmitted by a nerve fiber Accommodation of Receptors Lessening neuronal excitability due to: Progressive inactivation of sodium channels Decremental conduction Decrease in membrane potential as it spreads electrotonically to soma Strychnine inhibits action of glycine – therefore strychnine excites neurons Acidosis / alkalosis effects on CNS Alkalosis increases excitability => seizures; Acidosis depresses => comas Neuropeptides versus small-molecule transmiters (ACh, amines, amino acids, NO) Neuropeptides are produced in the soma and axonally streamed, more potent Possible Ionophore components (2, exclusive) Either an ion channel or second messenger activator