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Lecture 5

Lecture 5 - Fast Reflexes

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University of Toronto St. George
Human Biology
John Yeomans

HMB200H1S L5 Jan 24 2012biggest humanmammalian neurons 100micronsFast Reflexeseasy to seeFew synapsesSpeed and Timing in CNSNervous systems 100ms evolved because they are Compound Action Potentialfaster than hormonal systems 3ms chemical diffusionVoltagegated Na channelsAction potentials Axons fast myelinated A130msslow CReceptors fast ionotropic open in ms Gcoupledhormonalsteroidmediated minshrs flow thru membraneslow growth effectsCircuitsof synapsesprocessing at each synapse Simplestmonosynaptic stretch reflex w 2 neuronsCan slow down easilySlows info flow if more synapsesbut get more info to analyze getr more info out per unit timeFast systems w large neurons easiest to record from are the easiest to study Reflexes w giant FastSlow Receptorsneurons stSimple fnsescape reflexes 1 to evolveDirect feedback reflexesNeuronsBhvrLargest neurons Giant neuronsSingle synapses Squid or musclesSimple reflexes Spinal Cord or AplysiaFastestligand gatedNerve growth factorenzyme activates chemical reactiongrowth multiple effect mediated by kinase not gprotSteroid recs intracellular so steroid must get thru bilipid membraneCan regulate gene transcription ex primarysecondary sex characteristicsStarfish anemone fast response when touch armNeuronsBhvrwithdraw tentacles bring food in interactions btwn central visceraresponse tentaclesnot always avoidance sometimes approachfoodseekingSegmented animals w nerveselongated NS ganglia axonsWormtiny head ganglionbrainresponds to stimuli at front of animal have 3 giant axonsactivate fast escape response shrinking into hole by longitudinal axon from headtailAxonchain of cells linked work like linked act pot linked electricallySquidcompound cell that forms giant axon from assembled cells divided differently in squid than wormAplysiaa few ganglia in anterior endhead ganglia chain abdominal ganglion in centre w biggest cells can be identified easily poked coloured 1000 micron diameter neurons 10 times bigger than
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