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NB September 17th 2012.docx

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thSeptember 17 2012Cell PhysiologyLecture 4PRE NOTESAction Potentials at axon hillcok trigger zoneAll or none dont degrade over time once reach threshold Self propagating AP triggers next adjacent APVertebrate neurons get myelinIon entryelectroTONIC current spreadtriggering APMyelinFormed by glial cells shwann cells in PNS oligodendrocytes in CNSNodes of Ranvier exposed high density of voltage gated channels Where AP occursSaltatory conductioninsulationSaltatory conductionjumps from one node to another happens in insulated neuronsAP ModulationMax frequency is determined by the RELATIVE refractory period If the intensity of the signal is high enough you can still fire another signal you cant in absolute refractory periodAP vary in shape and speedbetween neuron types and btwn speciesWHAT CAN FACILITATE THIS MODULATION OF AP Voltagegated channels arent all built the sameNeurons dont all express the same panel of channelsQuantity of channels isnt constantDiversity in Signal ConductionIf many genes produce many channels a signal response will be different may open faster close faster etcK channels encoded by 18 genesproduce 50 DIFFERENT ISOFORMS11 isoforms of Na channels
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