Webster_Ch4_HW_explained

Webster_Ch4_HW_explained - cathodal potential for current...

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Briefly discuss stimulation of an excitable cell (Webster problems 4.3 & 4.4 of homework set #3)
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Squid Axon - + cathode V Resting potential (Vm) of excitable cells anode Squid Axon - + cathode V anode V=-90mV-0mV V=-90mV Define: V=anode potential – cathode potential Remember: Vm=Vin-Vout=-90mV-0mV=-90mV V=0mV-(-90mV) V=+90mV Recording mode The sign of the recorded Vm depends upon placement of the anode!
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Squid Axon - + cathode During stimulation electrons flow from the cathode to the anode. Cations are positively charged. Anions are negatively charged. Cations move toward the cathode and the anions (e-) move toward the anode. e- i V Stimulation of excitable cells anode Current flows outward and the membrane depolarizes . Squid Axon - + cathode i e V anode Current flows inward and the membrane hyperpolarizes . Stimulating mode: anodal potential must be higher than
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Unformatted text preview: cathodal potential for current to flow. Positive values of V will make resting membrane potentia l less negative, causing depolarization. New Vm=-90mV+2mV=-88mV Positive values of V will make resting membrane potentia l more negative, causing hyperpolarization. New Vm=-90mV-2mV=-92mV 0mV 2mV-2mV 0mV Extracellular stimulation of excitable cells Hyperpolarization Depolarization i Extracellular stimulation of excitable cells i At time t1 a “cathodal” action potential is initiated by membrane depolarization caused by the stimulus. Anodal block : membrane hyperpolarization delays action potential initiation. At time t1+dt an “anodal” action potential is initiated by adjacent membrane activation currents (Na+ currents). #1 #2...
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This note was uploaded on 11/14/2011 for the course ECE 3820 taught by Professor Wang during the Fall '11 term at GWU.

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Webster_Ch4_HW_explained - cathodal potential for current...

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