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NeuroLecture 2.docx

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University of Toronto St. George
Michelle French

Neuro:Lecture 2 October-28-12 12:30 AM Membrane most permeable to K+ at rest, but Na and Cl are also coming in and out So MP is -70 mV instead of -90 mV •Actual membrane potential can be calculated with an expanded Nernst equation which needs a term for each ion species •Goldman equation Na+ equilibrium potential •Sometimes Na can dominate permeability, causes drastic MP change •Then would have net Na+ current inward •At equilibrium there is a net cation accumulation inside the membrane •Membrane potential is positive with respoect to outsed o ENA+ = +60 mV Cl ions •Large proteins are trapped inside cell •These have negative charges, so Cl pushed out of te cell •NOT DUE TO ACTIVE PUMP Na+ channels •To generate a signal, membrane increases its conductance by opening a channel permeable only to Na+ ion •In normal resting MP this channel is shut (at -70 mV) •To open channel need to depolarize membrane ( to -55 mV) •HOWEVER, Na channel inactivation also takes place •To remove inactivation, MP needs to fall below threshold again Action potential •An impulse (short lived change in MP) used as a signal •Can only be produced in membrane of cells that have voltage gated Na channels •These are called excitable cells - have high density of Na channels • When ch
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