resting_action_pot

resting_action_pot - Lecture1...

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Lecture 1 I.  Principles of Membrane Excitability Eduardo Perozo 4-45 Jordan Hall 243-6580 eperozo@virginia.edu
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Outline Equivalent Electrical Circuit review of resting membrane potential passive membrane properties fundamentals of active signaling changes in ion conductance underlie changes in membrane potential The Action Potential action potential phenomenology voltage clamp analysis overview of Hodgkin & Huxley formalism
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Responses to Current Injection
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Electrochemical Driving Forces I = g ion *(V m -E ion ) there is a different driving force for each ion at any given Vm the same g for different ions can give very different current magnitude changes in g for a given ion will drive Vm toward the equilibrium potential for that particular ion
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Resting membrane potential so, E K ~ -100 mV and E Na is ~50 mV, but we know that membrane potential (Em) is usually somewhere in between (e.g. -75 mV). How can we get a stable Em of -75 mV? if Em is stable, then net current is 0, i.e., I K + I Na = 0: substitute: g K * (Em-E K ) + g Na * (E m -E Na ) = 0 solve for Em: Em = (E K * g K ) + (E Na * g Na ) g Na + g K the membrane potential is between E K and E Na , weighted by the relative membrane conductances for K + and Na + if gNa:gK = 1:5, then: Em = (-100 * 5) + (50 * 1) = -450 = -75 mV 5 + 1 6
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Equivalent electrical circuit model with unequal distribution of ions and differential resting conductances to those ions, we can use the Nernst equation and Ohm’s law in an equivalent circuit model to predict a stable resting membrane potential of -75 mV, as is seen in many cells NB, this is a steady state and not an equilibrium, since K + and Na + are not at their equilibrium potentials; there is a continuous flux of those ions at the resting membrane potential for resting Em = (E K * g K ) + (E Na * g Na ) + (E Cl * g Cl ) membrane potential g Na + g K + g Cl
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Passive membrane properties: capacitance capacitance (C) membranes act like capacitors they store charge and slow the kinetics of electrical signals specific capacitance for biological membranes is ~1 pF/cm 2 C = Q/V; 1/d C A, C
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resting_action_pot - Lecture1...

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