Lecture 3 - current of potassium leaving the cell is equal...

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Lecture 3 None of the ions are in electrochemical equilibrium across the membrane. There can only be one membrane potential which is usually around -70 mV. Equilibrium potential: Na- 58 mV K+- -81 mV Cl-- -81mV All the time potassium leaves the cell, constantly All the time Sodium enters the cell A cell with both these conditions is in steady state When equilibrium potential is equal to membrane potential there is NO NET FLUX of potassium and a small net flux of sodium (ions). At -70 mV there is an efflux of potassium because it goes down its concentration gradient (125 M inside 5 M outside). At -70 mV there is a driving force into the cell for sodium and therefore there is an influx. When the membrane potential is more negative than the ion’s equilibrium potential there is an influx and when it is more positive there is an efflux. I ion = g ion ( E m- E ion ), where g= conductance and I=current For the membrane potential to be constant over time what needs to happen? Total current must equal 0 and therefore the current produced by sodium entering the cell and the
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Unformatted text preview: current of potassium leaving the cell is equal. There is an ohmic relationship with the cell, as the amplitude varies linearly with the voltage or potential of the membrane. With an action potential what happens is the permeability ratio is simply altered and that changes membrane potential! However, no matter what the membrane potential will never be equal to an ion’s equilibrium potential or the potential that the ion would be in equilibrium if it were the only permeant ion. Answers to in class questions a) depolarize b) hyperpolarize Gates When the gates are closed there is a low possibility/probability to find these gates open. During depolarization the permeability to sodium increases and b=20 which is 1,000 fold During repolarization the permeability to potassium increases The m-gate is known as the fast sodium channel and is one of the fastest biological actions known....
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This note was uploaded on 05/18/2008 for the course BIO 317 taught by Professor Simonhalegoua during the Fall '08 term at SUNY Stony Brook.

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