# Animal Physiology-Membrane Potential

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Intracellular Extracellular
Na+ 12 mM 160 mM
Cl- 7 mM 110 mM
K+ 140 mM 5 mM

1.How do you calculate the equilibrium potential for potassium, K+, under these conditions?

2. Assuming that Na+ is the only ion the plasma membrane of this cell is permeable to, at what voltage will there be no net flux of any ions? Can you give the equation along with how you go about it?

3.Can you calculate (predict) the resting Vm for a neuron with these ion concentrations above (at 37°C). Assume now that the membrane is 20x more permeable to K+ than to Na+, and 100x more permeable to K+ than to Cl-. Again with the equation first.

4. Why is the Vm of this neuron, calculated in #3, closer to EK+, than to ENa+?

5. Assume now that the plasma membrane of this neuron undergoes a rapid change in ion permeability so that it is now 20x more permeable to Na+ than to K+, and 100x more permeable to Na+ than to Cl-. Predict (calculate) the membrane potential under these conditions. Again with the equation first.

I don't know how to do these problems. I need help severly!

• Animal Physiology-Membrane Potential -

For #1, I got E(K+) = 60/+1 * log (5mM/140mM) = -87mV I think this is right but I don't the rest

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