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Homework 2 key - Homework 2 1 You are studying a neuron...

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Homework 2 1) You are studying a neuron with the following concentrations of ions inside and outside of the cell: intracellular extracellular Sodium 50mM 150mM Potassium 100mM 10mM Chloride 5mM 120mM Enough organic anions are present inside and outside of the cell to provide electrical and osmotic neutrality. The cell is at room temperature. The permeability to sodium is 10, the permeability to potassium is 100, the permeability to chloride is 0 A) What is the membrane potential of this cell? B) Now you raise the extracellular potassium to 100mM. What is the new membrane potential? 58log((100X10 + 10X150)/(100X100 + 10X50)) = 58log(2500/10500) = -36.1mV 58log((100X100 + 10X150)/(100X100 + 10X50)) = 58log(11500/10500) = 2.29mV At +2.29mV all voltage gated sodium channels are inactivated, so no action potential fires. On a test, partial credit would be given for saying that the action potential would be small because the increase in membrane potential would decrease the driving force on sodium. C) What affect does the change in potassium concentration have on action potential firing?
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2) You discover that in the neuron you are studying (unlike in the squid giant axon) voltage gated potassium channels inactivate. The rate of inactivation of the voltage gated potassium channel is much slower than that of the voltage gated sodium channel. All other features of this channel are identical to those of the squid voltage gated potassium channel. A) Draw a graph of conductance versus time for this voltage gated potassium channel.
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