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Question: QUESTION C:
For all the following questions, assume
RT / zF = 58 mV, and ignore any
contribution …


QUESTION C:

For all the following questions, assume
RT / zF = 58 mV, and ignore any
contribution by the Na/K pump.

The permeability ratio PNa : PK :
Cl of the neuron drawn below (at room temperature) is: 0.04 : 1 :
0.3.

Use the Goldman Equation to
calculate the resting membrane potential (RMP) of this neuron
[3].

     
Extracellular (mM)        
     Intracellular (mM)

Na+    40 4

K+ 6 200

Cl–         115
4

  

                                                                                               

2. If the permeability ratio of PNa :
PK rises to 25:1 during an action potential, calculate
the expected membrane potential at the peak of the action
potential. [3]

3. If extracellular sodium is reduced to 10 mM by
replacement with the impermeant ion choline,
calculate:

i) ENa  

ii)The resting membrane potential

iii)The expected membrane potential at the peak of the
action potential

4) Discuss how these new values compare
with those you obtained in 1. and 2.  

5) If during a voltage clamp experiment using an axon,
choline was used to reduce extracellular Na to lower it to 10 mM,
draw and label the currents you would expect to see during a
voltage step to 23 mV. [4]

N.B. Draw the voltage step and
be sure that your currents directly correspond to this
step.

6) Explain in your own words what membrane capacitance
is. [2 points]

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