BIOE 201 - NERNST STUDY QUESTIONS
5 January 2004
The next questions refer to a cell, in a dish of physiological saline at 37°C with the
following properties:
Solute
Na+
Outside Cell
Inside Cell
145
mM/L
12
mM/L
K+
4
mM/L
155
mM/L
Cl–
120
mM/L
4
mM/L
A–
0
mM/L
155
mM/L
Membrane Potential = –90mV
Size of cell: 10um x 10um x 100um rectangular solid
Membrane capacitance = 1 uF/cm**2
1. Please fill in the table below on the size of the Nernst potential for that solute and
direction of trans-membrane flux:
Solute
Nernst Potential
Direction of Flux
Na+
K+
Cl–
A–
Please Note: other cells and conditions will use the same equation to solve the same
type of problem, but will not have the exact same concentrations. Focus on
understanding the use of the Nernst potential and Ohm’s law to make
BIOE201B (2004) NERNST WORKSHEET
PAGE 2
predictions of this sort, not just on what answers fit the boxes in this particular
case.
BIOE201B (2004) NERNST WORKSHEET
PAGE 3
2. Given the knowledge that there are two major species setting the membrane
potential, please write an equation that would allow you to predict the membrane
potential, given the ratio of the conductances:
Please use this equation to predict the membrane potential if the ratio of sodium
conductance to potassium conductance were 0.05:
Please use this equation to predict the membrane potential if the ratio of sodium
conductance to potassium conductance were 20:
3. Now revise the above equation to add in Chloride conductance.
Please calculate the effect that this has on the predicted resting potential of the cell if
the ratio of chloride conductance to potassium conductance is 0.02:
Suddenly, there is a shunting inhibitory synapse fired on the cell, making the
chloride conductance increase 50-fold. What is the effect of this synapse opening on
the cell if it is otherwise at rest:
What would be the effect of the same inhibitory synapse firing be on the membrane
potential if the cell were in the midst of an action potential with the ratio of sodium
conductance to potassium conductance of 20: