Workout: The Nernst potential

Read

Nernst Potential

Launch

the simulation developed at the University or Arizona Nernst/Goldman Simulation.

Set up

Read the "Using the Simulator" page (under the heading "Help" on the left) to get some insight about how it works. Launch the simulator. You will get a window that looks like the figure at the right.

Answer these questions

1. Try changing some of the interior and exterior concentrations of the various ions using the sliders at the left. What is the difference between running the simulator using Nernst vs. Goldman? 

2. Run the Nernst simulator tab with Potassium ions (K⁺). Set the values of the ions to both be 100 mM inside (i) and outside (o) the cell. What value (E_k) do you get for the potential across the cell membrane? Is this what you expect? Why? Where are the extra + charges along the membrane? Where are the balancing - charges?

3. If you now decrease the concentration outside the cell to 10 mM, what happens to the membrane potential?

4. If you increase the temperature, does the membrane potential difference increase or decrease? Is this what you expect from the Nernst equation?

5. Why does the Nernst equation depend on temperature in that way? That is, what's the physics of the mechanism that produces this result?

Joe Redish Spring 2017