This simulation will help you understand the Goldman equation and how it relates the permeability and resting potential of living cells.

In the lectures I told you that the upstroke of the action potential was due to an increase in the permeability of the membrane to Na⁺ which causes the membrane potential to move towards the equilibrium potential for Na⁺ which is about +65 mV. A more modest Na⁺ permeability of resting membranes also explains why the membrane potential of some cells is -70 and not -85 mV. Remember that the equilibrium potential for K⁺ is about -85 mV.

This behaviour cannot be explained by the Nernst equation but a modification of it can do just this. The modified equation is called the Goldman equation. I recommend that you read through these notes on the Goldman equation before running either of the simulations.

I used the Goldman simulator in lectures to illustrate the Goldman equation and the way in which the increase in Na⁺ permeability underlies the action potential upstroke. Try it and see if things become clearer. You should take time to discuss what you see with your colleagues.

These questions are for your benefit. Your attempts here are not being monitored or assessed (your end of year exam will do that). We hope that this opportunity to test your knowledge will lead you to a better and deeper understanding of this important area of Physiology.