Simulation of the Generation of an Equilibrium Potential

This simulation adds impermeable anions to the picture, and permits the voltage to change so that it reflects the imbalance in cation and anion concentrations. Click the mouse in one of the chambers to reset all the particles to that location. The strip chart at the bottom shows a history of the membrane potential as the cations diffuse to an electrochemical equilibrium.

Record the membrane potentials and number of cations that diffuse into the right-hand compartment, at several different internal ion concentrations. Click the mouse to switch all the particles to the other side of the membrane. Is there a pattern, that is, a correlation between the membrane potential and the cation gradient? Go on to the next page to examine this situation more carefully, but first consider the following questions.

  1. What would happen if there were anions and cations on both sides of the membrane?
  2. In what way are the imbalances illustrated here unrealistic? What might make the simulation more realistic?
  3. What do you think would happen if the membrane were equally permeable to both anions and cations. Suppose, instead, it had a permeability to anions about 10% of its permeability to cations.

Record your speculations for later consideration.