Basic Electrophysiology
In a cell, the basic circuit that was discussed in the first section is set up by the membrane and the unequal distribution of ions on either side of it.
How does this produce a voltage, resistance and current? Suppose you set up the beaker below with a 150 mM solution of KCl on one side, a 15 mM solution of KCl on the other, and an impermeable barrier between them.
Since there is a higher concentration of KCl on the left side, there is a strong chemical driving force for the K+ and Cl- to move to the right. But since there is an impermeable barrier, no ions can cross. For this reason, the voltmeter at the top of the figure reads zero; on each side, there are as many positive charges as negative, so they cancel each other out.