Voltage (electric potential difference) is a force that causes electrically charged particles to move between two points. Voltage is to the flow of electrically charged particles as pressure is to the flow of water. If the negative and positive poles of a battery are connected by a wire, an electric current will flow through the wire because there is a voltage difference between the two poles. This flow of electric current can be used to do work, just as a current of water can be used to do work.
In wires, electric current is carried by electrons, but in solutions and across cell membranes, electric current is carried by ions. The major ions that carry electric charges across the cell membranes of neurons are sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl–). Recall that ions with opposite charges attract one another and those with like charges repel one another. How do these basic principles of bioelectricity establish the resting potential of the neuronal cell membrane? And how is the flow of ions through membrane channels turned on and off to generate APs?