Measuring the Membrane Potential: Ohm’s Law
The intracellular and extracellular solutions in the body are ionic solutions,
and they will therefore conduct electricity. Membrane potentials are
voltages, which drive currents made up of the movement of ion species
such as Na+ and K+. Ions can cross membranes through ion channels. A
membrane containing these ion channels may represent a resistance in an
electrical circuit. The resistance may be made smaller the more channels
are open because ions then find it easier to pass through the membrane.
Georg Simon Ohm
Georg Simon Ohm was a German physicist and mathematician. As a school
teacher, Ohm began his research with the new electrochemical cell,
invented by Italian scientist Alessandro Volta. Using equipment of his own
creation, Ohm found that there is a direct proportionality between the
potential difference applied across a conductor and the resultant electric
current. This relationship is known as Ohm’s law. Ohm’s law can be used to
predict how much current would flow when the ion channels are opened, if
the membrane potential (voltage) and the resistance of the membrane to
Alessandro Volta
the passage of the ions are known.
V = I/R
V is voltage measured in volts
I is current measured in amperes
R is resistance measured in ohms
Voltage may be defined as the amount of potential energy between two points on a circuit.
One point has more charge than another. This difference in charge between the two points is
called voltage. It is measured in volts. Voltage is represented in equations and schematics by
the letter “V”.
Current is a measure of the amount of charge flowing through a circuit over a period of time.
Current is measured in amperes (amps) and is represented in equations and schematics by the
letter “I”.
Resistance is a measure of a material’s tendency to resist the flow of charge (current). It is
measured in ohms () and is represented in equations and schematics by the letter “R”.