Measuring the Resting Membrane Potential
- In a resting axon, the distribution of cations and anions polarizes the plasma membrane. The intracellular fluid (ICF) becomes relatively negative to the extracellular fluid (ECF).
- A voltmeter is used to measure the charge difference (voltage or elec-trical potential) between the ECF and ICF. The greater the difference, the greater the voltage.
- Two electrodes are connected to the voltmeter. One serves as the ground electrode (reference electrode, indifference electrode) and the other is the recording electrode.
- The recording electrode typically consists of a glass tube filled with KCl solution and a silver wire coated with Ag/AgCl. The electrode is able to convert ionic current to electrical current, which is sent to the voltmeter.
- The ground electrode is placed outside the membrane and the recording electrode is inserted recording electrode into the axon.
- Charge differences between the ECF and ICF (resting membrane potential or RMP) are displayed in millivolts (mV) on the voltmeter.