Electrophysiology is the science and branch of physiology that pertains to the flow of ions in biological tissues and, in particular, to the electrical recording techniques that enable the measurement of this flow. These include so-called passive recording as well as the "voltage clamp" and "patch clamp" techniques, which "clamp" or maintain the cell potential at a level the experimenter may specify. This control is established using feedback through an operational amplifier circuit. Control of the membrane potential is most obviously of value in the study of voltage-gated ion channels, but also aids in characterizing conductance.
The most common electrophysiological recording techniques establish electrical contact with the inside of a cell or tissue with a "glass electrode." Such an electrode is fashioned by the experimenter from a fine glass tube of about 1 mm diameter, which is then pulled to an even finer (but still hollow) tip under heat and allowed to cool. This glass "micropipet" is then filled with a chloride-based salt solution, and a chloride-coated silver wire is inserted to establish an electrochemical junction with the pipet fluid and the tissue or cell into which the pipet is inserted (typically with the aid of a microscope and finely adjustable pipet holders, known as micromanipulators). The chloride-coated silver wire connects back to the amplifier. Classically, electrophysiologists watched biological currents on an oscilloscope and recorded them onto chart paper, but now the vast majority use computers.
Amperometry is another technique of electrophysiology, which uses a carbon electrode and is typically used to detect changes in the chemical composition of the biological solution being recorded from.