Electrical Currents

 

Electrophysiological equipment can also measure current, which is the flow of electrical charge passing a point per unit of time. Current (I) is measured in amperes (A).Usually, currents measured by electrophysiological equipment range from picoamperes to microamperes.

For instance, typically, 10up4 Na+ ions cross the membrane each millisecond that a single Na+ channel is open. This current equals 1.6 pA.

Two rules about currents often help to understand electrophysiological phenomena:

 

(1)current is conserved at a branch point I = Sum of I; and

(2)current always flows in a complete circuit.

 

In electrophysiological measurements, currents can flow through capacitors, resistors, ion channels, amplifiers, electrodes and other entities, but they always flow in complete circuits.