Measuring spike activity with an electrode: using the principles present in galvanic cells, can one explain how current flows in the electrode system?

Question

Thank you for reading this.

In a galvanic cell setup and around each electrode in that setup, we have species that either undergo oxidation or reduction—resulting in the literal flow of electrons between the two electrodes. We can then use a voltmeter to calculate the electric potential difference between the two electrodes (using Ohm's law).

A similar situation also happens when we're doing voltammetry—fast scan or otherwise. The typical example is of dopamine. One electrode is placed in the solution containing dopamine. The other electrode can be electronically manipulated to create a certain potential difference between itself and the electrode submerged in the dopamine solution. At some point across this voltage manipulation, dopamine is oxidized to dopamine-o-quinone. There's a literal flow of electrons (two per dopamine oxidized) which then establishes a current—which then we can measure.

What's the "parallel" situation in measuring spike activity? Consider the following diagram:

What species (if any) are oxidized to provide the electrons needed to establish a current in the electrode system (which then can be used to calculate the voltage difference across the axonal membrane)? During the propagation of an action potential—where voltage gated sodium channels open—what species (again, if any) are oxidized?

Thank you.

Answer 1

Most neurophysiological recordings use silver/silver chloride contacts; silver metal is being oxidized or silver chloride being reduced. Whichever occurs at the recording site, the opposite reaction is happening at the ground/reference contact.

Of course, silver isn't participating in the actual biology of producing action potentials, it's just in the electrode doing the measuring.