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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:

enter image description here

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.

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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.

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  • $\begingroup$ Thanks for the comment. Follow up: I'm trying to imagine how fluctuations in Na+ concentrations (as one might see during action potential propagation) might influence the oxidation/reduction of sliver/sliver chloride. Let's say we got an electrode right next to an axon. Ag(s) in that electrode is in an equilibrium with Ag(aq). How do changes in Na+ concentration affect that equilibrium? Is it perhaps that the electrical interactions between Na+ and Ag2+ affect the availability of Ag(aq) at the electrode site? $\endgroup$
    – orjün
    Mar 11, 2022 at 22:04
  • $\begingroup$ @orjün It's not a change in sodium concentration that's important, it's a change in voltage. The ions in the solution in the vicinity of the silver wire are behaving much like the electrons in a conductive metal. $\endgroup$
    – Bryan Krause
    Mar 11, 2022 at 22:05
  • $\begingroup$ Yes, but the change in voltage is largely as a result of change in sodium concentrations. Please let me know if I'm wrong (I also edited my previous comment). $\endgroup$
    – orjün
    Mar 11, 2022 at 22:06
  • $\begingroup$ Yes, though the silver electrode may see no sodium ions at all. A traditional patch clamp solution doesn't contain any sodium at all (though modern ones do; mine always had a little bit). I'd recommend forgetting about the electrode for a moment (because that's only really relevant to measurement) and first think about just how the voltage comes about. Then you can go back to chemistry to understand how the electrode does the sensing. It's unimportant for the biology which ordinarily needs to operate without anyone measuring from above :) $\endgroup$
    – Bryan Krause
    Mar 11, 2022 at 22:09
  • $\begingroup$ Be vary wary of thinking too much about concentration changes in neuroscience...concentration changes are miniscule. Membrane permeability changes are large. $\endgroup$
    – Bryan Krause
    Mar 11, 2022 at 22:10

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