<p>Most neurophysiological recordings use <a href="https://en.wikipedia.org/wiki/Silver_chloride_electrode" rel="nofollow noreferrer">silver/silver chloride contacts</a>; 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.</p>
<p>Of course, silver isn't participating in the actual biology of producing action potentials, it's just in the electrode doing the measuring.</p>

CC BY-SA 4.0
2022-03-11T22:04:33.307Z
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?
orjün
CC BY-SA 4.0
2022-03-11T22:05:38.007Z
@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.
Bryan Krause
CC BY-SA 4.0
2022-03-11T22:06:41.533Z
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).
orjün
CC BY-SA 4.0
2022-03-11T22:09:01.640Z
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 :)
Bryan Krause
CC BY-SA 4.0
2022-03-11T22:10:07.097Z
Be vary wary of thinking too much about concentration changes in neuroscience...concentration changes are miniscule. Membrane permeability changes are large.
Bryan Krause
CC BY-SA 4.0
2022-03-14T14:44:26.530Z
Got it. What do you think of this logic (part I):

Let's say we have a neuron, a silver electrode "pretty" close to it, and an extracellular fluid that doesn't not disrupt the normal mechanics of action potential propagation.

The moment I place in the electrode (even before hooking up the ground), there's an equilibrium established between solid and aqueous silver (though no current is generated). The moment I hook up the ground (which is also a silver electrode—but placed intracellularly with respect of the neuron), a current is generated (due to the existence of a differential
orjün
CC BY-SA 4.0
2022-03-14T15:47:39.143Z
(part II) membrane potential. This is my justification: let's say we'd placed the ground and the active silver electrode in two separated solutions with the same net charge (0 for each, if you will). We likely are not going to get a current across the electrodes. Now, let's say I somehow create a differential net charge between the two solutions (solution A is, for example, more negatively charged compared to solution B). Now, solution A can "accommodate" more silver ions (positively charged) compared to solution B.
orjün
CC BY-SA 4.0
2022-03-14T15:58:09.043Z
(part III) This means that, as long as that net charge exists (and other factors too, but for the sake of simplicity), there's a net movement of electrons between the electrodes (aka current). 

A similar situation exists in the case with the neuron and the electrode. There's a voltage difference across the neuron membrane, which affects the equilibrium of silver ions at the two electrodes. During an action potential (or any membrane voltage change), the disturbance is similarly propagated to the equilibrium of the silver ions. 

What do you think of that logic/explanation?
orjün
CC BY-SA 4.0
2022-03-14T15:59:08.060Z
(part IV). Followup question: in the situation with the neuron, are we ever worried that the concentration of aqueous silver might be depleted (as in, all aqueous silver converting to solid silver) at one or both of the electrodes?
orjün
CC BY-SA 4.0
2022-03-14T16:16:54.187Z
@orjün The comments section isn't meant to be used for further questions. There's really no biology in what you are asking about, this is just basic electrochemisty; I think you could ask about these things in physics or chemistry. As far as worrying about the electrodes...theoretically no, that would never happen. Practically yes, electrodes go "bad" over time and need to be re-coated when you use them day after day; I'm not sure what the chemistry is behind that, though, I suspect it's due to deposition of other chemical species. For long-term in vivo recording, other problems happen first.
Bryan Krause
CC BY-SA 4.0
2022-03-11T21:42:22.183Z
2022-03-11T21:42:22.183Z
Bryan Krause
<p>Thank you for reading this.</p>
<p>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).</p>
<p>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.</p>
<p>What's the &quot;parallel&quot; situation in measuring spike activity? Consider the following diagram:</p>
<p><a href="https://i.sstatic.net/VxxeG.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/VxxeG.jpg" alt="enter image description here" /></a></p>
<p>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?</p>
<p>Thank you.</p>

<neuroscience><electrophysiology>
Measuring spike activity with an electrode: using the principles present in galvanic cells, can one explain how current flows in the electrode system?
orjün
# Measuring spike activity with an electrode: using the principles present in galvanic cells, can one explain how current flows in the electrode system?

(Asked by: username_0 on 2022-03-11)

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](https://i.sstatic.net/VxxeG.jpg)](https://i.sstatic.net/VxxeG.jpg)

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.

**Tags:** neuroscience, electrophysiology


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## 1 answers

### Answer by username_1 on 2022-03-11. Score: 1

Most neurophysiological recordings use [silver/silver chloride contacts](https://en.wikipedia.org/wiki/Silver_chloride_electrode); 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.

> **Comments:**
> **username_0**: 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?  
> **username_1**: @username_0 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.  
> **username_0**: 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).  
> **username_1**: 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 :)  
> **username_1**: Be vary wary of thinking too much about concentration changes in neuroscience...concentration changes are miniscule. Membrane permeability changes are large.  
> **username_0**: Got it. What do you think of this logic (part I):  Let's say we have a neuron, a silver electrode "pretty" close to it, and an extracellular fluid that doesn't not disrupt the normal mechanics of action potential propagation.  The moment I place in the electrode (even before hooking up the ground), there's an equilibrium established between solid and aqueous silver (though no current is generated). The moment I hook up the ground (which is also a silver electrode—but placed intracellularly with respect of the neuron), a current is generated (due to the existence of a differential  
> **username_0**: (part II) membrane potential. This is my justification: let's say we'd placed the ground and the active silver electrode in two separated solutions with the same net charge (0 for each, if you will). We likely are not going to get a current across the electrodes. Now, let's say I somehow create a differential net charge between the two solutions (solution A is, for example, more negatively charged compared to solution B). Now, solution A can "accommodate" more silver ions (positively charged) compared to solution B.  
> **username_0**: (part III) This means that, as long as that net charge exists (and other factors too, but for the sake of simplicity), there's a net movement of electrons between the electrodes (aka current).   A similar situation exists in the case with the neuron and the electrode. There's a voltage difference across the neuron membrane, which affects the equilibrium of silver ions at the two electrodes. During an action potential (or any membrane voltage change), the disturbance is similarly propagated to the equilibrium of the silver ions.   What do you think of that logic/explanation?  
> **username_0**: (part IV). Followup question: in the situation with the neuron, are we ever worried that the concentration of aqueous silver might be depleted (as in, all aqueous silver converting to solid silver) at one or both of the electrodes?  
> **username_1**: @username_0 The comments section isn't meant to be used for further questions. There's really no biology in what you are asking about, this is just basic electrochemisty; I think you could ask about these things in physics or chemistry. As far as worrying about the electrodes...theoretically no, that would never happen. Practically yes, electrodes go "bad" over time and need to be re-coated when you use them day after day; I'm not sure what the chemistry is behind that, though, I suspect it's due to deposition of other chemical species. For long-term in vivo recording, other problems happen first.  

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