I have been baffled by this question for quite some time. It started when I read a lecture note stating the use of RC-circuit as an equivalent electrical system. It replaces the potential difference between the extra-cellular and intra-cellular fluid by a battery, the ion channel by a resistor, and the membrane by a capacitor. I have tried to make sense of that assumption but without any success. Is it me or something is wrong with that model?
Sounds reasonable to me, but since I am not familiar with biochemistry, I want to know the answer too.
Probably battery is for the different ion concentration of the fluids, resistor is for the current path through the ion chanels and capacitor for the membrane is for the limited but not neglectable concentration diference in and out. I guess that there is also internal electrical source, but it might be approximated via the battery and capacitor.
If you add the schematic(s) the question would be more understandable.
Hi Gashaw,
The "battery" you mentioned is the reversal potential of an specific ion yielded by the Nerst equation. The resistance (or conductance) is a quantitative measure of the ionic current flowing through the membrane. Finally, the capacitor represents the dielectric properties of the phospholipid bilayer (membrane) whose value is often referred as to 1uF/mm2
I hope this helps!
Hi,
If you need a good text book , I would advise you the axon guide available at : www.octopus.huji.ac.il/course/Links/Axon_Guide.pdf. (or at molecular devices)
That's really a "must have" to start with electrophysiology.
Regards
Thank you all. Erick, you pointed out a more realistic way of looking at it. Fabien, the reference looks quite interesting and thank you for that. I have downloaded it for further reading.
Something is wrong with every model. But for 99% of cases, when dealing with an isopotential sphere:
d[Vm]/dt = I/C
I = G * (Vm - Ve) works.
When it doesn't work, because you have very large differences in Ionic Concentrations, leading to rectifying currents, you have to use the GHK flux equation, which of course, has its own issues.
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