Talk:Electrical properties of cell membranes

Overall, this entry is useful and well presented. The presentation and descriptions of the equations are particularly well done.

In the text, I made several changes in wording to make comprehension easier; these were not intended to change to content of the text.

Thank you for the useful comments.

I have three fairly minor comments for the author:

1) You begin with: "Like all cells, neurons are surrounded by a cell membrane." This article is entitled "Electrical properties of cell membranes", and thus should be generally about all cells. If you want to focus on neurons, you can mention that the function of neurons is especially tied to the electrical properties of its membrane, and thus neural membranes have been the most extensively studied for elucidating membrane properties, or something like that. But just keep in mind, throughout the text, that this is supposed to be about "cells" and not specifically "neurons".

Good point. I changed the text in several places to take this into account.

2) Under "Conductance", when you say there are ion channels, you refer directly to "Gating currents", implying that they are of significant importance to understanding ion channels . To my knowledge, gating currents are a small, transient effect of the movement of the voltage sensor, and are not tied to the main function of the ion channel, which is to conduct ionic charges. I would remove your reference; it is misleading as is.

Another good point. Link was removed.

3)At the end of your article you have a small section "Interactions in space". I would add a second section "Interactions in time". It could read something like this: This discussion of ion conductances in a patch of membrane has considered time-independent conductances and the membrane voltage at equilibrium. Cell membranes, such as those of neurons, can have constantly changing voltages, with currents turning on and turning off to precisely shape the activity of the cell. Such temporal changes in voltage are the basis of cellular electrical communication and are addressed in the section "Excitability".

I may be missing something here but there is already a section on "Interactions in time", it is the one immediately preceding the one on "Interactions in space" (the latter being essentially a pointer to the Cable Theory entry; see below for a comment) and it is entitled "Membrane patch: temporal dynamics". I have expanded the latter a little bit and now mention specifically excitability with a link to this entry (or at least what I expect will be in it). I also added how synapses fit in this picture.

>>> Sorry, I wasn't clear in my comments. What I felt was missing was a mention of voltage-gated conductances and their temporal dynamics. I see that you have now mentioned them.

>>> However, before you mention them, you say "There are many other currents, in addition to the sodium and potassium currents of the 'Hodgkin-Huxley' type discussed above..." To my knowledge, "Hodgkin-Huxley" type refers to the voltage- and time-dependence of the conductances; from what I can tell, these dynamics have not yet been mentioned in the article.

>>>I have modified this section slightly to make it more clear. See what you think.

It's good! I only made two small changes: (a) as it stood, it applied only to chemical synapses, so I added a sentence to included electrical synapses, too. (b) If a neurotransmitter opens channels, it definitely increases the conductance but it does not always make a current flow (not if the transmembrane voltage is at the reversal potential of this channel), so I removed a few words that implied the latter.

I know it is nitpicking...

A note on why there is the pointer to Cable Theory: all the material on this page was originally part of the Cable Theory page but I was asked to take it out there and make it a separate scholarpedia page such that Cable Theory only focuses on the spatial aspects.

>>> This seems wise. This topic is important enough to deserve its own section.

>>> Other than the minor modifications about Hodgkin-Huxley currents, I think this article is ready.

>>>>>>>>> FINAL COMMENTS: I changed "current" to "conductance" in a few places to keep our terminology consistent. I'm done nitpicking now!<<<<<<<<<

Great, are you ready to pull the trigger! This has been very useful, thanks again for the careful editing.

User 3: Equation 12

Dear curator,

thank you for your very didactic article, I ejoyed reading it. I found however an errata in the equation (12)

I cite: "From eqs. 5, 7, 10 and 11, we have the following Ordinary Differential Equation for the membrane voltage:

C\frac{dV}{dt} = g_{Na}(V_{Na}-V)+g_{K}(V_{K}-V) "

It should be "from eqs. 6, 7, 10 and 11".

The another errata is the sign convention. If you take the equations 10 and 11 and combine them, the sign of equation 12 should be opposite.

As a suggestion, maybe you can link in the "ses also" section the article "Conductance based models" of scholarpedia since it is closely related to this article.

Thank you again for your work.

Best

Alexandre Wagemakers

Author :

Good comments! I rewrote the first part of the temporal dynamics section, I hope it is clearer now. I also added the link to the Scholarpedia article.

Thanks for the careful reading!

--en