Talk:Membrane potential

message: * I have merged the contents from the article "Transmembrane potential" into this article and transformed the former in a redirect. I suggest that this article - "transmembrane potential difference" -  is moved to membrane potential, currently existing as a redirect, as "membrane potential" is the most often used term and as far as I know, it denotes the same. --Eleassar777 13:22, 14 May 2005 (UTC)
thread_title: Requested move

message: If you set dt=0 in the equation for capacitive current, then it doesn't eliminate the time dependance. Rather it gives an infinite capacitve current. You are dividing by 0. Maybe you mean to approximate the derivative by the differential dV/dt ~= deltaV=0.1V.
:Which still makes no sense.  There should clearly be an estimate of the time involved.Peiter 13:59, 21 December 2006 (UTC)
thread_title: dt=0

message: I cut all of the following text from the original article.  Basically there were several, well not factual errors exactly, but enough factual ambiguities, that I found it easier to re-write it from scratch.  I kept the text below in case anyone objects and wants to talk about reinstating some of it.
Cells are surrounded by a plasma membrane, which defines their extent and acts as a barrier between the cells and their external environment, for example interstitial fluid or blood plasma. The membrane, as a result of its lipid bilayer structure and specific membrane proteins, is selectively permeable (the hydrophobic interior prevents the passage of both large polar molecules and ions) and therefore will only allow certain species through. This selective permeability allows asymmetric concentrations of ions to exist between the intra- and extracellular fluids. These differences can be chemical or electrical (i.e. the difference in charge between the inside and outside). Most cells maintain a “membrane potential” of around –80mV relative to the surrounding fluid. The membrane potential is negative because usually cells have a net negative charge due to leakiness of potassium channels and the large size of negatively charged macromolecules such as proteins and RNA.
In animal cells, passive ion movement accounts for the majority of the electrical potential across the plasma membrane. This passive ion movement mostly consists of K+ ions. A  helps maintain an osmotic balance by keeping the concentration of intracellular Na+ low. Because the concentration of Na+ is so low inside the cell, other cations must be present to balance the negative charge carried by the cell's fixed protein anions. This balancing act is largely performed by K+ which is pumped in through the Na+/K+ pump and is also free to leave or enter the cell through the K+ leak channels. There is an electrostatic attraction for K+ due to the protein anions. This attraction balances against the tendency of K+ to diffuse out of the cell, down its concentration gradient, and it is these combined actions that create the membrane potential.
This can also be explained in the following way. Suppose that a cell initially has a membrane potential of zero – i.e. has no voltage gradient across the plasma membrane. However, the concentration of K+ inside the cell is higher than outside and so K+ will tend to leave the cell, driven by the concentration gradient. As it leaves the cell, the K+ leaves an unbalanced electrical charge. This creates a negative electrical charge, which is the membrane potential. The electrical field also opposes any further K+ leaving the cell. The membrane potential also tends to keep anions like Cl- out of the cell because their charge is also negative.
The cytosol, or interior, of a cell possesses a uniform electric potential or voltage compared to the extracellular solution. This voltage is the resting cell potential, also sometimes called the transmembrane potential of the resting cell. As an example, retinal ganglion cells have a resting cell potential of about -60 mV. Cells whose voltage is more negative than typical are said to be hyperpolarized, and those more positive are said to be depolarized. Healthy cells do not naturally hyperpolarize or depolarize except for brief intervals, for example during a nerve impulse or action potential. Among other roles, the cell potential acts as a reservoir for metabolic energy, which cells use to drive the transport of solute molecules across the membrane, to communicate with other cells and to trigger intracellular events.
Between the inside and outside of the cell (which is typically uniform electrically like the cytosol) the voltage rises very steeply just at the boundary created by the membrane. This create an electric field across the membrane, which exerts a force on ions and controls voltage-gated ion channels. Integral membrane proteins  such as channels, pumps, and exchangers establish the membrane potential by transporting specific ions in or out. In essence, resting cells are negative because positively charged potassium ions, which are more concentrated inside than outside, are allowed to leak out. The resulting negative voltage difference between inside and out is therefore approximately equal to the reversal potential for potassium. Sodium-potassium exchangers maintain intracellular potassium at a high concentration while pumping sodium into the extracellular solution, where the concentration of sodium typically is high.
The Goldman equation can be used to calculate the membrane potential given the concentration of ions on either side of the membrane and their permeability.
Synaptidude 8 July 2005 22:17 (UTC)
I am a beginner student of membrane potential physiology and this removed text answered (mostly) the following questions I had more effectively then the article in its current form does:
1) What is the reason Na+ stays at its location right across the barrier on the extracellular side of the membrane? Diffusion? Electrochemical potential? Electric Charge repulsion?
2) If the answer is the electrochemical gradient/potential, because it is trying to move to a "less" positive potential.. if its located extracellularlly isn't that the "great unknown" where any molecules/cells/protein etc. are able to float by and possibly influence it? What happens if one of these has a "LESS" positive potential then the membrane that Na+ is currently attracted?
3) Can someone explain why can't Na+ be used for the entire process to establish the same voltage interactions leading from resting to action potential (as long as thier was less concentration intracellularly... if it is about LESS positivity ..Or vice versa for K+?)?  — Preceding unsigned comment added by Spiked415 (talk • contribs) 15:39, 4 June 2012 (UTC)
thread_title: prior texts still to be edited and incorperated

message: There is a distinct article on resting potential. Maybe the bit about resting potential here can be moved to there? I'd do it, if I wasn't very busy with dutch wikipedia. Methoxyroxy 12:37, 2 November 2006 (UTC)
thread_title:  Merge? 

message: I'm finally more or less conviced and the article is mainly right (although the writing could be improved but that's not uncommon in wikipedian topics about chemistry). Maybe it should be noted that (i find that a bit esoteric) although there is an electric potential across the membrane there is no actual measurable difference in the global concentration of positive and negative ions across the membrane, that is, there is no actual charge excess in either size. That's because the effect of charge is hugely greater that the effect of concentration so an undetectable change in concentration creates a great change on electric potential. Knights who say ni 01:45, 24 November 2006 (UTC)
thread_title:  expert tag off 

message: It says "The typical membrane potential of a cell arises from the separation of potassium ions from intracellular immobile anions across the membrane of the cell." Isn't this a big mistake? The sodium-potassium pumps move sodium out of the cell and potassium in. True that the large anions (mainly proteins) are stuck inside the cell, but potassium ions are not separated from these anions--potassium is more concentrated on the inside of the cell than the outside. Should "sodium" simply be substituted for "potassium" in this sentence? I'm going to change it, and someone can "fix" it if they see this as a problem. Provophys 20:39, 26 July 2007 (UTC)
thread_title:  Big mistake? 

message: This is a nice article, informative and well worded. Just wanted to say thanks to the peepz involved. Ft. Jack Hackett (talk)  —Preceding comment was added at 21:41, 3 June 2008 (UTC)
thread_title:  Thank you 

message: No body really addresses what the membrane potential is, other times, like the first sentence in this article, it uses such a high level of language, no average person can understand it. Is the membrane potential the voltage of the cell's membrane, or is it a difference of the outside voltage-inside voltage? I don't like when people use phrases like "across membrane" or "against concentration gradient", if you're not familiar with this field, you won't understand what it means. Paskari (talk) 20:34, 5 August 2008 (UTC)
thread_title: What is the membrane potential

message: There are three articles now which discuss very much the same things with numerous repetitions and description of the same material in different terms.
*Resting potential
*Membrane potential
*Action potential
As it was already suggested by Methoxyroxy 12:37, 2 November 2006 (UTC)
replies: text: I will be happy to do that when you are ready.  I agree with you that these article need a lot of clean-up.  Action potential was once a featured article, but it has become far too long and poorly organized.  One thing to keep in mind is that, although the mathematics should certainly be treated, these articles should also give useful information to readers who cannot understand the math. Looie496 (talk) 21:59, 2 January 2009 (UTC)
thread_title: Reorganizing the field of MEMBRANE POTENTIALS

message: The article will be messy for a while until i finish editing. It may take several daysRvfrolov (talk) 22:41, 2 January 2009 (UTC)
thread_title: Reorganizing the field of MEMBRANE POTENTIALS-2

message: this is an important and underappreciated aspect of the membrane potential and is becoming much studied by those concerned with long term effects of cholesterol reduction strategies and the effect on muscular organs like the heart. Glynwiki (talk) 08:06, 14 August 2009 (UTC)
thread_title: Prevention of leakage of the H+ and Na+ Transmembrane Potential by Sterols

message: i dont think that the page talks about the amount of ions that are being moved by the channels, it makes a slight hint that neutrality would take a while to re establish however.  —Preceding unsigned comment added by Nibelhim (talk • contribs) 16:09, 16 February 2010 (UTC)
replies: text: Are you talking about ion channels or ion pumps? Looie496 (talk) 22:11, 16 February 2010 (UTC)
replies: text: Voltage gated channels24.203.202.14 (talk) 00:05, 17 February 2010 (UTC)
thread_title:  ion number 

message: The part about voltage is not correctly written. Voltage is due to a barrier and a difference in charge.one side of the barrier might be high or positiv in charge, the other side must be the opposite in charge. If the barrier is zero in resistance no voltage will occur, because the current might flow freely. So if one wants voltage differece, one needs to create a barrier for currents. One might create a large barrier for current , voltage will then be maximal (open contacts) currents will be zero. But when a current runs due to a lower barrier voltage will drop.
Anthony (talk) 13:44, 12 September 2010 (UTC)
thread_title: Moved from article

message: (The following material was inserted by  at the top of the article -- I am moving it here because it trashes the layout, and needs to be properly interwoven with the rest of the article. Looie496 (talk) 15:12, 18 August 2011 (UTC)
thread_title:  Notes from R.Bingelli 

message: If far more potassium leaves the cell than the amount of sodium that enters, why doesnt't  the cell get depleted of sodium?  — Preceding unsigned comment added by Ingelix (talk • contribs) 13:33, 3 September 2011 (UTC)
replies: text: I don't understand the question.  The cell is depleted of sodium, in the sense that the concentration of sodium ions inside a cell is always very low. Looie496 (talk) 16:27, 3 September 2011 (UTC)

text: Although the intracellular concentration of sodium is low, it isn't zero, ever, and there is enough internal sodium to meet whatever needs the cell has. --Tryptofish (talk) 19:32, 3 September 2011 (UTC)
thread_title: Lack of explanation?

message: I'm not an expert on any of the areas that I'm discussing but something is not right with the schematic because it doesn't reflect the Goldman equation. First off, K^+, NA^+, and CA^+2 are all positively charged, the battery terminals should reflect that. Short bars are positive and long bars are negative. The circuit for CA^+2 is suspect since the Goldman equation is for monovalent ions. Maybe.  — Preceding unsigned comment added by Pgrimes21 (talk • contribs) 11:15, 20 September 2011 (UTC)
replies: text: I believe the diagram is correct.  K ions are indeed positive, but they have a higher concentration inside the membrane than outside, the reverse of the situation for Na and Ca ions.  I don't think the fact that Ca ions are bivalent invalidates the diagram. Looie496 (talk) 14:52, 20 September 2011 (UTC)
replies: text: Speaking as an electrophysiologist but not an electrical engineer (so I'm pretty comfortable with the physiology, but less so with the conventions of drawing circuit diagrams), I also think the image is OK. Na+ is positively charged, and the direction that it moves across the membrane is from external to internal. K+ is also positively charged, but it moves in the opposite direction, and thus the opposite orientation of the symbol. Cl– moves in the same direction as Na+, but has a negative charge, so the symbol is oriented as for K+. Finally, Ca2+ moves in the same direction as does Na+, but as you say, it is divalent. If you take a look at the section of the page just following where the image appears, you will see that it says that the Goldman equation can also be expressed in a form that includes Ca2+, if desired. When this is done, the denominator becomes zF (as in the Nernst equation a bit higher up on the page), where z is the charge of the ion, in this case 2 for Ca2+ and 1 for everything else. (Actually, it's –1 for Cl–, but you'll notice that the ratio of logs is inverted there, which accomplishes the same thing.) --Tryptofish (talk) 19:33, 20 September 2011 (UTC)
thread_title:  Cell Membrane Equivalent circuit.svg 

message: Reading through the first part of this article, I'm having an issue with the definition of voltage. Voltage is a difference in energy between one place and another. It does not make sense to talk about the voltage at one location. In the first paragraph, the article talks about the membrane voltage being equal to (V interior - V exterior). But this doesn't make sense because there is no such thing as V interor and V exterior (it's also circular to define voltage in terms of voltage). You can't talk about a voltage at one place, because voltage is the *difference* between two places. The 'article' seems to understand this distinction because father down it says "but there is no instrument that can measure the voltage at a single point: the concept has no meaning". Yet throughout, the article talks about the different voltages at two points. The voltage *IS* the difference between the two points. There is no voltage at point A in a circuit and a different voltage at point B. There is a voltage between points A and B. In the case of membrane potential, there is no voltage on the outside and a different voltage on the inside, there is a voltage between the inside and the outside. Rather than define the membrane potential as Vm = (V interior - V exterior), why not instead use the equation Vm = (Zeuss - flying unicorns)? They are equally non-existent. (Sorry to be snide, I couldn't resist). Basically defining voltage this way would be like defining the distance that Bill is standing from Susan as 'the distance between Bill minus the distance between Susan'. It doesn't make sense.
There is also an attempt to define voltage in terms of it's ability to drive current. This is probably wise, but it ignores the role of resistance. It doesn't mention resistance. In fact, I can't find Ohm's law anywhere in the article which seems strange for an article on voltage, since Ohm's law IS basically the definition of voltage.
I think that the first part of the article should be re-written to give a more realistic definition of voltage, but it's hard to know what level to pitch it at. I understand that it is probably ill-advised to go back to the first-principles of thermodynamics and free energies to generate an accurate description, but we should be able to come up with something that is both accurate and understandable.
I would note that we had an extensive discussion on this topic several years ago in connection with this article, but it seems, since then, to have reverted to an incorrect definition of voltage.
-- On a smaller note, I deleted the line about the voltage-dependence of the NMDA channel that appeared under the 'voltage-dependent channels' heading.  It was completely incorrect.  The NMDA channel itself does not have appreciable voltage-dependence.  Its apparent voltage-dependence derives from the voltage-dependence of magnesium blockage of the open channel, not from a voltage-dependence of channel gating, as had been stated.  I thought about modifying the statement to reflect this, but then it became irrelevant to the topic of the heading, so I thought it best to just delete it.  Synaptidude (talk) 15:22, 23 October 2011 (UTC)
replies: text: Regarding Vinterior - Vexterior, you're correct of course, but every time I tried to remove that statement, somebody put it back, and eventually I just gave up and tried to edit around it rather than removing it. People have been taught that formula as the definition of membrane potential, and it's hard to unteach it. Regarding Ohm's law, the objective there was to say it in a way that would make sense to somebody who knows very little about electricity. If you see a better way to explain it, please take a shot. Regarding ion channels, I think this article needs to explain as clearly as possible what an ion channel is and the variety of things that can control them, but I agree that descriptions of specific types of channels are out of place here, except as examples. Looie496 (talk) 15:52, 23 October 2011 (UTC)

text: Please dive in, Synaptitude. Most of the article is unsupported by sources, and if you're confident, just go ahead and make changes there.  If you believe content that cites a reliable source needs changing, please cite a source that supports your change. The way to instill a degree of stability and permanence in your contributions is to cite (with page numbers) a reliable source (textbook, journal article, etc.) supporting them. Ask here for help constructing citations if you need it. In terms of accessibility, try to pitch it at a first year psychology student. Welcome back. --Anthonyhcole (talk) 16:21, 23 October 2011 (UTC)

text: As elsewhere, I think the trick to aim for is to make it accurate while also keeping it brief and simple. I agree that voltage is a difference, and I think what confuses lay people is that the voltage across the membrane is indeed the difference in voltage between outside and inside, but that doesn't mean that there's one voltage inside and another voltage outside and you just have to subtract one from the other. Actually, the "exterior voltage" is just ground. I also agree that resistance and GHK are important. --Tryptofish (talk) 18:03, 25 October 2011 (UTC)
replies: text: I replied but somehow it ended up in the wrong part of the talk - I'm sure you'll find it.  I'm also thinking that the first diagram needs to change.  There are not enough negative charges in it, and I think that might be confusing to someone trying to suss it out.  From the diagram, one might expect the inside of the membrane to be close to the outside in potential.  Also, it's not clear what the triangles are.  Ion channels? Gradients?  Conceptually it's OK, but I think the 'math' needs to add up better.  Also I think it could be better designed to show that the counter-ions are essentially across the membrane from each other (on the membrane capacitance).  I know, I know, just dive in, and I will.  Synaptidude (talk) 03:31, 26 October 2011 (UTC)
thread_title: An Issue 

message: I wrote an interactive tutorial "The origin of the resting membrane potential" which was intended as a teaching aid for my own students (UK university) but which is available for public view. I've had a number of nice e-mails from students (and some staff) in other universities who seemed to find it helpful, so I thought it might be appropriate as an external link on this page.
In line with Wikipedia guidelines I'm putting this on the talk page, and inviting another editor to insert this link into the article if they feel it appropriate. I suggest the tag "Interactive Tutorial".
http://www.st-andrews.ac.uk/~wjh/neurotut/mempot.html
Wjheitler (talk) 11:19, 30 January 2014 (UTC)
thread_title:  Interactive tutorial proposed external link 

message: Substituted at 23:41, 29 April 2016 (UTC)
thread_title: Assessment comment