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    Hi all,

    Just wondered whether I could get some opinions on my description of the Resting Membrane Potential for some physiology notes I am writing:

    1) The Na+K+ATPase actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell. This establishes concentration gradients for Sodium and Potassium across the cell membrane.

    2) The plasma membrane is more permeable to K+ ions than Na+ ions. There are many more Potassium 'leak' channels in the open conformation whilst the sodium channels remain in the closed formation (a very small fraction remain open).

    3) Potassium ions diffuse out of the cell along their concentration gradient. The inside of the cell becomes increasingly negative due to this.

    4) This negative charge creates an electrical driving force which attracts some of the Potassium ions back into the cell via the leak channels.

    5) Eventually, the movement of K+ in and out of the cell will be equal (Net flux = 0) with the inside of the cell being more electronegative with the respect to the extracellular environment. The resting potential is established.

    Foot notes:

    1 - The RMP is not equal to the K+ equilibrium potential since there are other ion fluxes which contribute to the membrane potential and some of the potassium channels remain closed.

    2 - Na+K+ATPase indirectly contributes to the membrane potential since it is an electrogenic transporter.




    Any opinions much appreciated.

    Luke
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    Looks good If this is only for A level then A levels have included more detail since I did them! If it's not for A levels and you want more detail I can give some pointers.
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    (Original post by Calumcalum)
    Looks good If this is only for A level then A levels have included more detail since I did them! If it's not for A levels and you want more detail I can give some pointers.
    Thanks. This is actually for a physiology module as part of my medical degree. I don't have to write essays on this module, but have to do some short answer questions and MCQs so I suppose this is checking that I've understood the principles enough to pass!
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    (Original post by labt)
    Thanks. This is actually for a physiology module as part of my medical degree. I don't have to write essays on this module, but have to do some short answer questions and MCQs so I suppose this is checking that I've understood the principles enough to pass!
    Ah, my bad! Your sig confused me
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    you dont need to know that much, you show off
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    (Original post by labt)
    ...
    Your understanding is good. I'm not sure i've seen a description of membrane potentials without mentioning the Nernst equation before, but that may be a difference in teaching tbh. You mention other ions - maybe which would be useful? Do you have to know approximate intra and extracellular ion concentrations?

    (Original post by slacker07906)
    you dont need to know that much, you show off
    You go to Bristol med school, i take it :lolwut:
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    (Original post by nexttime)
    Your understanding is good. I'm not sure i've seen a description of membrane potentials without mentioning the Nernst equation before, but that may be a difference in teaching tbh. You mention other ions - maybe which would be useful? Do you have to know approximate intra and extracellular ion concentrations?



    You go to Bristol med school, i take it :lolwut:
    The Nernst equation has been taught to us in Lectures. More relevant to this scenario is the Goldmann Equation which takes into account the permeability of the membrane to other ions (notably the minor contributions of Na+ and Cl- in the resting state). The Nernst equation makes the assumption that membrane is freely permeable to only that ion.

    In essence, I think it would be useful to mention the fact that Potassium ion-gated channels are the main contributors to the resting membrane potential and that the Nernst Equation provides us with a hypothetical value of -90mV for its equilibrium potential. The resting membrane potential is not equal to this value due to the influence of Cl- efflux /Na+ influx which is why the Goldmann equation is probably more useful in this description.
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    :borat:
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    Seems pretty good.

    I suppose, as mentioned above, just remember about the Nernst equation for potassium, but then due to the Goldman-Hodgkin-Katz equation, the resting potential will be some mV more positive than just the Potassium Equilibrium Potential due to a small amount of sodium moving in.

    But yeah, just after I wrote that there, I see you've mentioned it above. lol
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    I'd mention what resting membrane potential value (about -70mV I think) you'd expect for your average neuron, and also how much ATP is used up per 3Na+/K+ (1, I think).

    If you can't remember whether Na and K go in or out, I remember for an ACTION POTENTIAL it's sodi-IN and pOUTassium, so resting potential is the other way round.
 
 
 
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