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    I understand how a resting potential is established, but I don't get how it's maintained if you're still pumping 3 sodium ions out and 2 potassium ions in. Can anyone explain this? (exam board is OCR)
    thanks
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    (Original post by Cryinglightning)
    I understand how a resting potential is established, but I don't get how it's maintained if you're still pumping 3 sodium ions out and 2 potassium ions in. Can anyone explain this? (exam board is OCR)
    thanks
    Hey.
    F214?
    I'm sure I can hand a little help here, as I study the same specification as you.

    Right, so?
    The basics is that the resting potential is the maintenance of a potential different across the neuronal membrane via the 3:2 ratio pumping of sodium and potassium ions out and in the cell respectively.
    The mechanism states that they're (ions) are transported via active transport.
    Furthermore, I'm sure the maintenance is sustained through the fact that sodium ions causes LOWER permeability within the cell thus sustaining your sodium-ion electrochemical gradient.

    Likewise, potassium ions cause HIGHER permeability via diffusion out of the cell, moving down the potassium ion concentration gradient.

    Simultaneously speaking, this will maintenance the testing potential to the approximate value range of -60-70mV.

    Does that make any sense?

    I hope this helped at least a little!

    (This was four-mark question in January 2013, if I remember correctly?)
    You can check against that mark scheme too if to wish.

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    (Original post by Cryinglightning)
    I understand how a resting potential is established, but I don't get how it's maintained if you're still pumping 3 sodium ions out and 2 potassium ions in. Can anyone explain this? (exam board is OCR)
    thanks
    3 positive ions are leaving, but only 2 are entering. That means there's a net loss of 1 positive ion which means that the difference in charge between the inside and outside of the membrane will be negative in the resting state.
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    (Original post by Ché.)
    Hey.
    F214?
    I'm sure I can hand a little help here, as I study the same specification as you.

    Right, so?
    The basics is that the resting potential is the maintenance of a potential different across the neuronal membrane via the 3:2 ratio pumping of sodium and potassium ions out and in the cell respectively.
    The mechanism states that they're (ions) are transported via active transport.
    Furthermore, I'm sure the maintenance is sustained through the fact that sodium ions causes LOWER permeability within the cell thus sustaining your sodium-ion electrochemical gradient.

    Likewise, potassium ions cause HIGHER permeability via diffusion out of the cell, moving down the potassium ion concentration gradient.

    Simultaneously speaking, this will maintenance the testing potential to the approximate value range of -60-70mV.

    Does that make any sense?

    I hope this helped at least a little!

    (This was four-mark question in January 2013, if I remember correctly?)
    You can check against that mark scheme too if to wish.

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    yeah its F214 :P and that makes sense, thanks!
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    (Original post by Democracy)
    3 positive ions are leaving, but only 2 are entering. That means there's a net loss of 1 positive ion which means that the difference in charge between the inside and outside of the membrane will be negative in the resting state.
    Yeah I get that bit, but then surely if that continues it just keeps getting more negative rather than staying in a range? I think its like Ché said and the membrane is more permeable to potassium ions so overall there is no net gain once the resting potential is reached
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    Hated it back in the day when I was doing it
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    (Original post by Cryinglightning)
    yeah its F214 :P and that makes sense, thanks!
    No, thank you!
    I wasn't exceptionally sure but you've confirmed I'm competently confident on that topic!

    How are you liking F214?
    It's the freaking best for me at the moment!


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    (Original post by Cryinglightning)
    Yeah I get that bit, but then surely if that continues it just keeps getting more negative rather than staying in a range? I think its like Ché said and the membrane is more permeable to potassium ions so overall there is no net gain once the resting potential is reached
    Due to the sodium-potassium pump, [K+] is high inside the cell and low outside the cell whereas [Na+] is high outside and low inside the cell. As you say, the net movements in charge mean that the cell becomes negative.

    There are additional K+ ion channels on the cell membrane so there is an outward diffusion of K+ ions down its concentration gradient. This leaves a greater yet negative charge inside the cell.

    However, there comes a point where K+ is attracted back into the cell by this negative charge (an electrostatic attraction).

    When outward K+ flow along its concentration gradient equals inward K+ flow along its electrochemical gradient, an equilibrium is established. The membrane potential at this equilibrium is the equilibrium potential for K+.

    A similar principle applies for all the other ions (mainly sodium, chloride and calcium) and they will all have their own equilibrium potentials. Na+ for example, will move into the cell down its concentration gradient making the cell more positive until it forms an equilibrium with Na+ ions being repelled out of the cell due to electrostatic forces.

    The equilibrium potential for K+ ions is around -90 mV and around +50 mV for Na+. If the membrane was equally permeable to sodium and potassium, then you would expect the resting potential to be in the middle (ie -20 mV), but in fact there are many more open potassium channels at rest than sodium channels so the resting potential lies towards that of potassium.

    The overall resting potential varies depending on the type of cell but is usually around -70 mV for a neuron and is more negative in muscle cells.
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    (Original post by Asklepios)
    Due to sodium-potassium pump, [K+] is high inside cell and low outside cell and [Na+] is high outside and low inside the cell. As you say, the net movements in charge mean that the cell becomes negative.


    There are additional K+ ion channels on the cell membrane so there is an outward diffusion of K+ ions down it's concentration gradient. This leaves a greater yet negative charge inside the cell.

    However, there comes a point where K+ is attracted back into the cell by this negative charge (an electrostatic attraction).

    When outward K+ flow along its concentration gradient equals inward K+ flow along its electrochemical gradient, an equilibrium is established. The membrane potential at this equilibrium is the equilibrium potential for K+.

    A similar principle applies for all the other ions (mainly sodium, chloride and calcium) and they will all have their own equilibrium potentials. Na+ for example, will move into the cell down it's concentration gradient making the cell more positive until it forms an equilibrium with Na+ ions being repelled out of the cell due to electrostatic forces.

    The equilibrium potential for K+ ions is around -90 mV and it is around +50 mV for Na+ ions. If the membrane was equally permeable to sodium and potassium, then you would expect the resting potential to be in the middle (ie -20 mV), but in fact there are many more open potassium channels at rest than sodium channels so the resting potential lies towards the equilibrium of potassium.

    The overall resting potential varies depending on the type of cell but is usually around -70 mV for a neuron but is more negative in muscle cells.
    Nice detail!
    Very nice...
    I'll use this for in-depth revision!



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    (Original post by Ché.)
    No, thank you!
    I wasn't exceptionally sure but you've confirmed I'm competently confident on that topic!

    How are you liking F214?
    It's the freaking best for me at the moment!

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    Yeah it's pretty good, still finding the nerve stuff a bit weird with potentials and stuff, too physicsy!! Photosynthesis is pretty cool though, just shows how much of GCSE biology was lies :P

    (Original post by Asklepios)
    Due to the sodium-potassium pump, [K+] is high inside the cell and low outside the cell whereas [Na+] is high outside and low inside the cell. As you say, the net movements in charge mean that the cell becomes negative.

    There are additional K+ ion channels on the cell membrane so there is an outward diffusion of K+ ions down its concentration gradient. This leaves a greater yet negative charge inside the cell.

    However, there comes a point where K+ is attracted back into the cell by this negative charge (an electrostatic attraction).

    When outward K+ flow along its concentration gradient equals inward K+ flow along its electrochemical gradient, an equilibrium is established. The membrane potential at this equilibrium is the equilibrium potential for K+.

    A similar principle applies for all the other ions (mainly sodium, chloride and calcium) and they will all have their own equilibrium potentials. Na+ for example, will move into the cell down its concentration gradient making the cell more positive until it forms an equilibrium with Na+ ions being repelled out of the cell due to electrostatic forces.

    The equilibrium potential for K+ ions is around -90 mV and around +50 mV for Na+. If the membrane was equally permeable to sodium and potassium, then you would expect the resting potential to be in the middle (ie -20 mV), but in fact there are many more open potassium channels at rest than sodium channels so the resting potential lies towards that of potassium.

    The overall resting potential varies depending on the type of cell but is usually around -70 mV for a neuron and is more negative in muscle cells.
    Thanks thats a great explanation
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    (Original post by Cryinglightning)
    Yeah it's pretty good, still finding the nerve stuff a bit weird with potentials and stuff, too physicsy!! Photosynthesis is pretty cool though, just shows how much of GCSE biology was lies :P



    Thanks thats a great explanation
    That's completely true!
    As long as you've got a decent knowledge of the main stages you'll be fine - the basic principles of an action potential, synaptic transmission, first and second messengers and the link with hormones such as beta cells and insulin secretion...
    The Hodder Education revision guide really breaks down content well - that's what I use...


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