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Medical Sodium Channels in refractory period

  1. Oct 19, 2005 #1
    After an action potential has passed the localised region enters its refractory period, and during the absolute refractory period a second impulse cannot be conducted regardless of the size of the stimulation. This is because the sodium channels cannot open immediately after closing, why is that?
     
  2. jcsd
  3. Oct 19, 2005 #2
    I asked this before:
    You mentioned the resting state must be re-established before another wave of depolarisation can occur, but there are sufficient ions in cells present for the nerve to be depolarised many times before the supply of ions runs out. Therefore, there is no reason why sodium channels should not be able to open due to that reason.
     
  4. Oct 19, 2005 #3
    I *think* it's because the gradient has been disrupted by the last impulse. No?
     
  5. Oct 19, 2005 #4
    Consider the ion concentration outside the cell as well?
     
  6. Oct 19, 2005 #5

    somasimple

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    Not really, there is few ions that are mobile. They are the fuel and ions channels are a kind of engines that work with ions.

    I made an animation of a travelling action potential (without ions channels)
    The refractory period exists when all ions are inside (there is another one when all ions are outside or crossing the membrane). Concentration is not playing a role since attraction and repulsion limit incoming/outgoing ions.
    http://www.somasimple.com/flash_anims/atomic14.swf
     
  7. Oct 19, 2005 #6

    somasimple

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    ps: red positive ions = sodium ad blue ones = potassium :redface:
     
  8. Oct 20, 2005 #7

    DocToxyn

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    You are correct that in the cell as a whole there are enough ions, but these events happen in very localized environments surrounding those channels. As pattylou points out, the ion gradient in that specific area has been disrupted, both inside and outside, therefore you need time and energy to allow structures like Na/K transporters to re-establish the proper distribution of ions.
     
  9. Oct 20, 2005 #8
    So am I correct in saying that the absolute refractory period is due to the lack of ions in the localised environments not because of the inability of the protein channels to open immediately after they are closed?
     
  10. Oct 20, 2005 #9

    somasimple

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    You're correct and the traditional electrical theory forgets the atomic forces that stop the incoming/outgoing flows. You may have a high Na concentration outside but ions can't get inside if there is already the maximum allowed by attraction/repulsion interactions.

    It is why there is a plateau when you change the gradient outside (increasing).
     
    Last edited: Oct 20, 2005
  11. Oct 20, 2005 #10

    somasimple

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