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How does electricity flow through the body?

  1. Apr 9, 2010 #1
    Hello everyone,

    Ok so electricty must flow through ions in the body right, I have some questions about this.
    From what I researched this is my understanding of it, please correct me if I'm wrong.

    When electricity passes to your body, the positive ions migrate towards the negative charged area and gains electrons while negative ions migrate towards positively charged area and releases them. Now I have some questions about that.

    1.Can't the positive ions gain electrons and completely neutralize the current?
    2. If the positive ions move towards the negative side and balance the charges at both ends, wouldn't that neutralize the current, why do redox reactions occur to keep a current going?
    3. Electricity is movement of electrons, here the ions are moving so can we really say the electricity is conducted in the ionic solution?
    4. I also like to know when a hair fryer is placed on water (obviously not for real), how does water conduct the electricity, using my logic where do the negative ions release electrons, I mean what is their to gain them?

    Thank you :smile:
     
    Last edited: Apr 9, 2010
  2. jcsd
  3. Apr 9, 2010 #2

    Andy Resnick

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    The currents are generally low because the resistance is high. For example, the current through renal epithelial tissue is around a micro-amp/cm^2. I don't know what the current is for an action potential, though.

    As for your last question, pure water is not conductive at all- it's around 13 MOhms/cm. Dissolved *salts* increase the conductivity, because those charges are very mobile in the presence of a voltage- lots of current is generated.
     
  4. Apr 10, 2010 #3
    Thanks for the response :smile: Since electricity if flow of electrons. Do we take movement of negative ions as electricty. Also when salt water gets electricity, do the ions eventually become deionized?
     
  5. Apr 10, 2010 #4

    Borek

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    18 MΩ/cm
     
  6. Apr 10, 2010 #5

    Borek

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    I would love to know what you mean...

    You have two reactions taking place, at two ends. In one electrons go into the body, at the other they are leaving. So you can't think about one end only.

    No, it is transfer of charge.

    Again, two reactions at two electrodes - one being something inside the hair drier, other something on the way to ground. In this case it is more complicated, as you are dealing with an active current, so reduction/oxidation are switched twice in each cycle.
     
  7. May 18, 2010 #6
    1) yes they can, but what about the place where positive charges are leaving from. if positive charge leave that space, then it will essenstially make that place more negative, in other words its just a different way of thinking the traveling current.

    2)
    everything that happens inside the body has a purpose it just don't happens to neutralize, if everything was neutralized then your change in free-energy is 0, which means everything has reached its equilibrium. if all the reactions in the body reach equilibrium point then no reactions would beable to occur and body or cell would not exist. so in other words, the thing you are saying in 2 does occur, but you dont see it because it goes as non-existence.

    for example, take cellular respiration. if all the glucose and purvate goes on equilibrium, then velocity of forward and backward reactions are the same, sooo...essentially no reaction, you wouldn't see any change. so, this is the reason for us to have enzymes. electronic nature can also reach equilibrium, but our enzyme chemically control it so it would not reach equilibrium. body use compounds to create current, which come from movement of charges.

    when i say movement of charges, negative charge does not necessarly travel. you could also say that positive charged particles moved toward some direction, leaving the initial place as negatively charge......and it keeps on going....soo you have a current!!


    3)
    of course!, what is electrochemical bettery my friend!. its simply oxidation-reduction reactions ------------which is?....transfer of electrons!

    4.
    water is not a good conductor of electricity. salt water is!. not good conductor doesn't mean it don't conduct electricity, there is always some amount of uncertainty in everything. nothing is 100% perfect!
     
  8. May 18, 2010 #7
    remember, the books of classical physics are still written in a way that positive charges are moving in electricity.

    this is early years of electromagnetics, physicist thought positiver charges were moving instead of neg. charges. it was later understood that there are 3 parts of atom: electrons, protons, and nutrons. later found that electrons are outside, which are freely moving around in electron clouds (quantum levels).

    so overall, just explaining that you could also think of electricity as moving of positive charges. just depends on you perspective of thinking.
     
  9. May 18, 2010 #8
    Well, the usual example of an action potential shows the voltage of the inner membrane moving from -70mV to ~40mV and back to -70mV in about 5ms, http://1.bp.blogspot.com/_4Oy_7FFvA...doutpsyde.com+300px-Action-potential.jpg.png".

    Using the formula i= C*(dv/dt):
    C= 2 µF/cm2 = 2x10-6
    dv= 40mV-(-70mV)=.110V
    dt= .005 sec

    So if my calculations are correct (I love saying that :tongue:) i = 2x10-6* (.110V/.005sec) = 4.4x10-5A/cm2. So about 44microamps per square centimeter. Multiply that by the area of the membrane to find the total current.

    If I made a mistake anywhere please don't hesitate to correct me.
     
    Last edited by a moderator: Apr 25, 2017
  10. May 18, 2010 #9

    Gokul43201

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    <cough>18 MOhm*cm</cough> :wink:
     
  11. May 18, 2010 #10
    good job my friend...
     
    Last edited by a moderator: Apr 25, 2017
  12. May 18, 2010 #11

    Moonbear

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    I don't have anything to add to this thread. I just had to stop in to comment that I LOVE reading threads like this. When I first joined this forum many moons ago, I used to feel I had to constantly explain to physics students that biology DOES involve physics. It's nice coming in now and seeing physicists and chemists responding to a biology (physiology) question with physics and equations! :biggrin:
     
  13. May 19, 2010 #12

    somasimple

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    Since K+ gradient makes the outer cell positive how is it posible to find :
    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1396124/?tool=pubmed
    By the way the notion of membrane capacitor is subject to discussion: It is possible to prove it doesn't work/exist.
     
  14. May 19, 2010 #13

    alxm

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    Since nobody pointed this out:
    A large enough voltage can and will ionize things. This is called the 'breakdown voltage' of an insulator. A big enough voltage will pass through anything, even vacuum.

    In this context, water is actually relatively easy to ionize. So while pure water is a pure conductor, it's still a very good one compared to most (if not all) oils, which are difficult to ionize. (In fact, when insulating oils become conductive in practice it's usually due to contamination with water or other things.)

    So you often have a situation where the more ions you have, the more current passes, generating even more ions, lower resistance and even more current (Known as http://en.wikipedia.org/wiki/Negative_resistance" [Broken]). This is what happens when electricity arcs through a gas for instance. This is why fluorescent lights take a second to light up: They have to build up sufficient voltage to make the initial arc. Or for instance, if you move a grounded object towards a charged wire so that it starts arcing, you have to move it farther away than the initial distance to stop the arcing.

    (Or if your transformer oil gets dirty, it could start arcing from the transformer to the surrounding casing, causing the oil to gasify and the arcing to increase further until the temperature and pressure build up and the thing explodes! Or would, if they didn't have safety valves to stop this from happening)
     
    Last edited by a moderator: May 4, 2017
  15. May 19, 2010 #14
    I screwed up. The http://1.bp.blogspot.com/_4Oy_7FFvA...doutpsyde.com+300px-Action-potential.jpg.png" shows the maximum voltage at roughly t=2.4msec and the initial voltage at roughly t=1.2msec, so that would make dt=.0012sec. So the average current per square centimeter during the rising phase would be closer to (5/1.2) the value I posted, so closer to 180 microamps per square centimeter. I'm surprised no one called me out on that.
     
    Last edited by a moderator: Apr 25, 2017
  16. May 20, 2010 #15

    somasimple

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    Biology says that ions are in equal quantity inside and oustide before the difusion process takes place, so :
    If P stands for positive and N for negative ions, a, b are integer o=outside and i= inside.
    the solutes are electroneutral =>
    a(Po+No)=0 and b(Pi+Ni)=0
    If a membrane is semipermable to one ion, P and if the concentration is greater inside then you find a potential that is something like that:
    V=k Log(Po/Pi).
    It is clearly a difference from two concentrations of the form : V= k2*(Po-Pi)

    How does biology removes the No and Ni terms?
    In fact, how biology is able to stop the electrostatic/electric forces that come from negative charges?
     
    Last edited: May 20, 2010
  17. May 20, 2010 #16

    Borek

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    N terms are not removed and they should be included. If they are not that's probably because in the cells they are not actively transported so their concentrations remain constant, and as such can be ignored to make calculations easier.

    Such simplified models are used very often and they prove to be useful. Problems arise when people start to think that these simplified models are the real ones. Unfortunately, that happens quite often when scientists from different branches speak about chemistry - they have no idea laws they are using are special cases, "dumbed down" to describe some part of the reality, but not applicable outside.

    My guess is that chemists are guilty as well, just in different areas.
     
  18. May 20, 2010 #17

    somasimple

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    Borek,
    I agree but how is it possible at a moment to say :
    The solution is electroneutral because all charges are taken in account.
    And a second after, we may forget one of the species.

    If you try to make a simple drawing showing the electrochemical diffusion process, you will face to an/several impossibility.
    The system will be divergent and self stopping: it doesn't work.

    A model may be described from its start (IC) to the end, without any hole.
     
  19. May 20, 2010 #18

    Borek

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    We do it all the time. It is called approximation.
     
  20. May 20, 2010 #19

    somasimple

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    A severe approximation may create a model that does not reflect the reality of facts.
     
  21. May 21, 2010 #20

    somasimple

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    How far an approximation is scientifically acceptable?
    5%? 10%? 50%? Less? More?
    If a solute contains k negative charges and k positive charges homogeneously distributed and all charges having the same valence,

    Is it fair to say :
    1/ The solute is neutral.
    2/ The solute is positive by approximation.

    Biology stands in the second allegation in the present case.
     
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