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Homework Help: Action Potential with Nerve Cell and Finding Power

  1. Sep 7, 2012 #1
    1. The problem statement, all variables and given/known data

    During an action potential, Na + ions move into the cell at a rate of about 3 x 10^-7 mol / m^2 s. How much power must be produced by the "active Na+ pumping" system to produce this flow against a + 30 mv potential difference? Assume that the axon is 40cm long and 30 mu m in diameter.
    2. Relevant equations

    P = IV
    maybe R = ρL / A

    3. The attempt at a solution

    I understand I need to use P=IV but I don't understand how to incorporate the measurements of the axon without knowing the resistivity of the liquid. Should I assume water?

    P = (3.7 * 10^-7 mol/m^2 s)(0.03 V)
    P ≈ 9.09 * 10^-9 W
  2. jcsd
  3. Sep 7, 2012 #2


    User Avatar

    Staff: Mentor

    The diffusion rate is given in terms of moles per unit area per second. Use the axon dimensions to estimate area. You'll also have to convert the moles of charges into actual charge units (what's the unit charge of an Na+ ion in coulombs?).
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