124CHAPTER 18 18.41(a) The area of each surface of this axon membrane is ()( )( )6620.10 m21010m210mArπππ−−==×=×A2and the capacitance is 6212220-8210m3.0 8.8510CN m1.010 mACdκ−×=∈=×⋅×81.6710F=×In the resting state, the charge on the outer surface of the membrane is ( )8391.6710F7010V1.1710C1.210iiQCV−=∆ =××=×→ ×9−C The number of potassium ions required to produce this charge is 99+-19K1.1710C7.310 K ions1.610CiQNe+−×= ××and the charge per unit area on this surface is 92-62-191.1710C1 10m0m1.610C1 ÅiQAσ×××0222421 1 8.610 Å290 Åee==×2eThis corresponds to a low charge density of one electronic charge per square of side 290 Å, compared to a normal atomic spacing of one atom per several Å . (b) In the resting state, the net charge on the inner surface of the membrane is
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