L16 - Wednesday,November3,2010 Reading...

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Wednesday, November 3, 2010 Ion Transport and Excitable Membranes Reading: Chapter 12, pages 387-414  Objectives Role of charge in the distribution of ions across membranes.  o Plasma membranes of animal cells are permeable to K + , but not Na + . o Why doesn't K +  equilibrate across the membrane? Because K +  ions are  charged, and charge separation is unfavorable. o A lipid bilayer is an insulator, and therefore can act as a capacitor. Gedanken (thought) experiment: open K +  channels in the plasma membrane, and  see what happens.  o As K +  flow out, the inner surface of the membrane becomes negative and  the outer surface becomes positive; i.e., an  electrochemical potential  forms across the membrane. o The magnitude of this potential is described by the  Nernst equation . o The equilibrium potential for K +  is about -85 mV, similar to the actual  potential across plasma membranes. A more accurate measure of  membrane potential is provided by taking into account the  permeability  of  the plasma membrane to different ions. Initiation of the action potential in nerve cells. 
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This note was uploaded on 02/09/2011 for the course BIOS 20182 taught by Professor Lahn during the Spring '11 term at UChicago.

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L16 - Wednesday,November3,2010 Reading...

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