PS111A Lecture 2 color

PS111A Lecture 2 color - PHYSIOLOGICAL SCIENCE 111A...

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PHYSIOLOGICAL SCIENCE 111A Professor Peter Narins Winter 2010 Lecture 2- Excitable Cells
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Figure 44.5 Ion Pumps and Channels Extracellular Fluid Intracellular Fluid Hi [Na + ] Low [K + ] Hi [K + ] Low [Na + ] Na + -K + pump maintains ionic gradient Cell membrane is selectively permeable to K + at rest (open) Many Few
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Neurons: Generating and Conducting Nerve Impulses Potassium channels are the most common open channels in the plasma membranes of resting neurons, and resting neurons are more permeable to K + than any other ion. • The sodium–potassium pump keeps K + concentration high inside the cell, but K + can diffuse out the open channels. • The membrane potential at which the tendency of K + ions to diffuse out of the cell down its concentration gradient (chemical force) is equal to their tendency to diffuse into the cell (electrical force- opposite charges attract) is called the potassium equilibrium potential .
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at equilibrium, F e =F c : zFV = RT ln [K + ] o [K + ] i V = RT ln [K + ] o = E K Nernst Equation considering K + zF [K + ] i log 10 x = 0.4343 ln x {Substitute log for ln, using this, also substitute values for [K + ] for real cell} E K = 0.058 log 10 [K + ] o [K + ] i E K = -90 mV This is the potential of a cell only permeable to K + (For Na + alone, E Na = +63 mV) Nernst Equation Derivation, Revisited Know these two numbers!!
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Goldman Equation Goldman Equation (Constant-Field equation): V m = RT ln P K [K + ] o + P Na [Na + ] o + P Cl [Cl - ] i F P K [K + ] i + P Na [Na + ] i + P Cl [Cl - ] o Takes into account the permeability of the membrane to more than one monovalent ion For only one permeable ion, it reduces to the Nernst equation Refer to upcoming slide for the derivation of the membrane potential considering only two ions: Na + and K +
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This note was uploaded on 02/03/2010 for the course NEUROSCI 101A taught by Professor Scheibell during the Winter '10 term at UCLA.

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PS111A Lecture 2 color - PHYSIOLOGICAL SCIENCE 111A...

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