Lecture 17 Bioelectricity II

Lecture 17 Bioelectricity II - Bioelectricity II Dr. Frame...

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Bioelectricity II Dr. Frame BME 100 November 2, 2011
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Overview Review Measuring bioelectricity
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Donnan equilibrium requires that space charge neutrality is maintained. The number of ions inside and outside determine charge. Na + K + Na + K + Cl - Cl- A - The number of positive charges and negative charges must be equal in a space.
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The Nernst equation: electrochemical potential determines which way ions move. Na + K + Na + K + Cl - Cl- A - Electrical Flux (drift) If more – ions inside, then – ions will exit and + ions will enter…if they can. Diffusion (chemical) If more K inside, then K will exit, if it can.
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K + K + Na+ Na+ Cl- Cl- A- E K = 26 ln[K o /K i ] or 60 log [K o /K i ] E Na = 26 ln[Na o /Na i ] or 60 log [Na o /Na i ] E Cl = 26 ln[Cl i /Cl o ] or 60 log [Cl i /Cl o ] Nernst Equations: predict ion movement
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Nernst Equations: predict ion movement K + K + Na+ Na+ Cl- Cl- A- Ion E x K -74 Based on Vm and on [K o ] vs. [K i ], potassium will be in equilibrium if the membrane potential is -74mV. Na +55 Based on Vm and on [Na o ] vs. [Na i ], sodium will be in equilibrium if the membrane potential is +55mV. Cl -60 Based on Vm and on [Cl i ] vs. [Cl o ], chloride IS ALREADY at equilibrium. Vm = -60mV Nernst describes the Vm where equilibrium for each ion will occur.
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Equilibrium: no net changes. Cell membrane Channel for ion I- I- I- I- I- I- I- -60mV inside 0mV out I- I- I- I- I- I- electrical chemical E I = -60mV
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Not Equilibrium: Net movement required. Cell membrane Channel for ion X+ X+ X+ X+ X+ X+ X+ -60mV inside 0mV out X+ X+ X+ X+ X+ X+ chemical electrical E x = -80mV
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Nernst Equations: predict ion movement K + K + Na+ Na+ Cl- Cl- A- Ion E x Vm In/Out K- 7
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Lecture 17 Bioelectricity II - Bioelectricity II Dr. Frame...

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