BIO203_Neurophysiol_1

BIO203_Neurophysiol_1 - The Membrane Potential Ionic...

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The Membrane Potential Key background concepts: • ionic asymmetries of cations and anions, and electrically-charged molecules (proteins and macromolecular “fixed” charges, for example) across biological membranes • macroscopic electroneutrality • selective permeabilities (conductances) to charged species • ions are the charge carriers in (biological) solutions, and electrons are the charge carriers in solid conductors such as metallic wires Ionic Asymmetries of Cations and Anions Cl 150 35 low (generally) Two questions: 1. How are the ion concentration gradients established? 2. Why do these gradients not dissipate, or do they? Sherwood, Klandorf & Yancey, Animal Physiology: From Genes to Organisms , Table 3-4 Electrochemical Gradient The diffusive flux of a charged solute (an ion) is driven by: • concentration (chemical) gradient, and • electrical gradient What happens when both of these gradients are oriented in the same direction (either inward or outward)? Can you easily predict the direction of passive diffusion across a membrane? What happens when the two gradients are oriented in opposite
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BIO203_Neurophysiol_1 - The Membrane Potential Ionic...

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