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5-Elec Signals Neurons Figs BW

they come from unequal distribution of ions and

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Unformatted text preview: from unequal distribution of ions and selective ion permeability. the slide show what happens when there's unequal distribution of potassium ion across membrane, higher outside than inside and when member is only permeable to potassium (have potassium channel): at this instant develop equilibrium condition where the diffusion of potassium through its channels in the outward direction (to the left) down the concentration gradient. this leave inside of cell negative because chloride can't follow. this outward movement of potassium will be match by inward movement of potassium down an electrical gradient (internal electronegativity) and cell out and in come to equilibrium rapidly. the inside of cell is negative with respect to outside. -thermodynamics come 2 ways to explain the fluxes: concentration and electrical movement. to calculate the potential difference is across the membrane, you have to set the 2 term equal to each other, put a minus sign on one of them. then you solve for potential across membrane, and come up with the nerst equation for potassium. at a given set of condition in human body (potassium equilibrium potential Ek) depend on ratio of ion concentration what we know: if membrane is only permeable to potassium, the membrane potential will be negative. on the right hand side, if membrane is only permeable to sodium, the membrane potential will have positive value (positive inside with respect to outside). the permeability is due to selective ion channels that have gates which are open to certain molecule. we know that gates are controlled by binding of ligands, voltage. Vm When One Ion is Permeable only K+ is permeable ICF ECF low K+ Cl- Na+ only Na+ is permeable ICF ECF high K+ Cl- low K+ Cl- high K+ Cl- Na+ high K+ low Na+ ClNa+ Clconcentration + K electrical K+ high K+ low Na+ ClNa+ Clconcentration Na+ electrical + Na +- -+ EK = 61 log [K]o [K]i mV Nernst Equation for K+ ENa = 61 log [Na]o [Na]i mV Nernst Equation for Na+ what if only sodium is permeable? -low sodium inside, high outside d...
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