5-Elec Signals Neurons Figs BW

If cell is most permeable to potassium the resting

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Unformatted text preview: e resting potential will be closest to potassium. -how do you figure this out? through goldman-hodgkin-katz equation, calculate membrane potential of cell with permeability to all 3. -if 2 contribute equally, membrane potential will be in between them, half -membrane potential approach equilibrium potential of whatever contribue most EK Goldman-Hodgkin-Katz Equation: Vm=61 log PK [K+]out + PNa [Na+]out + PCl [Cl-]in mV PK [K+]in + PNa [Na+]in + PCl [Cl-]out Something to Remember ***IMPORTANT (VERY VERY VERY)***: -so sodium increase, Vm approach that. If the permeability for a particular ion increases, the membrane potential will change, tending to move toward the equilibrium potential for that ion. Ion Leakage and Na+/K+ Pumps K+ 5 mM OUT Na/K pump 145 mM 150 mM 15 mM IN Na+ ENa = +60 mV 2 K+ EK = -90 mV ATP inner ear is exception: sodium and chlroide always inward except in inner ear. tricky: potassium may not be always outward. but there's a problem in that channels are leaking all the time. arc=nerve cell at rest, above is extracellular fluid. membrane is more permeable to potassium in that more potassium channels are open than sodium channel at rest. membrane potential is going to be in between the equilibrium potential of sodium and potassium (~ -70mV). here's the problem: the equlibrium potential for potassium at -90 means that outwardly directed concentration -driven flux of potassium is equal inwardly directed electrically-driven flux only at -90. at other potential, -70, this is not true. the membrane is 20 mV out of equilibrium, so outward concentration-driven flux do not equal and oppositive of inward electrical driven flux. in fact, the outwardly concentration flux is greater than inward electrical-driven flux. so there's a net outward movement for potassium. under these condition means theres a constant leak of potassium out of cell, which is bad b/c sodium-potassium pump burn a lot of ATP to stuff cell with potassium which are leaking out. what's worse is that some sodium channels, although not as ma...
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