Lecture 3 The Membrane at “Rest”

54 1z log ionoutsideioninside e ion is the membrane

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61.54 * 1/z * log [ion]outside/[ion]inside E ion is the membrane potential at which the net flow of the ion is 0 . this is for a specific type of ion i.e. Na+ and K+ have different E ion K+ found in large concentrations in cytosol (20:1 ration). When channels open up, K+ will flow to extracellular fluid and inside of cell will become more negative until it reaches equilibrium potential (will be somewhat negative) Na+ is opposite, more outside than inside (10:1). Flows inside of cell, and equilibrium potential will be positive Cl- like Na+ but brings (-) charge inside cell resulting in negative equilibrium potential (11.5:1) Ca^2+ stronger equilibrium potential than sodium (doubles electrical strength of each ion) A- is largely protein based; important for osmotic balance each ion has a specific concentration w/in cellular systems, and concentrations are highly maintained and regulated by specific proteins. We don't find large changes and so each of them have a specific ionic equilibrium potential that is maintained as a constant for cellular systems. No two of these ions will be at equilibrium at the same time
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Practice questions (see professor) such as What happens with changes in concentration? Increase extracellular K+... increase extracellular Na+... increase extracellular Cl-... Nerst equation only tells about equilibrium for 1 ion notice no ions will be at equilibrium at same time but what determines the membrane potential (V n )...? Multiple Ions, relative permeability, and the membrane potentials Relative permeability the ability of an ion to cross the membrane can be expressed relative to the ability of all other ions an ion that can cross more readily is said to have high “ relative permeability to an ion that passes less readily flow of ion(s) with high relative permeability contribute more to the membrane potential; ie membrane potential will be close to the ion's equilibrium potential. Relative permeability serves to weight the contribution of an individual ion to the membrane potential (which is mathematically incorporated into the goldman equation as P ion Vm = (61.54)log
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  • Fall '08
  • Kippin,T
  • Electric charge, Selective Membrane

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