Lecture 3 Membrane Potentials

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Department
Biology/Animal Physiol & Neurosc
Course Code
BIPN 100
Professor
Laurie Smith

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10.4.13 Lecture 3  Channel proteins make a hole in the membrane that ions can cross through, making membranes permeable to ions  channels are specific, they allow only specific ionic species to cross, not allowing other ionic species to cross  Leak channels: creates resting potential  allows ions to leak across the membrane  selective for potassium  pathway: slow movement of potassium out of cell into the extracellular space  Eventually, the concentration of K inside and outside the cell would be the same because potassium would be added to the extracellular fluid  K outsideever equals Kinsideunless we die) because there’s another kind of protein in membrane that binds sodium and potassium and translocate the two ions, it pushes potassium into the cell and sodium out of the cell  It is moving the ions against concentration gradients and electrochemical gradients  Energy is added to the system via hydrolysis of ATP to move sodium against its electrochemical gradient, keeping concentration inside and outside the cell very stable  The resting membrane is not necessarily in equilibrium, it could be very close or very far  When the resting membrane potential is maintained away from equilibrium potential, it is accomplished by continuously adding ATP(energy) to the system  When an ionic current moves across the membrane, it brings resting membrane potential TOWARD but not necessarily TO E ion. (e = Δ I x R)  when K flows, it brings membrane potential toward potassium’s equilibrium potential   The permeability to potassium is much greater than that of sodium (100x greater) initially. It’s the resting state of most cells.  This is a common situation  Because sodium pushed outward and potassium inward  If permeability to sodium got bigger, the membrane potential would move towards sodium equilibrium potential  If they were equal, the membrane potential would be ~0  We would expect that in a multi-ionic current, ohms law would be true. But can’t use Nernst because we can only use it for ion at a time. Can’t find E for all of them at once!!  If you have a situation in which both potassium and sodium can move through a membrane (which is common) use…  Goldman-hodgkin katz eqution   If current small, it wouldn’t have that much of an effect as one with a bigger current  RT/F = 61  THERE IS NO z  Chloride is INSIDE on the top, OUTSIDE on the bottom  The only things in this equation can have only a + or – charge, cannot be +2 or -2  The membrane potential cannot be changing, or you can’t use this equation  How neurons encode and transmit signals  Via changes in the Vm based on changes in ionic currents through the membrane   Action potential: change in membrane potential  This particular neuron has a resting potential of about 60  With an electrical d
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