BIOS 20175 Lecture Notes - Lecture 15: Cytosol, Patch Clamp, Membrane Potential
25 Jul 2020
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Document Summary
Because k+ ions are charged, and charge separation is unfavorable: a lipid bilayer is an insulator, and therefore can act as a capacitor. A more accurate measure of membrane potential is provided by taking into account the permeability of the plasma membrane to different ions. In this case the membrane potential switches polarity and becomes positive inside. Repolarization of nerve cells: soon after they open, sodium channels close again due to inactivation. K+ efflux then begins to repolarize the cell: eventually the system returns to its initial (resting) state, this entire action potential lasts only a few milliseconds. During a single action potential, only a tiny fraction of the na+ and k+ ions cross the membrane, so the gradients remain intact. Molecular description of channel behavior: individual channels can be studied by patch clamping. It turns out that a given channel switches back and forth between an open and a closed state.
