Lectures3+4-Chapter_2-BiologicalFoundations

Cell membrane is not permeable to ions but ion

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Unformatted text preview: s the membrane. Cell membrane is not permeable to ions, but ion channels allow passage of Na+ and K+. Membrane potential would quickly break down if separation of charges is not restored. Sodium-potassium pump reverses ion flow by ejecting Na+ and returning K+ into cell. This allows the resting potential to be maintained. Generating the Action Potential Used For Neuronal Communication - 1 Alan Hodgkin (1914-1998) Using giant axons from squids Alan Hodgkin and Andrew Huxley published a short paper in the journal Nature in 1939 announcing their achievement of recording action potentials from inside a nerve fibre. In 1952 they published the first computational model on the generation of the action potential, predicting the existence of voltagegated Na+ and K+ channels. It is still the basis of most of the biophysical models of the action potential used in neuroscience today. Andrew Huxley (1917-2012) 46 Generating the Action Potential Used For Neuronal Communication - 2 Depolarization occurs when the membrane potential becomes more positive: More Na+ ions enter cell because the voltage-gated channel goes from “closed” to “open” There are also a set of voltage-gated K+ channels (open at a less negative membrane potential than the Na+ ones), causing K+ to rapidly leave the cell to re-establish the charge balance, “repolarizing” the cell. When enough K+ leaves the cell, the membrane potential will become negative enough so that both the voltage-gated Na+ channel and the voltage-gated K+ channels “reclose” Hyperpolarization occurs if enough K+ has left the cell so that the membrane potential becomes more negative than the ordinary resting potential - will repolarize by diffusion 47 Generating the Action Potential Used For Neuronal Communication - 3 48 Na+ influx into cell increases membrane potential (depolarization). If depolarization reaches threshold level for opening voltage-gated Na+ channels, the opening of these channels will cause a sudden “spike” in membrane potential. As the voltage inside the cell goes above the threshold level for voltage-gated K+ channels to open, these ions to leave the cell and...
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