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1d Action potential.doc

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BIOL 273
Norman Scott

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1d) The action potential Different from graded potential: i. amplitude in a single neuron not graded, always the same size (size doesn't depend on the triggering event) , change in membrane potential of 100mV (-70mV to +30mV) ii. Action potentials' amplitude does not decrease as they travel across neuron's membrane = suitable for long-d signal transmission - also has same duration iii. graded potentials arise from ligand-gated channels in the membrane while action potentials arise from voltage-gated channels (opens when receives pulse of electricity) - Na+ and K+ - open in response of depolarization (depolarization of a certain size = -70 must be brought to -55mV i.e. -15mV in size) of membrane (won't open in sub-threshold = smaller than = -15mV) - Na+ channels open instantly - K+ channels open after a delay of about half a millisec - Na+ channel has two gates (illustrated in notebook) - transmission of signal down the length of an axon - when Na+ ions flood into cell (opening of the Na+ channels), cell depolarizes, adjacent voltage-gates channels pop open at the same time (slightly afterwards) = positive feedback (inflow of Na+ > voltage > Na+ channels opens > inflow of Na+ > more Na+ channels open > wave of depolarization sweeps down entire length of axon - amplitude and duration is the same because it depends on two constant factors: a) the RMP b) length of time that the Na+ channels are open * Refractory periods: make the neuronal membrane much less resp
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