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LECTURE NOTES - PSY290 - Sept 24/2013 - Yeomans

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University of Toronto St. George
John Yeomans

- pumps separate ions - K: causes resting potential - how actionpotential initiates depolarization + - Na ions --> action potential spike, followed by closing of channels, triggered by K - -- release of... - postsynaptic potential --> computation, by transmitter action, activated by the 4 chmical transmitters - plasticity = result of transmitter release, or more/less PSP RESTING POTENTIAL - all healthy cells - -40 to -90mV - Na-K pump: ions pumped in opposite directions - 2K in, 1Na out (?) PUMPS - all cells have pumps and channels  - not all have gated channels  All potentials = result of moving ions across membrane K channels: - only ions that move freely - movement by diffusion (concentration gradient) - loss of + charged K --> soma more negative - when free flowing, equilibrium potential When Na is only ion that flows, potential goes up to +50mV --> internal soma more positive When K free to flow, potential goes down to -90mV --> internal more negative Hotchkin & Huskley --> actually came up with formula to explain K and Na ion flow for resting & action potential Resting condition --> K flows best, therefore K controls resting potential --> doesn’t - quite reach -90mV due to flow of Cl , keeping resting potential at -70mV - there are K leak channels --> (which produce) easier flow + When action potential initiated --> opening of Na channels (when in depolarization) --> Na enters for a millisecond --> potential becomes +50mV (determined by strength of Na concentration gradient) + + 10x more Na outside; 10x more K inside Δ concentration→ Δ potential → voltage proportional to concentration difference (logarithmic relationship b/w voltage & concentration, explaining all concentration gradient forces) During AP (action potential) : all ion channels opened (refractory period) CONDUCTION - AP (action potential) conducts at max 130m/s SYNAPSE - each uses hundreds of proteins - what’s causing the release? Big depolarization --> spike opens special type of channel (voltage gated Ca channel) Calcium: - Ca is powerful ion -- muscle twitches, vesicle release, inside neurons (learning + memory) - So powerful that it is kept out of cell by Ca ion channels - presynaptic -- induces transmitter release at terminals - necessary step for induction of transmitter release - Ca causes vesicles to combine w/ presynaptic membranes, join membrane and releases contents --> causes exocytosis (transmitter release) Transmitters -- cause opening/closing channels, DNA transcription, postsynaptic signalling - once released, must b
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