Excitatory or inhibitory ability to depolarize

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Unformatted text preview: rigger Local potential- short-ranged change in voltage (‘localized’) 4 differences btw local & AP’s: • LP’s are graded: magnitude is determined by strength/duration magnitude of stimulus of • More intense or prolonged stim’s open more Na-gates, & so, larger More voltage changes occur voltage • LP’s are decremental: weaken as they spread away from pt of weaken stimulus (K+ flow out, following Na+ entering) stimulus • LP’s are reversible: when stimulation stops, K+ diffusing out quickly returns RMP quickly • LP’s can be excitatory or inhibitory: ability to depolarize & ability hyperpolarize (more -) depending on neurotransmitter hyperpolarize Action Potentials Action Action potential- dramatic change produced by voltageregulated ion gates in p.membrane (an up & down shift in regulated membrane voltage) membrane • Occurs only when enough gates open (thus, high density of Occurs gates @ trigger zone) • ‘All-or-none’ principle of AP’s • If LP spreads to trigger zone & is still strong enough to open gates, then an AP is generated then Action Potentials Action 7 ‘phases’ of an AP• • • LP reaches axon hillock; Na+ arrive & depolarize membrane LP reaches depolarize LP inc to a critical voltage level (threshold, -55 mV) Neuron ‘fires’ (produces a AP) @ threshold causing voltage Neuron regulated Na-gates to OPEN quickly & K-gates open slower regulated • Positive feedback (Na causes more Na-gates to open) • Na-gates inactivated as voltage ~0 & begin closing; voltage Na-gates ~+35 mV when all Na-gates close ~+35 • @ peak, all K-gates are open & flow OUT to begin repolarizing peak, repolarizing membrane membrane • ISF becomes more – then before RMP (= hyperpolarization) ISF hyperpolarization due to more K+ leaving than Na+ entering cell due • Diffusion of Na/K gradually restores original RMP Figures distorted to demonstrate principles (figures 12.13b more true) Action Potentials (cont.) Action AP’s are all-or-none: stimulus strong enough to depolarize neuron stimulus to threshold, then cell fires @ SAME voltage spike to AP’s are nondecremental: don’t get weaker with distance AP’s are irreversible: AP goes to completion (can’t be stopped) Refractory period= prd of resistance to restimulation (smal...
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