Lecture 5 Synaptic Transmission web

Lecture 5 Synaptic Transmission web - Action Potential...

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Click to edit Master subtitle style Action Potential (continued) What happens after an action potential reaches the end of the axon?
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Significance of Voltage Clamp working hypothesis, mid 1900s: at threshold, voltage-dependent increase in gNa is involved in Difficult to test this hypothesis since Vm & conductance ______ _______ during an AP Voltage clamp amplifier holds Vm constant despite ________________in gNa & gK while measuring Iions This allowed measurement of gNa & gK at a ______ 1. gNa rapidly increases with steep relationship on Vm > threshold 2. gNa rapidly decreases after a slight delay even when Vm >> threshold 3. gK increases after a slight delay with steep relationship to Vm gK does not decrease if Vm is held at a level above threshold
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Patch Clamp Technique Patch clamp technique measures current through a ______ ion channel. Sensitive amplifier connected to glass pipette with tiny opening. Tight contact between glass pipette and membrane achieved with suction. Membrane potential controlled to study voltage dependence of current through _____ ion channel. Current is ~1 to 2 pA (10-12 ampere). Several orders of magnitude smaller than current measured by voltage clamping entire _____
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Patch-clamp recording of voltage-gated ____channel Properties of voltage-gated ____channels explain action potential properties Vm depolarized to threshold, -40 mV → ↑chance of opening Channels open soon after depolarization – thus rapid rising phase Channels inactivate quickly – thus brief action potential duration _____________needed to relieve inactivation – explains __________ period
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Averaged current recorded from many single ____channels has same time course as ‘macroscopic’ ____current (current recorded from whole axon by traditional voltage clamp method)
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Voltage-gated potassium channels contribute to falling phase Help bring ___ back to resting membrane potential after peak of action potential: also known as ‘_________ rectifier channels’ Do not open immediately upon depolarization: delay allows open ____channels to take ___ to _____ of action potential Averaged current from many single openings has same time course as macroscopic K+ current
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Summary: How voltage- gated Na+ and K+ channels produce an action potential ____channels open soon after depolarization Inward current through ____ channels Rapid ___influx brings Vm close to ____ ___channels inactivate quickly ___channels open with a _____ __ efflux brings Vm back to resting membrane potential, close to __ The undershoot is explained by increased gK compared to rest, ___ briefly dips below resting membrane potential
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Action potential ___________ down axon Positive charges entering during AP spread and cause membrane just ahead to depolarize to threshold, resulting in a new AP AP normally _________ in ___ direction because membrane behind it is refractory because Na+ channels are still inactivated
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Lecture 5 Synaptic Transmission web - Action Potential...

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