Action Potential Generation Initiation of AP? threshold? Rising - - PowerPoint PPT Presentation

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Sep 13, 2022 186 likes •410 views

Action Potential Generation Initiation of AP? threshold? Rising phase? Falling phase? All happening in 1 msec! Current across membrane I m = I Rm + I Cm Examples of passive voltages Initiating AP?? AP spread ahead Receptor potentials

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Initiation of AP? threshold? Rising phase? Falling phase? All happening in 1 msec!

Action Potential Generation

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Current across membrane Im = I Rm + ICm Examples of passive voltages Initiating AP?? AP spread ahead Receptor potentials Synaptic potentials

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Typical values 0.01 to 1.0 mm. Experimental measurement of space constant

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Evolution of fast signal conduction

Reduce internal resistance to current flow Increase membrane resistance to leak current flow

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Lambda and tau interact to determine speed and amplitude

f voltage change ahead of AP

Tau 1-20 ms

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Initiation Na vs K Na wins Threshold- dynamic Again Na vs K Fall- K

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Traveling AP- unmyelinated nerve Local current flowing ahead of AP initiates next AP What happens first?- Spreading charge depolarizes Cm. 1 ms!

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Also: Cs in series add reciprocally Traveling AP- myelinated nerve Comparison of traveling AP

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Repolarization at Nodes of Ranvier by fast tau for repolarization unmyelinated nerve resting g= 0.2-1 mS/cm2, tau 1-20 ms myelinated nodes resting g= 40 mS/cm, tau= 100S! Traveling AP- myelinated nerve

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AP conduction velocity: Squid giant axon vs. myelinated nerve

19 m/s = 43 mph 500 micron

Alpha motor neuron: 120 m/s = 268 mph 8.6 microns Unmelyinated C pain fibers: 2m/s = 4 mph 1.5 micron Same as 10 micron Frog myelinated fiber!!

Squid Mammal

Nerves

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Refractory periods

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Why doesn’t the AP go backwards?

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Vr stable Vth unstable Vpeak could be stable but conductances are time and V sensitive I/V curve explanation for AP

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Refractory periods D- gK>>>gNa C- gNa recovering, but no AP B- smaller AP A- full AP Notice threshold change

C,D A B

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Add Ca to the equation Calcium APs

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Examples of calcium APs

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Na vs. Ca AP

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Calcium current contributing to APs

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Calcium current inactivation

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Ca-activated K current

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Na AP vs. Heart AP

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