3 neuronal signals 2 - action potentials - lecture slides

3 neuronal signals 2 - action potentials - lecture slides -...

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Signaling Within & Between Nerve Cells The Action Potential Neurophysiology University of Colorado at Boulder Department of Integrative Physiology
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Steps to Learning Goal ± Ionic basis of the action potential voltage-gated ion channels positive feedback loops ± Voltage clamp technique membrane currents and conductances during the action potential ± Threshold – converting local, graded potentials into action potentials ± Refractory periods Firing properties of neurons vary
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Recommended Reading ± From Kandel et al. (2000) Principles of Neuroscience Chapter 9: Propagated Signaling- The Action Potential, pp. 150-169
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The Action Potential (1) ± Nerve cells are able to carry signals over long distances because of their ability to generate an action potential . ± An action potential consists of several phases resulting from the sequential opening & closing of voltage-gated ion channels. Afterhyperpolarization Return to V rest Peak
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Channel Characteristics (2) ± Opening of both voltage- gated Na + & K + channels is voltage-dependent. Voltage-gated Na + channels open more rapidly than do K + channels ± Number of channels that open (& change in conductance) depends on magnitude of change in membrane potential. Depolarization increases the probability that a channel opens. =100%
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Na + Channel Inactivation (3) ± Voltage-gated Na + channels undergo inactivation ; this is a time-dependent process. In this state, the channels are closed, but inactivatable. Inactivation can only be removed by repolarization of the membrane, which allows channels to return to a resting state. • This switch takes time (a few milliseconds).
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Voltage-Clamp Technique (4) ± Voltage clamp is a negative feedback technique that allows experimenter to “clamp” membrane potential (V m ) at predetermined levels (command potential, CP) & measure membrane currents (I m ) that flow at that potential. ± Note: patch clamp is a refinement of the voltage clamp. ± Voltage-clamp makes it possible to determine the effect of V m on membrane conductance for different ions. ¾ How? First, voltage clamp is a current generator.
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Voltage-Clamp Technique: Keep Vm at CP (5a) Vm-CP=0? ± Voltage-clamp detects when V m -CP 0, and injects current into the cell to counteract the current flowing through voltage- gated channels.
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This note was uploaded on 02/27/2008 for the course IPHY 4720 taught by Professor Casagrand during the Fall '07 term at Colorado.

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3 neuronal signals 2 - action potentials - lecture slides -...

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