Lecture 7.F10

Lecture 7.F10 - Neuroscience 106: Lecture 7 - Postsynaptic...

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Neuroscience 106: Lecture 7 - Postsynaptic Potentials (PSPs) continued ANNOUNCEMENTS: 1. In Bear et al. study Chapter 6. 2. For the Midterm Thursday Oct. 28th: A. Read Chapters 1 and 7. B. Study Chapters 2, 3, 4, 5, 6 (especially Chapters 3-6). C. Study the "Membrane Potentials Worksheet" - there will be a quiz in discussion for extra credit on the midterm. TODAY'S LECTURE: POSTSYNAPTIC POTENTIALS (cont.) I. Postsynaptic potentials (PSPs) A. Synaptic potentials are computational (or decision-making) mechanisms. They decide whether or not the neuron will generate an action potential. II. Postsynaptic potentials (PSPs) versus action potentials: A. PSPs differ categorically from action potentials in every way . 1. For example, PSPs have no refractory period and action potentials do. 2. For example, PSPs are graded in amplitude and duration and action potentials are stereotyped. B. Some reasons why PSPs and action potentials differ: 1. PSPs have no refractory period because they are generated by the opening of neurotransmitter-gated channels in the membrane of the soma and dendrites and ligand-gated ion channels have no inactivation gate . 2. PSPs are graded in amplitude because they are generated by the opening of neurotransmitter-gated ion channels and more neurotransmitter released from the 1
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presynaptic terminal opens more channels. There is no inactivation-gate to prevent this. III. Mechanisms for the production of EPSPs A. EPSPs are generated by the opening of neurotransmitter-gated Na + /K + ion channels. B. The maximum depolarization for the EPSP is to -9 mV . This is because -9 mV is the average of the equilibrium potentials of Na + and K + , the two ions to which the membrane becomes equally permeable. C. Below is a figure demonstrating how opening Na + /K + ion channels drives the membrane potential towards -9 mV (the reversal potential) no matter what the starting voltage is: In this diagram: The depolarization is caused predominantly by an influx of Na + . The hyperpolarization is caused predominantly by an efflux of K + . The reversal potential is the voltage at which the dominant flow of ions changes (aka reverses) direction. If the channel is permeable to only one ion, then the reversal potential would equal the equilibrium potential for that ion. D. The figure below shows how the driving forces on sodium and potassium at -65 mV results in a greater sodium influx than potassium efflux, thus causing depolarization.
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Lecture 7.F10 - Neuroscience 106: Lecture 7 - Postsynaptic...

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