Lecture 8-synaptic transmission II

Lecture 8-synaptic transmission II - Lecture Today 1 Review...

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1 Lecture Today 1) Review basic features of synaptic transmission 2) Review reversal potential caused by release of transmitter 3) Consider the quantal hypothesis for transmitter release 4) Discuss the roles of calcium and how it causes the release of transmitter from the presynaptic axon 5) Introduce the idea of vesicle recyling
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2 AP starts here Release of neurotransmitter Excitatory neuron Inhibitory neuron . . . + + + + + + + + + Transmitter binds to receptors, opens channels and allows positive Na+ ions to flow into neuron Inject + current + Pre-synaptic neuron Post-synaptic neuron
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3 Excitatory neuron Inhibitory neuron ... -70 mv -75 mv Inject negative current + Pre-synaptic neuron Post-synaptic neuron
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4 Action potential Influx of ions shown as red balls
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5 Basal lamina Neuromuscular junction (NMJ) is the synapse that a motoneuron makes with a skeletal muscle fiber The transmitter used at all NMJs is acetylcholine (ACh).
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6 nerve Axon that innervates muscle fiber end plate Muscle fiber
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7 ACh (acetylcholine) is always released from axon terminal. ACh opens channels that excite skeletal muscle fibers and generates an action potential in the muscle fiber Action potential recorded in muscle fiber End plate The excitatory post-synaptic potential in muscle fibers also has a special name: the end-plate potential or EPP
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8 First question that we address is: When channels on muscle fiber open due to binding of ACh molecules, which ions flow to generate the end-plate potential? The answer is that the channels are equally permeable to both Na+ and K+. The permeability of the ACh receptors can be determined by evaluating the “reversal potential ” evoked by ACh.
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9 Reversal potential is determined by voltage clamping the membrane to various membrane potentials while stimulating the motoneuron and causing it to release ACh. The membrane potential (Vm) at which the current reverses from inward to outward (or outward to inward) is the reversal potential.
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