lecture 8 - chemical synaptic transmission 9_26_08v 10

lecture 8 - chemical synaptic transmission 9_26_08v 10 -...

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9/16/09 www.utexas.edu/neuroscience/Neurobiology/WesThompson Chemical Synaptic Transmission I
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9/16/09 Outline for Lecture 8 Review excitatory and inhibitory synapses EPSP and IPSP Summation Position of synapse on the neuron Review Reversal Potential Identification of Neurotransmitters Criteria for Neurotransmitters Acetylcholine and cholinergic synapses
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9/16/09 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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9/16/09 Excitatory neuron Inhibitory neuron ... -70 mv -75 mv Inject negative current + Pre-synaptic neuron Post-synaptic neuron
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9/16/09 + + + -70 mv 0 mv +55 mv threshol d Action potential 1 ms Action potential invades terminal + Presynaptic cell Post-synaptic cell Excitatory Synapse Positive charges carried by Na+ ions
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9/16/09 Action potential invades terminal _ _ _ -70 mv 0 mv +55 mv inhibition Presynaptic cell Post-synaptic cell Inhibitory Synapse Negative charges are carried by Cl ions _
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9/16/09 Spinal cord _ + + extensor muscle now contracts Flexor muscle relaxes because motor neuron that innervates it is inhibited!!!! Excites these neurons Inhibits this neuron
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9/16/09
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9/16/09 Response to E1 alone Response to E1 +E 2 alone Spatial summation of excitation Spatial summation of excitation and inhibition **** Keep this in mind ! **** At the end of the lecture today we will discuss presynaptic inhibition in the pain pathway. Response to E1 alone Response to E1 +E 2 alone
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9/16/09 Where the synapse on the neuron matters! 70 um from soma 700 um from cell body EPSP recorded in soma 0.2m V 0.03m V 0.2m V 7X as strong Nature Neuroscience 3 , 849 - 851 (2000) Distant synapses raise their voices Nelson Spruston The Efficiency that the signal is propagated depends on : branch points of the neuron ion channel that are expressed on the dendrites
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9/16/09 When channels on muscle fiber open due to binding of ACh molecules, which ions flow to generate the end-plate potential? ACh Receptors 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. Remember, the endplate potential is simply an EPSP at the neuromuscular junction.
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9/16/09 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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9/16/09 -15 mV -25 mV -40 mV -60 mV -75 mV 0 mV +15 mV +25 mV reversal potential Synaptic currents at the neuromuscular junction measured when the membrane potential was clamped to the values shown at left Membrane potential at which cell was clamped net inward currents net outward currents More Na + enters cell than K + leaves More K + leaves cell than Na + enters Amount of K + leaving cell equals amount of Na + entering cell More K+ leaves cell than Na+ enters More Na+ enters cell than K+ leaves
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