Lecture1013final

Lecture1013final - The Neuromuscular junction was the...

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The Neuromuscular junction was the classic preparation for understanding the basis for synaptic transmission in experiments in the 1960’s by Katz, Miledi and collaborators. Nerve muscle preparation EPP is a graded potential whose amplitude is dependent on the Number of synaptic boutons activated and the conc. of Ca2+ in the extracellular fluid Generates a.p in presynaptic axon
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5.6 Synaptic transmission at the neuromuscular junction. (Part 2) Preparation bathed in low ca2+ soln , so that a.p’s cannot elicit much NT release . Spontaneous activity. Preparation bathed in normal Ca2+ , but unstimulated
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5.7 Quantized distribution of EPP amplitudes evoked in a low Ca 2+ solution. (Part 1)
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5.7 Distribution of MEPP amplitudes accounts for one quantal unit of the EPP amplitude distribution Conclude: EPP’s are made up from the summation of a number of quantal events The number of quantal events per EPP is random, and fluctuates from stimulation to stimulation according to the Poisson distribution The average size of a quantal event forming the EPP is the same as that of the MEPP. Supports a model in which the MEPP’s arise from the occassional random release of a single vesicles containing NT molecules. EPP’s arise from the concerted release of several vesicles at once, from a large pool. The total number released per stimulation is still somewhat random though
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5.8 Relationship of synaptic vesicle exocytosis and quantal transmitter release. (Part 1) P inhibits axonal potassium channels – prolongs the a.p. more vesicles re Freeze-fracture e.m. taken a few ms after stimulation Unstimulated Stimulated
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5.8 synaptic NT vesicles are held close to the Ca2+ channels by docking proteins – ready to fuse Ca channels Docked vesicles, Ready to fuse Fused vesicles
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5.3 Sequence of events involved in transmission at a typical chemical synapse
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Lecture1013final - The Neuromuscular junction was the...

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