BIO2A03-2011-L23 - B iology 2A03 2009 L ect ur e 23 T he tr...

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Biology 2A03 - 2009 Lecture 23
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The “traditional view” was that n/ t release followed the all-or-none law - that one A.P. always released the same amount of n/ t, and thereby created the same size G.P. at post-synaptic membrane. We now know this is over-simplistic ==> many exceptions: - autoreceptors on pre-synaptic membrane may down-regulate subsequent n/ t release. - multiple transmissions may temporarily exhaust synaptic vesicles of n/ t. - desensitization or loss of post-synaptic receptor proteins may occur in response to multiple transmissions. - upregulation of n/ t release and/ or post-synaptic receptor density may occur in frequently used or rarely used (!) pathways . - presynaptic inhibition or facilitation of n/ t release may occur via axo-axonic synapses . ===> frequency code is greatly modified at chemical synapses
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Transmissions at axo-axonic synapses may modify n/ t release Presynaptic inhibition
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The “traditional view” that synapses followed the All-or-None Law arose because all the early research on synapses was done on one of the largest synapses – the neuromuscular junction - where this is true (Fatt, Katz, & Miledi - Nobel Prize).
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