101_11AI-neuro5-synapses

101_11AI-neuro5-synapses - past few days 1) how single...

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past few days 1) how single neurons can produce spikes 2) how spikes propagate from axon hillocks to axon terminals today, topic set #5: chemical synapses Q: what happens at the axon terminal ? A: consider the structure & function of chemical synapses in particular… how does the axon terminal membrane potential change? how does this affect neurotransmitter release? how does this affect the membrane potential of target cells? npb101-w2011-ishida structure All neurons release a neurotransmitter onto a target cell (or a neurohormone into the blood). The site of transmitter release, diffusion, and binding to the target cell is called a chemical synapse . The transmitter-releasing cell is the pre-synaptic cell . The target cell is the post-synaptic cell . The target cell can be a neuron, muscle, or epithelial cell. Fig 4-20 chemical synapse
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Fig 4-20 note: cells are separated by a ‘cleft’ this is 1 of several ways cells communicate. this happens at different cellular connections a) direct b) short-range c) medium-range (paracrine) d) long-range (hormonal) npb101-w2011-ishida 1) how to increase neurotransmitter release 2) effect of transmitter on post-synaptic neurons a) when there’s one presynaptic cell b) when there’s more than one presynaptic cell 3) “response” to a decrease in transmitter release 4) how to stop the effect of transmitters 5) synapses without transmitters (“gap junctions”) 6) neurohormones (release into the blood, so not a synapse) to understand how this works, we will learn… this will allow us to examine functional interactions in efferent and afferent pathways
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if target cell is a neuron, there are often many synapses on that neuron. ‘many’ = 100 – 100,000 location: mostly (if not exclusively) on dendrites examples: ( left ) textbook Fig 4-14. ( right ) bipolar cell ribbon synapse markers onto a single LY-filled retinal ganglion cell merge onto dendrites !" $% & '()* +,"-(. Fig 4-14 npb101-w2011-ishida convergence : the presence of more than one synapse onto a neuron. the multiple pre-synaptic inputs are said to “converge” onto the post- synaptic cell. divergence : when a single pre- synaptic cell forms synapses onto more than one post- synaptic cell. the outputs is the single cell “diverge” to multiple post-synaptic cell. Fig 4-19
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reminder: 1) compare the size of neurons & other cells of the body 2) then think of fitting several thousands of synapses onto the dendrites of a neuron ! not in Sherwood npb101-w2011-ishida internal structure of a chemical synapse. .. from early 1970’s see Fig 4-15 Silverthorn 2010 Human Physiology Fig 8-20
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internal structure of a chemical synapse. .. more recent views Feng 09 Nat Rev Neurosci Ziv 04 Nat Rev Neurosci npb101-w2011-ishida neurotransmitter release Fig 4-15 1) depolarization of axon terminal 2) Ca 2+ influx thru voltage-gated Ca channels [Ca] o is 2-3 mM, resting [Ca] i is ~ 100 nM so, influx raises [Ca] i to μ M 3) rise in [Ca] i leads to exocytosis of vesicles 4) transmitter diffuses across cleft & binds to receptors 5) this leads to gating (opening or closing) of channels in the postsynaptic cell -- by allosteric effects or signaling cascades.
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101_11AI-neuro5-synapses - past few days 1) how single...

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