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Where does one often find gap junctions?
What links them? What is the
directionality and regulation? What can
they pass?
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-Often happen in cell bodies and
dendrites, or in astrocytes
-connected by connexins
-they can be gatable and bidirectional
-can pass current and small signalling
molecules
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Which types of cells can contain gap
junctions?
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Both neurons and glia (especially
astrocytes)
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How do most neurons signal?
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Through a chemical synapse. Release of transmitter causes a response in the postsynaptic cell
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What did Otto Loewi's experiment consist of?
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Stimulate the vagus nerve of the heart, then have the synapse in solution and wash the solution over a second heart.
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What were Loewi's findings?
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The second heart was affected in the same way as the first, simply by transferring a solution. This proves the presence of a chemical "vagusstoff" that acts
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What type of synapse was used to discover how the chemicals were released?
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The squid giant synapse
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What techniques were used on the squid giant synapse?
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Depolarization of the presynapse slowly until a postsynaptic response was seen, add TTX but depolarize at the synapse and signalling still occurs, also block K+ channels and Ca2+ channels to see which ion is needed
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What is needed for chemical release at the synapse? (ion)
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Ca2+ influx
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How important is presynaptic Ca2+ for transmitter release?
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It is completely necessary (and it is sufficient/ nothing else needed to signal)
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How was the importance of Ca2+ in transmitter release discovered?
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Block Ca2+ channels, also inject ca2+ to see if there is still a response (there was)
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What will happen to the postsynaptic membrane potential if a Ca2+ buffer is injected in the presynapse?
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The postsynaptic membrane potential will not change because the Ca2+ signalling has been prevented and therefore there was no transmitter release to bind to ionotropic receptors.
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Where are the Ca2+ channels located?
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They are located directly opposite the transmitter receptors in the synaptic cleft
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How is it possible to view the Ca2+ channels aligned with the receptors?
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Fluorescent conotoxins(Ca2+ channel blocker)and bungarotoxin(ACh receptor blocker)
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Name the 3 criteria that define a neurotransmitter:
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It must be present within the presynaptic neuron, It must be released in a depolarization and calcium dependent fashion, It must have specific receptors in the postsynaptic neuron.
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Which synapses in mammals are accessible for studying synapses (large)?
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NMJ (neuromuscular junction) synapses
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