Lecture 2A - Binding of 3 Na+ ions Energy input of ATP...

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Binding of 3 Na + ions + out and bringing 2 K + in.
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Myelin allows AP to propagate faster than it would in an unmyelinated axon. Current is continually leaking out, so need more Na + channel clusters closer together.
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Myelin acts like an insulator that defense the continual leakage of positive charge out of axon, into extracellular space. Myelin makes it so that there’re only discrete points where it has to have activation of voltage-gated Na + channels. Opening of these channels, reconstituting AP takes time. Can have clusters spread further apart b/c myelin insulation is preventing leakage of positive current out of axon. The depolarization at the resultant travels bidirectionally, but the inactivation of voltage-gated Na + channels prevents AP from being reconstituted in the place that it just previously was. Voltage-gated Na + channels undergoing refractory period are useless in propagating another AP AP moves in one direction instead of bouncing back & forth along the length of axon.
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Structure & function of 2 types of synapses: electrical & chemical synapse Axonal transport from cell body to synaptic terminal of 2 general classes of neurotransmitter Quantal release of small discrete packets of NT from membrane-bound vesicles Exocytosis – release of transmitter Endocytosis – recycling of vesicles that was released
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It was known that stimulation of vagus (one of cranial nerves) could slow down rate. He postulated that the vagus which synapse w/ heart, releases chemical onto heart muscles that causes beat to slow down. Experiment: o Removed ♥’ s of 2 frogs. 1 st nd beaker connected by a tube w/ another frog ♥. o When he provided stimulation to nerve (in record), 1 st beat slowed down within a few seconds. A short time later, HR of 2 nd heart also slowed down indicating that there’s substance that traveled from beaker 1 to 2 to facilitate the slowing of 2 nd . Chemical released by vagus nerve is the common NT acetylcholine. Loewi’s experiment was the first description of chemical synaptic transmission
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Synapse – where a presynaptic neuron interface w/ a postsynaptic neuron (close contact between 2 neurons). Electrical synapse o There’s a physical contact between cells. o Within electrical synapse are membrane channels that oppose one another perfectly so there’re continuous opened pores from presynaptic membrane of neuron to postsynaptic membrane of 2 nd neuron. These pores/channels are called gap junction channels, which allow direct flow of ions from one neuron to the other. Chemical synapse
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Lecture 2A - Binding of 3 Na+ ions Energy input of ATP...

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