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Chapter 5

Chapter 5 Notes

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Janelle Leboutillier

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Chapter 5 Notes Synaptic Transmission: the process of information transfer a synapse Electrical Synapse: One hypothesis of synaptic transmission whereby electrical current flowed from one neuron to the next Chemical Synapses: Another hypothesis of synaptic transmission whereby chemical neurotransmitters transfer information from on neuron to another at the synapse - Supported by Otto Loewi o Electrically stimulated axons which innervated the frogs heart caused the release of a chemical and this chemical could mimic the effects of neuron stimulation of the heart beat o Proved that synaptic transmission between nerve and heart is chemically mediated o Heart is supplied with two types of innervation; one type speeds the beating of the heart, the other slows (supplied by the vagus nerve) o Isolated a frog heart with the vagal innervation left intact, stimulated the nerve electrically and observed the expected effect, the slowing of the heartbeat The critical demonstration that this effect was chemically mediated came when he took the solution that bathe this heart, applied it to a second isolated frog heart applied it to a second isolated frog heart, and found that the beat of this one also slowed Neurotransmitter here termed vagusstoff turned out to be acetylecholine o Chemical synapses comprise the majority of synapses in the brain Synapse: Specialized junction where one part of a neuron contacts and communicates with another neuron or cell type (such as muscle or glandular cell) - Information flows in one direction (from neuron to target cell) Electrical Synapses - Simple in structure and function and allow direct transfer of ionic current from one cell to the next - Occur at gap junctions membranes of two cells are separated by only 3mm o Gap is spanned by special proteins called connexins o Six connexins combine to form a channel (connexon) and two connexons (on from each cell) combine to form a gap junction channel Channel allows ions to pass directly from the cytoplasm of one cell to the cytoplasm of the other Pore of most gap junction channels is large: 1-2nm which is big enough for all major cellular ions and many small organic molecules to pass through o Electrical synapses are bidirectional, transmission is very fast, fail-safe o An AP in the presynaptic neuron can produce an AP in the postsynaptic neuron almost instantaneously - Electrical synapses are common in every part of the mammalian CNS - When two neurons are electrically coupled, an AP in the presynaptic neuron causes a small amount of ionic current to flow across the gap junction channels into the other neuron o This current causes a postsynaptic potential (PSP) in the second neuron (and therefore induces a PSP in the first neuron) www.notesolution.com
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