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Chapter 5

Chapter 5 - ST

6 Pages

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Janelle Leboutillier

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Chapter 5Synaptic Transmission 135166 Introduction Synaptic Transmission Process of information transfer at a synapseSynapse Area where one neuron transfers information to another at this specialized areaExistence of electrical synapses proven in 1959 when Rushpan and Potter studied NS of crayfishelectrical synapses are common in mammalian brainAlternative hypothesis about nature of synaptic transmission was that chemical neurotransmitters transfer information form 1 neuron to another at the synapseConcept of chemical synapses was by Loewi which showed that electrical stimulation fo axons innervating the frogs hear cause the release of chemical and that this chemical could mimic the effects of neuron stimulation on the heartbeat New method of studying the molecules involved in synaptic transmission have revealed that synapses are far more complex than most neuroscientists anticipatedBox 51 Otto Loewi and Vagusstoff 137 Types of SynapsesInformation tends to flow in 1 direction form a neuron to target cell st 1 cell is presynaptic and target cell is postsynaptic Electrical SynapsesGap JunctionsElectrical synapses occur at specialized sites membranes of 2 cells are separated by 2 nm and is spanned by clusters of special proteins calledconnexions 6 connexins make channel called connexon 2 connexons combine to form gap junction channel allows ions to pass directly from cytoplasm of 1 cell to cytoplasm of anotherGap Junctions allow ionic current to pass equally well in both directionselectrical synapses are bidirectional Gap junctions are said to be electrically coupled electrical current can pass through these channelsElectrical synapses also occur in vertebrate brainAP in presynaptic neuron can produce AP in post synaptic neuronElectrical synapses also occur in vertebrate brainAP of presynaptic channel causes a small amount of ionic current to pass through GJ to other neuronPOSTSYNAPTIC POTENTIAL PSPRoles of electrical synapses vary from 1 brain region to another common during early embryonic stages allow neighbouring cells to share electrical and chemical signals and also interconnect nonneural cells epithelial cells smooth and cardiac muscle cells liver cells and some glandular cellsChemical Synapses Presynaptic and postsynaptic membranes at chemical synapses are separated by synaptic cleft field with matrix of fibrous extracellular matrix to adhere to one anotherPresynaptic side of synapses called presynaptic element is axon terminal contain s 12s of small membraneenclosed spheres called synaptic vesicles store NTLarger vesicles are called secretory granules contain soluble protein that appears darkin electron microscopes so they are sometimes called large densecore vesicles
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