Textbook Notes (368,432)
Canada (161,877)
Neuroscience (289)
NROB60H3 (151)
Chapter 5

Chapter 5: Synaptic Transmission

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Janelle Leboutillier

Chapter 5 Synaptic Transmission Introduction o Charles Sherrington named synapses o Synaptic transmission process of information transfer at a synapseo Electrical synapses proved by Furshpan and Potter o Chemical synapses proved by Otto Loewi showed release of chemical acetylcholine with electrical stimulation of axons innervating frog heart Kats showed that fast synapse of motor neuron and skeletal muscle was chemically mediatedEccles used glass microelectrode to study physiology of synaptic transmission in mammalian CNS indicated many CNS neurons use chemical transmission Types of Synapses o Presynaptic to target postsynaptic Electrical Synapses o Gap junction where electrical synapses occur membranes of two cells separate by about 3nm and gap is spanned by clusters of connexins6 form a connexon and two one from each cell forms a gap junction channel allowing passage of ions from cell to cell12nm diameter pore so major ions and small organic molecules can passCommon in early embryonic stages allows signals to control growth and maturationFound where activity of neurons is highly synchronized Also found between many non neuronal cells o Bidirectional can flow back and induce PSP in first neuron o Cells are electrically coupled o Fast and fail safe transmission o Occur in invertebrates for escape reflexes o Occur in vertebrate brain in every part of mammalian CNS o Post Synaptic Potential small 1mv caused by ion flow into the cellSeveral simultaneously can excite the neuron Chemical Synapses o Synaptic cleft separate presynaptic and postsynaptic2050nm wide filled with matrix of fibrous extracellular protein to make them adhere to one another o Presynaptic element axon terminal typically containing dozens of 50nm synaptic vesicles and some also 100nm secretory granulesdensecore vesicles containing dark soluble protein o Membrane differentiations dense accumulations of proteins adjacent to and within the membranes in either side of the synaptic cleft o Active zones site of neurotransmitter release pyramids and associated membranesSynaptic vesicles are in cytoplasm adjacent to active zones o Postsynaptic density protein thickly accumulated in and under postsynaptic membrane contains neurotransmitter receptors that convert intercellular signal to intracellular signal o CNS SynapsesAxodendritic if postsynaptic membrane is on dendriteAxosomatic if postsynaptic membrane is on cell bodyAxoaxonic if postsynaptic membrane is on another axonDendrodendritic synapses when dendrites synapse on dendrites
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