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Lecture 5

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University of Toronto St. George
Doug Mac Kay

05 Receptor PotentialSeptember 19 2007Receptor potentialAction potentials start at sensory organs that detect different energiesgenerate receptor potential oCauses depolarization of sensory receptors upon receipt of specific energy eg light heat pressure etcoEXCEPTIONphotoreceptors hyperpolarize increase polarityReceptor proteinReceptor protein is embedded in sensory cell membranechanges shape when specific energy receivedcauses one of two things to happeno1 cation channel openo2 an enzyme is activated via Gprotein coupling enzyme reactionsthis mechanism is slower than opening cation channel because of the chain of metabolic reactionsGprotein and enzyme activations amplify weak signalssensitive to single stimulus moleculesstimulated receptor repeatedly activates Gprotein by triggering exchange of GDP b GTP on subunitsmultiple subunits dissociate and activate nd adenylyl cyclase to make cAMP 2messenger from ATPocAMP phosphorylates membrane proteins or gate ion channels to 2 allow influx of Na and Caand cause depolarizationex chemoreceptors olfactory system can ndgenerate lots of 2 messengers from one molecule to generate a big receptor potential1 sensory membrane can be the end of an axonaxon terminals have receptors embedded in themoex mechanoreceptors stretched from spinal cord to skindetect pressure which distorts the membrane to open ion channels to create a depolarizing receptor potentialosensory membrane axon terminal is inexcitableosome receptor potential is distorted2 can use specialized sensory cellsoex chemoreceptor taste receptor on tonguehave microvilli that have receptorssome receptors are Gprotein couples and others are cation channelsdepolarizing potention spreads through entire cell 2causes influx of Ca at a synapse with an axon and triggers exocytosis and neurotransmitters are released which bind to postsynaptic receptorspostsynaptic potentials are generated on the postsynaptic membraneno action potentials generated1
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