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Chapter 8.docx

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University of Toronto Scarborough
Matthias Niemeier

Chapter 8The Chemical Senses285 to 308IntroductionLife evolve in a sea of chemicalsThe most familiar of chemical senses tastegestation and smellMany types of chemically sensitive cellschemoreceptorsdistributed throughout bodyGustation and olfaction serve to detect environmental chemicalsTasteHumans evolved as omnivores Latin omnisall vorareto eat eating plants and animalsThe Basic TastesWe only recognize basic taste5Saltiness sourness acidsH sweetness sucrose bitterness simple ionsK and Mg for complex organic molecules like caffeine umami MSGEach food activates different combination of basic tastes and distinctive flavour as result of taste and smellOrgans of TasteTongue palate pharynx and epiglottisOdors from food can also pas from pharynx to nasal cavityPapillae Latin bumps Shaped like ridges foliate papillae pimples vallate papillae or mushrooms fungiform papillaeTaste Buds contains 50150 taste receptor cellstaste cells wI bud epithelium also has basal cells that surround taste cellsUsually 20005000 taste budsTaste Receptor CellsChemically sensitive part of taste receptor cell is small membrane regions called apical end near surface of tonguehave thin extensions called microvilliWhen taste receptor cell is activated by chemicalmembrane potential changes depolarizingreceptor potential if depolarizing and large enough most taste receptor cells cause vgated Ca channel to openCa enters cytoplasmto trigger release of transmitter moleculesMechanisms of Taste TransductionTransduction Latin transducere to lead across Stimulus causes an electrical response in a sensory receptor cellTaste transduction involves several different processes taste stimuli may 1 Directly pass through ion channels salt and sour 2 bind to and block ion channels sour or 3 bind to Gproteincoupled receptors in membrane that ndactivate 2 messenger systems that open ion channels bitter sweet and umami
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