15Chemical SensesSense of SmellSlide 4Slide 5Physiology of SmellOlfactory PathwaySlide 8Sense of TasteSlide 10Slide 11Structure of a Taste BudSlide 13Taste SensationsPhysiology of TasteTaste TransductionGustatory PathwaySlide 18Influence of Other Sensations on TasteThe Ear: Hearing and BalanceSlide 21Slide 22External EarSlide 24Middle EarSlide 26Slide 27Ear OssiclesSlide 29Internal EarSlide 31VestibuleSemicircular CanalsSlide 34The CochleaSlide 36Slide 37Slide 38Slide 39Slide 40Slide 41PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal CollegeC H A P T E RCopyright © 2010 Pearson Education, Inc.15 The Special Senses: Part CCopyright © 2010 Pearson Education, Inc.Chemical Senses•Taste and smell (olfaction) •Their chemoreceptors respond to chemicals in aqueous solutionCopyright © 2010 Pearson Education, Inc.Sense of Smell•The organ of smell—olfactory epithelium in the roof of the nasal cavity •Olfactory receptor cells—bipolar neurons with radiating olfactory cilia•Bundles of axons of olfactory receptor cells form the filaments of the olfactory nerve (cranial nerve I)•Supporting cells surround and cushion olfactory receptor cells •Basal cells lie at the base of the epitheliumCopyright © 2010 Pearson Education, Inc.Figure 15.21aOlfactory tractOlfactory bulb(a) NasalconchaeRoute ofinhaled airOlfactoryepitheliumCopyright © 2010 Pearson Education, Inc.Figure 15.21aMitral cell (output cell)OlfactoryglandOlfactorytractOlfactoryepitheliumFilaments of olfactory nerveCribriform plate of ethmoid boneLamina propria connective tissueBasal cellSupporting cellDendriteOlfactory ciliaOlfactory bulbGlomeruliAxonOlfactory receptor cellMucusRoute of inhaled aircontaining odor molecules(b)Copyright © 2010 Pearson Education, Inc.Physiology of Smell•Dissolved odorants bind to receptor proteins in the olfactory cilium membranes•A G protein mechanism is activated, which produces cAMP as a second messenger•cAMP opens Na+ and Ca2+ channels, causing depolarization of the receptor membrane that then triggers an action potentialCopyright © 2010 Pearson Education, Inc.Olfactory Pathway•Olfactory receptor cells synapse with mitral cells in glomeruli of the olfactory bulbs•Mitral cells amplify, refine, and relay signals along the olfactory tracts to the:•Olfactory cortex •Hypothalamus, amygdala, and limbic systemCopyright © 2010 Pearson Education, Inc.Figure 15.2212 Odorant bindsto its receptor. Receptoractivates G protein (Golf).3 G proteinactivates adenylate cyclase.4 Adenylatecyclase converts ATP to cAMP.5 cAMP opens a cation channel allowing Na+ and Ca2+ influx and causing depolarization.OdorantG protein (Golf)ReceptorAdenylate cyclaseOpencAMP-gatedcation channelGDPCopyright © 2010 Pearson Education, Inc.Sense of Taste•Receptor organs are taste buds •Found on the tongue•On the tops of fungiform papillae •On the side walls of foliate papillae and circumvallate (vallate) papillaeCopyright © 2010 Pearson Education, Inc.Figure 15.23a(a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae.Fungiform papillaeEpiglottisPalatine tonsilFoliate papillaeLingual tonsilCopyright © 2010 Pearson Education, Inc.Figure 15.23b(b) Enlarged section of a circumvallate papilla.Taste budCircumvallate papillaCopyright © 2010 Pearson Education, Inc.Structure of a Taste Bud•Flask shaped•50–100 epithelial cells:•Basal cells—dynamic stem cells •Gustatory cells—taste cells•Microvilli (gustatory hairs) project through a taste pore to the surface of the epitheliumCopyright © 2010 Pearson Education, Inc.Figure 15.23cTaste fibersof cranialnerveConnectivetissueGustatory(taste) cellsTasteporeGustatoryhairStratifiedsquamousepitheliumof tongue(c) Enlarged view of a taste bud.BasalcellsCopyright © 2010 Pearson Education, Inc.Taste Sensations•There are five basic taste sensations1. Sweet—sugars, saccharin, alcohol, and some amino acids2. Sour—hydrogen ions3. Salt—metal ions4. Bitter—alkaloids such as quinine and nicotine5. Umami—amino acids glutamate and aspartateCopyright © 2010 Pearson Education, Inc.Physiology of Taste•In order to be tasted, a chemical:•Must be dissolved in saliva•Must contact gustatory hairs•Binding of the food chemical (tastant)•Depolarizes the taste cell membrane, causing release of neurotransmitter•Initiates a generator potential that elicits an action potentialCopyright © 2010 Pearson Education, Inc.Taste Transduction•The stimulus energy of taste causes gustatory cell depolarization by:•Na+ influx in salty tastes (directly causes depolarization)•H+ in sour tastes (by opening cation channels)•G protein gustducin in sweet, bitter, and umami tastes (leads to release of Ca2+ from intracellular stores, which causes opening of cation channels in the plasma membrane)Copyright © 2010 Pearson Education, Inc.Gustatory Pathway•Cranial nerves VII and IX carry impulses from taste buds to the solitary nucleus of the medulla•Impulses then travel to the thalamus and from there fibers branch to the:•Gustatory cortex in the insula•Hypothalamus and limbic system (appreciation of taste)Copyright © 2010 Pearson Education, Inc.Figure 15.24Gustatory cortex(in insula)Thalamic nucleus(ventral posteromedialnucleus)PonsSolitary nucleus inmedulla oblongataFacial nerve (VII)Glossopharyngealnerve (IX)Vagus nerve (X)Copyright © 2010 Pearson Education, Inc.Influence of Other Sensations on Taste•Taste is 80% smell•Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastes•Temperature and texture enhance or detract from tasteCopyright © 2010 Pearson Education, Inc.The Ear: Hearing and Balance•Three parts of the ear1. External (outer) ear2. Middle ear (tympanic cavity)3. Internal (inner) earCopyright © 2010 Pearson Education, Inc.The Ear: Hearing and Balance•External ear and middle ear are involved with hearing•Internal ear (labyrinth) functions in both hearing and equilibrium•Receptors for hearing and balance •Respond to separate stimuli•Are activated independentlyCopyright © 2010 Pearson Education, Inc.Figure 15.25aExternalacousticmeatusAuricle(pinna)(a) The three regions of the earHelixLobulePharyngotympanic(auditory) tubeTympanicmembraneExternalearMiddleearInternal ear(labyrinth)Copyright © 2010 Pearson Education, Inc.External Ear•The auricle (pinna) is composed of:•Helix (rim)•Lobule (earlobe)•External acoustic meatus (auditory