Y khoa, y dược - The special senses: Part C

15 The Special Senses: Part CChemical SensesTaste and smell (olfaction) Their chemoreceptors respond to chemicals in aqueous solutionSense of SmellThe organ of smell—olfactory epithelium in the roof of the nasal cavity Olfactory receptor cells—bipolar neurons with radiating olfactory ciliaBundles 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 epitheliumFigure 15.21aOlfactory tractOlfactory bulb(a) NasalconchaeRoute ofinhaled airOlfactoryepitheliumFigure 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) Physiology of SmellDissolved odorants bind to receptor proteins in the olfactory cilium membranesA G protein mechanism is activated, which produces cAMP as a second messengercAMP opens Na+ and Ca2+ channels, causing depolarization of the receptor membrane that then triggers an action potentialOlfactory PathwayOlfactory receptor cells synapse with mitral cells in glomeruli of the olfactory bulbsMitral cells amplify, refine, and relay signals along the olfactory tracts to the:Olfactory cortex Hypothalamus, amygdala, and limbic systemFigure 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 channelGDPSense of TasteReceptor organs are taste buds Found on the tongueOn the tops of fungiform papillae On the side walls of foliate papillae and circumvallate (vallate) papillaeFigure 15.23a(a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae.Fungiform papillaeEpiglottisPalatine tonsilFoliate papillaeLingual tonsilFigure 15.23b(b) Enlarged section of a circumvallate papilla.Taste budCircumvallate papillaStructure of a Taste BudFlask shaped50–100 epithelial cells:Basal cells—dynamic stem cells Gustatory cells—taste cellsMicrovilli (gustatory hairs) project through a taste pore to the surface of the epitheliumFigure 15.23cTaste fibersof cranialnerveConnectivetissueGustatory(taste) cellsTasteporeGustatoryhairStratifiedsquamousepitheliumof tongue(c) Enlarged view of a taste bud.BasalcellsTaste SensationsThere are five basic taste sensationsSweet—sugars, saccharin, alcohol, and some amino acidsSour—hydrogen ionsSalt—metal ionsBitter—alkaloids such as quinine and nicotineUmami—amino acids glutamate and aspartatePhysiology of TasteIn order to be tasted, a chemical:Must be dissolved in salivaMust contact gustatory hairsBinding of the food chemical (tastant)Depolarizes the taste cell membrane, causing release of neurotransmitterInitiates a generator potential that elicits an action potentialTaste TransductionThe 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)Gustatory PathwayCranial nerves VII and IX carry impulses from taste buds to the solitary nucleus of the medullaImpulses then travel to the thalamus and from there fibers branch to the:Gustatory cortex in the insulaHypothalamus and limbic system (appreciation of taste)Figure 15.24Gustatory cortex(in insula)Thalamic nucleus(ventral posteromedialnucleus)PonsSolitary nucleus inmedulla oblongataFacial nerve (VII)Glossopharyngealnerve (IX)Vagus nerve (X)Influence of Other Sensations on TasteTaste is 80% smellThermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastesTemperature and texture enhance or detract from tasteThe Ear: Hearing and BalanceThree parts of the earExternal (outer) earMiddle ear (tympanic cavity)Internal (inner) earThe Ear: Hearing and BalanceExternal ear and middle ear are involved with hearingInternal ear (labyrinth) functions in both hearing and equilibriumReceptors for hearing and balance Respond to separate stimuliAre activated independentlyFigure 15.25aExternalacousticmeatusAuricle(pinna)(a) The three regions of the earHelixLobulePharyngotympanic(auditory) tubeTympanicmembraneExternalearMiddleearInternal ear(labyrinth)External EarThe auricle (pinna) is composed of:Helix (rim)Lobule (earlobe)External acoustic meatus (auditory canal)Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glandsExternal EarTympanic membrane (eardrum)Boundary between external and middle earsConnective tissue membrane that vibrates in response to soundTransfers sound energy to the bones of the middle ear Middle Ear A small, air-filled, mucosa-lined cavity in the temporal boneFlanked laterally by the eardrumFlanked medially by bony wall containing the oval (vestibular) and round (cochlear) windowsMiddle Ear Epitympanic recess—superior portion of the middle earPharyngotympanic (auditory) tube—connects the middle ear to the nasopharynxEqualizes pressure in the middle ear cavity with the external air pressureFigure 15.25bPharyngotympanic(auditory) tubeAuditoryossiclesEntrance to mastoidantrum in the epitympanic recessTympanic membraneSemicircularcanalsCochleaCochlearnerveVestibularnerveOval window(deep to stapes) Round windowIncu(anvil) Malleus(hammer) Stapes(stirrup) (b) Middle and internal earVestibuleEar OssiclesThree small bones in tympanic cavity: the malleus, incus, and stapesSuspended by ligaments and joined by synovial jointsTransmit vibratory motion of the eardrum to the oval windowTensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to the hearing receptors Figure 15.26Pharyngotym-panic tubeTensortympanimuscleTympanicmembrane(medial view)StapesMalleusViewSuperiorAnteriorLateralIncusEpitympanicrecessStapediusmuscleInternal EarBony labyrinthTortuous channels in the temporal boneThree parts: vestibule, semicircular canals, and cochlea Filled with perilymphSeries of membranous sacs within the bony labyrinthFilled with a potassium-rich endolymphFigure 15.27AnteriorSemicircularducts insemicircularcanalsPosteriorLateralCristae ampullaresin the membranousampullaeUtricle investibuleSaccule investibuleStapes inoval windowTemporalboneFacial nerveVestibularnerveSuperior vestibular ganglionInferior vestibular ganglionCochlearnerveMaculaeSpiral organ(of Corti)Cochlearductin cochleaRoundwindow VestibuleCentral egg-shaped cavity of the bony labyrinthContains two membranous sacsSaccule is continuous with the cochlear ductUtricle is continuous with the semicircular canalsThese sacsHouse equilibrium receptor regions (maculae)Respond to gravity and changes in the position of the headSemicircular CanalsThree canals (anterior, lateral, and posterior) that each define two-thirds of a circleMembranous semicircular ducts line each canal and communicate with the utricleAmpulla of each canal houses equilibrium receptor region called the crista ampullarisReceptors respond to angular (rotational) movements of the headFigure 15.27AnteriorSemicircularducts insemicircularcanalsPosteriorLateralCristae ampullaresin the membranousampullaeUtricle investibuleSaccule investibuleStapes inoval windowTemporalboneFacial nerveVestibularnerveSuperior vestibular ganglionInferior vestibular ganglionCochlearnerveMaculaeSpiral organ(of Corti)Cochlearductin cochleaRoundwindowThe CochleaA spiral, conical, bony chamberExtends from the vestibuleCoils around a bony pillar (modiolus)Contains the cochlear duct, which houses the spiral organ (of Corti) and ends at the cochlear apexThe CochleaThe cavity of the cochlea is divided into three chambersScala vestibuli—abuts the oval window, contains perilymphScala media (cochlear duct)—contains endolymphScala tympani—terminates at the round window; contains perilymphThe scalae tympani and vestibuli are continuous with each other at the helicotrema (apex)The CochleaThe “roof” of the cochlear duct is the vestibular membraneThe “floor” of the cochlear duct is composed of:The bony spiral laminaThe basilar membrane, which supports the organ of CortiThe cochlear branch of nerve VIII runs from the organ of Corti to the brain Figure 15.28a(a)HelicotremaModiolusCochlear nerve,division of thevestibulocochlearnerve (VIII)Cochlear duct(scala media)Spiral ganglionOsseous spiral laminaVestibular membraneFigure 15.28b(b)Cochlear duct(scala media;containsendolymph)Tectorial membraneVestibular membraneScalavestibuli(containsperilymph)Scala tympani(containsperilymph)BasilarmembraneSpiral organ(of Corti)StriavascularisSpiralganglionOsseous spiral laminaFigure 15.28c(c)Tectorial membraneInner hair cellOuter hair cellsHairs (stereocilia)Afferent nervefibersBasilarmembraneFibers ofcochlearnerveSupporting cellsFigure 15.28dInnerhaircellOuterhaircell(d)