Special SensesChemical SensesTaste BudsSlide 4Anatomy of a Taste BudTaste SensationsTaste TransductionSense of SmellSlide 9Physiology of SmellOlfactory PathwayOlfactory Transduction ProcessEye and Associated StructuresEyebrowsPalpebrae (Eyelids)Lacrimal ApparatusSlide 17Structure of the EyeballSlide 19Vascular Tunic: Ciliary BodyVascular Tunic: IrisSensory Tunic: RetinaSlide 23The Retina: Ganglion Cells and the Optic DiscSlide 25The Retina: PhotoreceptorsInner Chambers and FluidsLightSlide 29Focusing Light on the RetinaFocusing for Distant VisionFocusing for Close VisionPhotoreception: Functional Anatomy of PhotoreceptorsSlide 34RodsConesCones and RodsChemistry of Visual PigmentsExcitation of RodsSlide 40Excitation of ConesPhototransductionSlide 43Copyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsSpecial SensesSpecial senses – Taste, Smell and VisionCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsChemical SensesChemical senses – gustation (taste) and olfaction (smell) Their chemoreceptors respond to chemicals in aqueous solutionTaste – to substances dissolved in salivaSmell – to substances dissolved in fluids of the nasal membranesCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsTaste BudsMost of the 10,000 or so taste buds are found on the tongueTaste buds are found in papillae of the tongue mucosaPapillae come in three types: filiform, fungiform, and circumvallateFungiform and circumvallate papillae contain taste budsCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsTaste BudsFigure 15.1Copyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsAnatomy of a Taste BudEach gourd-shaped taste bud consists of three major cell typesSupporting cells – insulate the receptor Basal cells – dynamic stem cells Gustatory cells – taste cellsCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsTaste SensationsThere are five basic taste sensationsSweet – sugars, saccharin, alcohol, and some amino acidsSalt – metal ionsSour – hydrogen ionsBitter – alkaloids such as quinine and nicotineUmami – elicited by the amino acid glutamateCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsTaste TransductionThe stimulus energy of taste is converted into a nerve impulse by:Na+ influx in salty tastesH+ in sour tastes (by directly entering the cell, by opening cation channels, or by blockade of K+ channels)Gustducin in sweet and bitter tastesCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsSense of SmellThe organ of smell is the olfactory epithelium, which covers the superior nasal concha Olfactory receptor cells are bipolar neurons with radiating olfactory ciliaOlfactory receptors are surrounded and cushioned by supporting cellsBasal cells lie at the base of the epitheliumCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsSense of SmellFigure 15.3Copyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsPhysiology of SmellOlfactory receptors respond to several different odor-causing chemicalsWhen bound to ligand these proteins initiate a G protein mechanism, which uses cAMP as a second messengercAMP opens Na+ and Ca2+ channels, causing depolarization of the receptor membrane that then triggers an action potentialCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsOlfactory PathwayOlfactory receptor cells synapse with mitral cellsGlomerular mitral cells process odor signalsMitral cells send impulses to:The olfactory cortex The hypothalamus, amygdala, and limbic systemCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsOlfactory Transduction ProcessFigure 15.4Odorant binding proteinOdorant chemicalNa+CytoplasmInactiveActiveNa+ influx causes depolarizationAdenylate cyclaseATPcAMPDepolarization of olfactory receptor cell membrane triggers action potentials in axon of receptorCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsEye and Associated Structures70% of all sensory receptors are in the eyeMost of the eye is protected by a cushion of fat and the bony orbitAccessory structures include eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye musclesCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsEyebrowsCoarse hairs that overlie the supraorbital marginsFunctions include:Shading the eyePreventing perspiration from reaching the eyeOrbicularis muscle – depresses the eyebrowsCorrugator muscles – move the eyebrows mediallyCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsPalpebrae (Eyelids)Figure 15.5bCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsLacrimal ApparatusConsists of the lacrimal gland and associated ductsLacrimal glands secrete tears TearsContain mucus, antibodies, and lysozymeEnter the eye via superolateral excretory ducts Exit the eye medially via the lacrimal punctumDrain into the nasolacrimal ductCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsLacrimal ApparatusFigure 15.6Copyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsStructure of the EyeballA slightly irregular hollow sphere with anterior and posterior polesThe wall is composed of three tunics – fibrous, vascular, and sensoryThe internal cavity is filled with fluids called humorsThe lens separates the internal cavity into anterior and posterior segmentsCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsStructure of the EyeballFigure 15.8aCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsVascular Tunic: Ciliary BodyA thickened ring of tissue surrounding the lensComposed of smooth muscle bundles (ciliary muscles)Anchors the suspensory ligament that holds the lens in placeCopyright © 2004 Pearson Education, Inc., publishing as Benjamin CummingsVascular Tunic: IrisThe colored part of the eyePupil – central opening of the irisRegulates the amount of light entering the eye during: Close vision and bright light – pupils constrictDistant vision and dim light – pupils dilateChanges in emotional state – pupils dilate when the subject matter is appealing or