SPECIAL SENSESSPECIAL SENSES• SMELL, TASTE, AND HEARINGSMELL, TASTE, AND HEARING

The Chemical Senses: The Chemical Senses: Smell And TasteSmell And Taste

• Smell (Smell (olfactionolfaction) and taste () and taste (gustationgustation))

• ChemoreceptorsChemoreceptors respond to chemicals in respond to chemicals in aqueous solutionaqueous solution

Olfactoryepithelium

Olfactory tractOlfactory bulb

Nasalconchae

Route ofinhaled air

Figure 15.20b Olfactory receptors.

Olfactorytract

Olfactorygland

Olfactoryepithelium

Mucus

Mitral cell(output cell)

Olfactory bulb

Cribriform plateof ethmoid bone

Filaments ofolfactory nerveLamina propriaconnective tissue

Olfactory stem cell Olfactory sensoryneuron

DendriteOlfactory cilia

Route of inhaled aircontaining odor molecules

Glomeruli

Olfactory axon

Supporting cell

Olfactory Epithelium and Olfactory Epithelium and the Sense of Smellthe Sense of Smell

• Olfactory epitheliumOlfactory epithelium in roof of nasal cavity in roof of nasal cavity• Contains olfactory sensory neuronsContains olfactory sensory neurons• Olfactory stem cells lie at base of epitheliumOlfactory stem cells lie at base of epithelium

• Olfactory nerve (cranial nerve I)Olfactory nerve (cranial nerve I)

Specificity of Olfactory Specificity of Olfactory ReceptorsReceptors

• Humans can distinguish ~10,000 odorsHumans can distinguish ~10,000 odors

• ~400 "smell" genes active only in nose~400 "smell" genes active only in nose• Each encodes unique receptor proteinEach encodes unique receptor protein

• Protein responds to one or more odorsProtein responds to one or more odors

Physiology of SmellPhysiology of Smell

• Gaseous odorant must dissolve in fluid of Gaseous odorant must dissolve in fluid of olfactory epitheliumolfactory epithelium

• Activation of olfactory sensory neuronsActivation of olfactory sensory neurons• Dissolved odorants bind to receptors in olfactory Dissolved odorants bind to receptors in olfactory

membranesmembranes

Taste Buds and the Sense Taste Buds and the Sense of Tasteof Taste

• Receptor organs are taste buds Receptor organs are taste buds • Most of 10,000 taste buds on tongue papillaeMost of 10,000 taste buds on tongue papillae• Few on soft palate, cheeks, pharynx, epiglottisFew on soft palate, cheeks, pharynx, epiglottis

Figure 15.22a Location and structure of taste buds on the tongue.

Epiglottis

Palatine tonsil

Lingual tonsil

Foliatepapillae

Fungiformpapillae

Taste buds are associatedwith fungiform, foliate, andvallate papillae.

Vallate papilla

Enlarged section of avallate papilla.

Taste bud

Figure 15.22b Location and structure of taste buds on the tongue.

Structure of a Taste BudStructure of a Taste Bud

• Gustatory epithelial cells—taste cellsGustatory epithelial cells—taste cells• Microvilli (gustatory hairs) are receptorsMicrovilli (gustatory hairs) are receptors

Figure 15.22c Location and structure of taste buds on the tongue.

Gustatoryhair

Connective tissue

Taste fibersof cranialnerve

Basalepithelial

cells

Gustatory epithelial

cells

Tastepore

Stratifiedsquamousepitheliumof tongue

Enlarged view of a tastebud (210x).

Basic Taste SensationsBasic Taste Sensations

• There are five basic taste sensationsThere are five basic taste sensations

1.1. SweetSweet—sugars, saccharin, alcohol, some amino acids, —sugars, saccharin, alcohol, some amino acids, some lead saltssome lead salts

2.2. SourSour—hydrogen ions in solution—hydrogen ions in solution

3.3. SaltySalty—metal ions (inorganic salts)—metal ions (inorganic salts)

4.4. BitterBitter—alkaloids such as quinine and nicotine; aspirin—alkaloids such as quinine and nicotine; aspirin

5.5. UmamiUmami—amino acids glutamate and aspartate—amino acids glutamate and aspartate

Basic Taste SensationsBasic Taste Sensations

• Possible sixth tastePossible sixth taste• Growing evidence humans can taste long-chain Growing evidence humans can taste long-chain

fatty acids from lipidsfatty acids from lipids• Perhaps explain liking of fatty foodsPerhaps explain liking of fatty foods

Physiology of TastePhysiology of Taste

• To taste, chemicals mustTo taste, chemicals must• Be dissolved in salivaBe dissolved in saliva• Diffuse into taste poreDiffuse into taste pore• Contact gustatory hairsContact gustatory hairs

Influence of other Influence of other Sensations on TasteSensations on Taste

• Taste is 80% smellTaste is 80% smell

• ThermoreceptorsThermoreceptors, , mechanoreceptorsmechanoreceptors, , nociceptorsnociceptors in mouth also influence tastes in mouth also influence tastes• Temperature and texture enhance or detract Temperature and texture enhance or detract

from tastefrom taste

Homeostatic Imbalances of the Homeostatic Imbalances of the Chemical SensesChemical Senses

• AnosmiasAnosmias (olfactory disorders) (olfactory disorders)• Most result of head injuries and neurological Most result of head injuries and neurological

disorders (Parkinson's disease)disorders (Parkinson's disease)• Uncinate fits Uncinate fits – olfactory hallucinations– olfactory hallucinations

• Olfactory auras prior to epileptic fitsOlfactory auras prior to epileptic fits

The Ear: Hearing and The Ear: Hearing and BalanceBalance

• Three major areas of earThree major areas of ear1.1. External (outer) ear External (outer) ear – hearing only– hearing only

2.2. Middle earMiddle ear (tympanic cavity) – hearing only (tympanic cavity) – hearing only

3.3. Internal (inner) ear Internal (inner) ear – hearing and – hearing and equilibriumequilibrium

• Receptors for hearing and balance respond to Receptors for hearing and balance respond to separate stimuliseparate stimuli

• Are activated independentlyAre activated independently

Figure 15.24a Structure of the ear.

Externalear

Middleear

Internal ear(labyrinth)

Auricle(pinna)

Helix

Lobule

Externalacousticmeatus

Tympanicmembrane

Pharyngotympanic(auditory) tube

The three regions of the ear

External EarExternal Ear

• AuricleAuricle (pinna)Composed of (pinna)Composed of • Helix (rim); Lobule (earlobe)Helix (rim); Lobule (earlobe)• Funnels sound waves into auditory canalFunnels sound waves into auditory canal

• External acoustic meatusExternal acoustic meatus (auditory canal) (auditory canal)• Short, curved tube lined with skin bearing hairs, Short, curved tube lined with skin bearing hairs,

sebaceous glands, and ceruminous glandssebaceous glands, and ceruminous glands• Transmits sound waves to eardrumTransmits sound waves to eardrum

External EarExternal Ear

• Tympanic membraneTympanic membrane (eardrum) (eardrum)• Boundary between external and middle earsBoundary between external and middle ears• Connective tissue membrane that vibrates in Connective tissue membrane that vibrates in

response to soundresponse to sound• Transfers sound energy to bones of middle ear Transfers sound energy to bones of middle ear

Middle Ear Middle Ear

• Mastoid antrumMastoid antrum• Canal for communication with mastoid air cellsCanal for communication with mastoid air cells

• Pharyngotympanic (auditory)Pharyngotympanic (auditory) tubetube——connects middle ear to nasopharynxconnects middle ear to nasopharynx• Equalizes pressure in middle ear cavity with Equalizes pressure in middle ear cavity with

external air pressureexternal air pressure

Oval window(deep to stapes)

Semicircularcanals

Vestibule

Vestibularnerve

Cochlearnerve

Cochlea

Pharyngotympanic(auditory) tube

Entrance to mastoid antrum in the epitympanic recess

Auditoryossicles

Tympanic membrane

Round window

Stapes(stirrup)

Incus(anvil)

Malleus(hammer)

Middle and internal ear

View

Superior

Anterior

Lateral

IncusMalleusEpitympanic

recess

Pharyngotym-panic tube

Tensortympanimuscle

Tympanicmembrane(medial view)

Stapes Stapediusmuscle

Temporalbone

Facial nerve

Vestibular nerve

Superior vestibularganglionInferior vestibularganglionCochlear nerveMaculaeSpiral organ

Cochlear ductin cochlea

Round windowStapes inoval window

Saccule investibule

Utricle investibule

Cristae ampullaresin the membranousampullae

LateralPosteriorAnterior

Semicircular ductsin semicircularcanals

VestibuleVestibule

• Contains two membranous sacsContains two membranous sacs1.1. SacculeSaccule is continuous with cochlear duct is continuous with cochlear duct

2.2. UtricleUtricle is continuous with semicircular canals is continuous with semicircular canals

• These sacsThese sacs• House equilibrium receptor regions (maculae)House equilibrium receptor regions (maculae)• Respond to gravity and changes in position of headRespond to gravity and changes in position of head

Semicircular CanalsSemicircular Canals

• Three canals (anterior, lateral, and posterior) Three canals (anterior, lateral, and posterior) that each define ⅔ circlethat each define ⅔ circle• Lie in three planes of spaceLie in three planes of space

Temporalbone

Facial nerve

Vestibular nerve

Superior vestibularganglionInferior vestibularganglionCochlear nerveMaculaeSpiral organ

Cochlear ductin cochlea

Round windowStapes inoval window

Saccule investibule

Utricle investibule

Cristae ampullaresin the membranousampullae

LateralPosteriorAnterior

Semicircular ductsin semicircularcanals

The CochleaThe Cochlea

• A spiral, conical, bony chamberA spiral, conical, bony chamber• Size of split peaSize of split pea

Vestibular membrane

Tectorial membrane

Cochlear duct(scala media;containsendolymph)

Striavascularis

Spiral organ

Basilarmembrane

Scala vestibuli(containsperilymph)

Scala tympani(containsperilymph)

Osseous spiral lamina

Spiralganglion

Tectorial membrane

Hairs (stereocilia)

Outer hair cells

Supporting cells

Inner hair cell

Afferent nervefibers

Fibers ofcochlearnerve

Basilarmembrane

Innerhaircell

Outerhaircell