11

Chapter 16Chapter 16The Special SensesThe Special Senses

• Smell, taste, vision, hearing and Smell, taste, vision, hearing and equilibriumequilibrium

• Housed in complex sensory organs Housed in complex sensory organs

• Ophthalmology is science of the Ophthalmology is science of the eyeeye

• Otolaryngology is science of the Otolaryngology is science of the earear

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Chemical SensesChemical Senses

• Interaction of molecules with receptor Interaction of molecules with receptor cellscells

• Olfaction (smell) and gustation (taste)Olfaction (smell) and gustation (taste)

• Both project to cerebral cortex & Both project to cerebral cortex & limbic systemlimbic system– evokes strong emotional reactionsevokes strong emotional reactions

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Olfactory EpitheliumOlfactory Epithelium

• 1 square inch of 1 square inch of membrane holding membrane holding 10-100 million 10-100 million receptorsreceptors

• Covers superior Covers superior nasal cavity and nasal cavity and cribriform platecribriform plate

• 3 types of receptor 3 types of receptor cellscells

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Olfaction: Sense of SmellOlfaction: Sense of Smell

• Odorants bind to Odorants bind to receptorsreceptors

• Na+ channels Na+ channels openopen

• Depolarization Depolarization occursoccurs

• Nerve impulse is Nerve impulse is triggeredtriggered

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Adaptation & Odor Adaptation & Odor ThresholdsThresholds

• Adaptation = decreasing sensitivityAdaptation = decreasing sensitivity

• Olfactory adaptation is rapidOlfactory adaptation is rapid– 50% in 1 second50% in 1 second– complete in 1 minutecomplete in 1 minute

• Low thresholdLow threshold– only a few molecules need to be presentonly a few molecules need to be present– methyl mercaptan added to natural gas methyl mercaptan added to natural gas

as warningas warning

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Gustatory Sensation: Gustatory Sensation: TasteTaste

• Taste requires Taste requires dissolving of dissolving of substancessubstances

• Four classes of Four classes of stimuli--sour, bitter, stimuli--sour, bitter, sweet, and saltysweet, and salty

• 10,000 taste buds 10,000 taste buds found on tongue, soft found on tongue, soft palate & larynxpalate & larynx

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Anatomy of Taste BudsAnatomy of Taste Buds

• An oval body An oval body consisting of 50 consisting of 50 receptor cells receptor cells surrounded by surrounded by supporting cellssupporting cells

• A single gustatory A single gustatory hair projects upward hair projects upward through the taste through the taste porepore

• Basal cells develop Basal cells develop into new receptor into new receptor cells every 10 days.cells every 10 days.

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Physiology of TastePhysiology of Taste

• Complete adaptation in 1 to 5 minutesComplete adaptation in 1 to 5 minutes

• Thresholds for tastes vary among the Thresholds for tastes vary among the 4 primary tastes4 primary tastes– most sensitive to bitter (poisons)most sensitive to bitter (poisons)– least sensitive to salty and sweetleast sensitive to salty and sweet

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Accessory Structures of Accessory Structures of EyeEye

• Eyelids or Eyelids or palpebraepalpebrae– protect & lubricateprotect & lubricate

• Tarsal glandsTarsal glands– oily secretions keep oily secretions keep

lids from sticking lids from sticking togethertogether

• ConjunctivaConjunctiva– stops at corneal stops at corneal

edgeedge– dilated BV--dilated BV--

bloodshot bloodshot

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Eyelashes & EyebrowsEyelashes & Eyebrows

• Eyelashes & eyebrows help protect from foreign Eyelashes & eyebrows help protect from foreign objects, perspiration & sunlightobjects, perspiration & sunlight

• Sebaceous glands are found at base of eyelashes Sebaceous glands are found at base of eyelashes (sty) (sty)

• Palpebral fissure is gap between the eyelidsPalpebral fissure is gap between the eyelids

Eyeball = 1 inch diameter

5/6 of Eyeball inside orbit & protected

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Lacrimal ApparatusLacrimal Apparatus

• About 1 ml of tears produced per day. Spread over eye by About 1 ml of tears produced per day. Spread over eye by blinking. Contains bactericidal enzyme called lysozyme.blinking. Contains bactericidal enzyme called lysozyme.

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Extraocular MusclesExtraocular Muscles

• Six muscles that Six muscles that insert on the insert on the exterior surface of exterior surface of the eyeballthe eyeball

• ..

• 4 rectus muscles -- 4 rectus muscles -- superior, inferior, superior, inferior, lateral and mediallateral and medial

• 2 oblique muscles -- 2 oblique muscles -- inferior and superiorinferior and superior

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Tunics (Layers) of EyeballTunics (Layers) of Eyeball

• Fibrous TunicFibrous Tunic(outer layer)(outer layer)

• Vascular Tunic Vascular Tunic

(middle layer)(middle layer)

• Nervous TunicNervous Tunic(inner layer)(inner layer)

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• Transparent Transparent

• Helps focus light(refraction)Helps focus light(refraction)– astigmatismastigmatism

• TransplantsTransplants– common & successfulcommon & successful– no blood vessels so no antibodies to cause rejectionno blood vessels so no antibodies to cause rejection

Fibrous Tunic -- Description of Fibrous Tunic -- Description of CorneaCornea

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Fibrous Tunic -- Description of Fibrous Tunic -- Description of ScleraSclera

• ““White” of the eyeWhite” of the eye

• Dense irregular Dense irregular connective tissue connective tissue layer -- collagen & layer -- collagen & fibroblastsfibroblasts

• Provides shape & Provides shape & supportsupport

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Vascular Tunic -- Choroid & Ciliary Vascular Tunic -- Choroid & Ciliary BodyBody

• ChoroidChoroid– pigmented epithilial cells pigmented epithilial cells

(melanocytes) & blood (melanocytes) & blood vesselsvessels

– provides nutrients to provides nutrients to retinaretina

– black pigment in black pigment in melanocytes absorb melanocytes absorb scattered light scattered light

• Ciliary bodyCiliary body– ciliary processes ciliary processes

• folds on ciliary bodyfolds on ciliary body

• secrete aqueous humorsecrete aqueous humor

– ciliary muscleciliary muscle• smooth muscle that alters smooth muscle that alters

shape of lensshape of lens

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Vascular Tunic -- Iris & Vascular Tunic -- Iris & PupilPupil

• Colored portion of eyeColored portion of eye

• Shape of flat donut Shape of flat donut suspended between suspended between cornea & lenscornea & lens

• Hole in center is pupilHole in center is pupil

• Function is to regulate Function is to regulate amount of light amount of light entering eyeentering eye

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Vascular Tunic -- Description of Vascular Tunic -- Description of lenslens

• AvascularAvascular

• Crystallin proteins Crystallin proteins arranged like arranged like layers in onionlayers in onion

• Clear capsule & Clear capsule & perfectly perfectly transparenttransparent

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Nervous Tunic -- RetinaNervous Tunic -- Retina• Posterior 3/4 of Posterior 3/4 of

eyeballeyeball

• Optic discOptic disc– optic nerve exiting optic nerve exiting

back of eyeballback of eyeball

• Central retina BVCentral retina BV– fan out to supply fan out to supply

nourishment to retinanourishment to retina– visible for inspectionvisible for inspection

• hypertension & hypertension & diabetesdiabetes

• Detached retinaDetached retina– trauma (boxing)trauma (boxing)

• fluid between layersfluid between layers

• distortion or blindnessdistortion or blindness

View with Ophthalmoscope

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Rods & Cones--Rods & Cones--PhotoreceptorsPhotoreceptors• Rods----rod shapedRods----rod shaped

– shades of gray in dim shades of gray in dim lightlight

– 120 million rod cells120 million rod cells– discriminates shapes & discriminates shapes &

movementsmovements– distributed along distributed along

periphery periphery

• Cones----cone shapedCones----cone shaped– sharp, color visionsharp, color vision– 6 million6 million– fovea of macula luteafovea of macula lutea

• densely packed regiondensely packed region

• at exact visual axis of eyeat exact visual axis of eye

• 2nd cells do not cover cones2nd cells do not cover cones

• sharpest resolution or acuitysharpest resolution or acuity

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Pathway of Nerve Signal in Pathway of Nerve Signal in RetinaRetina

• Light penetrates retinaLight penetrates retina

• Rods & cones Rods & cones transduce light into transduce light into action potentialsaction potentials

• Rods & cones excite Rods & cones excite bipolar cellsbipolar cells

• Bipolars excite Bipolars excite ganglion cellsganglion cells

• Axons of ganglion cells Axons of ganglion cells form optic nerve form optic nerve leaving the eyeball leaving the eyeball (blind spot)(blind spot)

• To thalamus & then the To thalamus & then the primary visual cortexprimary visual cortex

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Aqueous HumorAqueous Humor• Continuously produced Continuously produced

by ciliary bodyby ciliary body

• Flows from posterior chamberFlows from posterior chamberinto anterior through the pupilinto anterior through the pupil

• GlaucomaGlaucoma– increased intraocular pressure that could produce blindnessincreased intraocular pressure that could produce blindness– problem with drainage of aqueous humorproblem with drainage of aqueous humor

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Major Processes of Image Major Processes of Image FormationFormation

• Refraction of lightRefraction of light– by cornea & lens by cornea & lens – light rays must fall upon the retinalight rays must fall upon the retina

• Accommodation of the lensAccommodation of the lens– changing shape of lens so that light is changing shape of lens so that light is

focusedfocused

• Constriction of the pupilConstriction of the pupil– less light enters the eyeless light enters the eye

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Definition of RefractionDefinition of Refraction

• Bending of light as it passes from one substance Bending of light as it passes from one substance (air) into a 2nd substance with a different (air) into a 2nd substance with a different density(cornea)density(cornea)

• In the eye, light is refracted by the anterior & In the eye, light is refracted by the anterior & posterior surfaces of the cornea and the lensposterior surfaces of the cornea and the lens

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Refraction by the Cornea Refraction by the Cornea & Lens& Lens

• Image focused on retina is Image focused on retina is inverted & reversed from left inverted & reversed from left to rightto right

• Brain learns to work with that Brain learns to work with that informationinformation

• 75% of Refraction is done by75% of Refraction is done by cornea -- rest is done by the cornea -- rest is done by the lenslens

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Near Point of Vision and Near Point of Vision and PresbyopiaPresbyopia

• Near point is the closest distance from the Near point is the closest distance from the eye an object can be & still be in clear eye an object can be & still be in clear focusfocus– 4 inches in a young adult4 inches in a young adult– 8 inches in a 40 year old8 inches in a 40 year old

• lens has become less elasticlens has become less elastic

– 31 inches in a 60 to 80 year old31 inches in a 60 to 80 year old

• Reading glasses may be needed by age 40Reading glasses may be needed by age 40– presbyopiapresbyopia– glasses replace refraction previously provided glasses replace refraction previously provided

by increased curvature of the relaxed, by increased curvature of the relaxed, youthful lensyouthful lens

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Correction for Refraction Correction for Refraction ProblemsProblems

• Emmetropic eye (normal)Emmetropic eye (normal)– can refract light from 20 ft awaycan refract light from 20 ft away

• Myopia (nearsighted)Myopia (nearsighted)– eyeball is too long from front to backeyeball is too long from front to back– glasses concave glasses concave

• Hypermetropic (farsighted)Hypermetropic (farsighted)– eyeball is too shorteyeball is too short– glasses convex (coke-bottle)glasses convex (coke-bottle)

• AstigmatismAstigmatism– corneal surface wavycorneal surface wavy– parts of image out of focusparts of image out of focus

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Constriction of the PupilConstriction of the Pupil

• Constrictor pupillae muscle contractsConstrictor pupillae muscle contracts

• Prevents light rays from entering the Prevents light rays from entering the eye through the edge of the lenseye through the edge of the lens

• Sharpens vision by preventing blurry Sharpens vision by preventing blurry edgesedges

• Protects retina very excessively Protects retina very excessively bright lightbright light

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Convergence of the EyesConvergence of the Eyes

• Binocular vision in humans has both Binocular vision in humans has both eyes looking at the same objecteyes looking at the same object

• As you look at an object close to your As you look at an object close to your face, both eyeballs must turn inward.face, both eyeballs must turn inward.– convergenceconvergence

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PhotoreceptorsPhotoreceptors• Photopigment is integral Photopigment is integral

membrane protein of outer membrane protein of outer segment membrane segment membrane – photopigment membrane folded photopigment membrane folded

into “discs” & replaced at a very into “discs” & replaced at a very rapid raterapid rate

• Photopigments = opsin Photopigments = opsin (protein) + retinal (derivative (protein) + retinal (derivative of vitamin A)of vitamin A)– rods contain rhodopsinrods contain rhodopsin– cone photopigments contain 3 cone photopigments contain 3

different opsin proteins different opsin proteins permitting the absorption of 3 permitting the absorption of 3 different wavelengths (colors) of different wavelengths (colors) of lightlight

3131

Color Blindness & Night Color Blindness & Night BlindnessBlindness

• Color blindnessColor blindness– inability to distinguish between certain inability to distinguish between certain

colorscolors– absence of certain cone photopigmentsabsence of certain cone photopigments– red-green color blind person can not tell red-green color blind person can not tell

red from greenred from green

• Night blindness (nyctalopia)Night blindness (nyctalopia)– difficulty seeing in low lightdifficulty seeing in low light– inability to make normal amount of inability to make normal amount of

rhodopsinrhodopsin– possibly due to deficiency of vitamin Apossibly due to deficiency of vitamin A

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Light and Dark AdaptationLight and Dark Adaptation

• Light adaptationLight adaptation– adjustments when emerge from the dark into the adjustments when emerge from the dark into the

lightlight

• Dark adaptationDark adaptation– adjustments when enter the dark from a bright adjustments when enter the dark from a bright

situationsituation– light sensitivity increases as photopigments light sensitivity increases as photopigments

regenerateregenerate•during first 8 minutes of dark adaptation, only cone during first 8 minutes of dark adaptation, only cone

pigments are regenerated, so threshold burst of light is pigments are regenerated, so threshold burst of light is seen as colorseen as color

•after sufficient time, sensitivity will increase so that a after sufficient time, sensitivity will increase so that a flash of a single photon of light will be seen as gray-whiteflash of a single photon of light will be seen as gray-white

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Brain Pathways of VisionBrain Pathways of Visionsynapse in thalamus & visual cortex

3434

Processing of Image Data in Processing of Image Data in the Brainthe Brain• Visual information in optic nerve Visual information in optic nerve

travels totravels to– occipital lobe for visionoccipital lobe for vision– midbrain for controlling pupil size & midbrain for controlling pupil size &

coordination of head and eye movementscoordination of head and eye movements– hypothalamus to establish sleep patterns hypothalamus to establish sleep patterns

based upon circadian rhythms of light based upon circadian rhythms of light and darknessand darkness

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Visual fieldsVisual fields• Left occipital lobe Left occipital lobe

receives visual receives visual images from right images from right side of an object side of an object through impulses through impulses from nasal 1/2 of the from nasal 1/2 of the right eye and right eye and temporal 1/2 of the temporal 1/2 of the left eyeleft eye

• Left occipital lobe Left occipital lobe sees right 1/2 of the sees right 1/2 of the worldworld

• Fibers from nasal 1/2 Fibers from nasal 1/2 of each retina cross of each retina cross in optic chiasmin optic chiasm

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Anatomy of the Ear RegionAnatomy of the Ear Region

3737

External EarExternal Ear• Function = collect soundsFunction = collect sounds• StructuresStructures

– auricle or pinnaauricle or pinna•elastic cartilage covered with skinelastic cartilage covered with skin

– external auditory canal external auditory canal •curved 1” tube of cartilage & bone leading into curved 1” tube of cartilage & bone leading into

temporal bonetemporal bone•ceruminous glands produce cerumen = ear waxceruminous glands produce cerumen = ear wax

– tympanic membrane or eardrumtympanic membrane or eardrum•epidermis, collagen & elastic fibers, simple cuboidal epidermis, collagen & elastic fibers, simple cuboidal

epith.epith.

• Perforated eardrum (hole is present) Perforated eardrum (hole is present) – at time of injury (pain, ringing, hearing loss, at time of injury (pain, ringing, hearing loss,

dizziness)dizziness)– caused by explosion, scuba diving, or ear infectioncaused by explosion, scuba diving, or ear infection

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Middle Ear CavityMiddle Ear Cavity

3939

Middle Ear CavityMiddle Ear Cavity• Air filled cavity in the temporal bone Air filled cavity in the temporal bone

• Separated from external ear by Separated from external ear by eardrum and from internal ear by eardrum and from internal ear by oval & round windowoval & round window

• 3 ear ossicles connected by synovial joints3 ear ossicles connected by synovial joints– malleus attached to eardrum, incus & stapes malleus attached to eardrum, incus & stapes

attached by foot plate to membrane of oval attached by foot plate to membrane of oval windowwindow

– stapedius and tensor tympani muscles attach to stapedius and tensor tympani muscles attach to ossiclesossicles

• Auditory tube leads to nasopharynxAuditory tube leads to nasopharynx– helps to equalize pressure on both sides of helps to equalize pressure on both sides of

eardrumeardrum

• Connection to mastoid bone =mastoiditisConnection to mastoid bone =mastoiditis

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Inner Ear---Bony LabyrinthInner Ear---Bony Labyrinth

ampulla

Vestibule

• Bony labyrinth = set of tubelike cavities in Bony labyrinth = set of tubelike cavities in temporal bonetemporal bone– semicircular canals, vestibule & cochlea lined with semicircular canals, vestibule & cochlea lined with

periosteum & filled with perilymphperiosteum & filled with perilymph– surrounds & protects Membranous Labyrinthsurrounds & protects Membranous Labyrinth

canals

4141

Inner Ear---Membranous Inner Ear---Membranous LabyrinthLabyrinth

• Membranous labyrinth = set of membranous Membranous labyrinth = set of membranous tubes containing sensory receptors for hearing tubes containing sensory receptors for hearing & balance and filled with endolymph& balance and filled with endolymph– utricle, saccule, ampulla, 3 semicircular ducts & utricle, saccule, ampulla, 3 semicircular ducts &

cochleacochlea

4242

Anatomy of the Organ of Anatomy of the Organ of CortiCorti

• 16,000 hair cells have 30-100 stereocilia(microvilli )16,000 hair cells have 30-100 stereocilia(microvilli )

• Microvilli make contact with tectorial membrane Microvilli make contact with tectorial membrane (gelatinous membrane that overlaps the spiral organ of (gelatinous membrane that overlaps the spiral organ of Corti)Corti)

• Basal sides of inner hair cells synapse with 1st order Basal sides of inner hair cells synapse with 1st order sensory neurons whose cell body is in spiral ganglionsensory neurons whose cell body is in spiral ganglion

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Sound WavesSound Waves• Vibrating object causes compression of Vibrating object causes compression of

air around it = sound wavesair around it = sound waves– audible range is 20 to 20,000 Hzaudible range is 20 to 20,000 Hz– hear best within 500 to 5000 cycles/sec or hear best within 500 to 5000 cycles/sec or

HzHz– speech is 100 to 3000 Hzspeech is 100 to 3000 Hz

• Frequency of a sound vibration is pitchFrequency of a sound vibration is pitch– higher frequency is higher pitchhigher frequency is higher pitch

• Greater intensity (size) of vibration, the Greater intensity (size) of vibration, the louder the sound measured in decibels louder the sound measured in decibels (dB)(dB)– Conversation is 60 dB; pain above 140dBConversation is 60 dB; pain above 140dB– OSA requires ear protection above 90dBOSA requires ear protection above 90dB

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DeafnessDeafness

• Nerve deafnessNerve deafness– damage to hair cells from antibiotics, high damage to hair cells from antibiotics, high

pitched sounds, anticancer drugspitched sounds, anticancer drugs•the louder the sound the quicker the hearing the louder the sound the quicker the hearing

lossloss

– fail to notice until difficulty with speechfail to notice until difficulty with speech

• Conduction deafnessConduction deafness– perforated eardrumperforated eardrum– otosclerosisotosclerosis

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Physiology of HearingPhysiology of Hearing• Auricle collects sound wavesAuricle collects sound waves

• Eardrum vibratesEardrum vibrates– slow vibration in response to low-pitched soundsslow vibration in response to low-pitched sounds– rapid vibration in response to high-pitched soundsrapid vibration in response to high-pitched sounds

• Ossicles vibrate since malleus attached to eardrumOssicles vibrate since malleus attached to eardrum

• Stapes pushes on oval window producing fluid Stapes pushes on oval window producing fluid pressure waves in scala vestibuli & tympanipressure waves in scala vestibuli & tympani– oval window vibration 20X more vigorous than eardrumoval window vibration 20X more vigorous than eardrum

• Pressure fluctuations inside cochlear duct move Pressure fluctuations inside cochlear duct move the hair cells against the tectorial membranethe hair cells against the tectorial membrane

• Microvilli are bent producing receptor potentialsMicrovilli are bent producing receptor potentials

4646

Overview of Physiology of Overview of Physiology of HearingHearing

4747

Cochlear ImplantsCochlear Implants

• If deafness is due to destruction of hair If deafness is due to destruction of hair cellscells

• Microphone, microprocessor & Microphone, microprocessor & electrodes translate sounds into electric electrodes translate sounds into electric stimulation of the vestibulocochlear stimulation of the vestibulocochlear nervenerve– artificially induced nerve signals follow artificially induced nerve signals follow

normal pathways to brainnormal pathways to brain

• Provides only a crude representation of Provides only a crude representation of soundssounds

4848

Physiology of Equilibrium Physiology of Equilibrium (Balance)(Balance)

• Static equilibriumStatic equilibrium– maintain the position of the body (head) maintain the position of the body (head)

relative to the force of gravityrelative to the force of gravity

• Dynamic equilibriumDynamic equilibrium– maintain body position (head) during maintain body position (head) during

sudden movement of any type--rotation, sudden movement of any type--rotation, deceleration or accelerationdeceleration or acceleration

4949

Detection of Position of Detection of Position of HeadHead

• Movement of stereocilia or kinocilium results in Movement of stereocilia or kinocilium results in the release of neurotransmitter onto the the release of neurotransmitter onto the vestibular branches of the vestibulocochler nervevestibular branches of the vestibulocochler nerve

5050

Detection of Rotational Detection of Rotational MovementMovement

• When head moves, the attached semicircular When head moves, the attached semicircular ducts and hair cells move with itducts and hair cells move with it

• Nerve signals to the brain are generated Nerve signals to the brain are generated indicating which direction the head has been indicating which direction the head has been rotatedrotated