Special Senses: Special Senses: Hearing, Taste, Hearing, Taste,

SmellSmellPeripheral Nervous SystemPeripheral Nervous System

Chapter 15Chapter 15

The SensesThe Senses General senses of touch (tactile)

Temperature - thermoreceptors (heat) Pressure - mechanoreceptors (movement) Pain - mechanoreceptors

Special senses Smell - chemoreceptors (chemicals) Taste - chemoreceptors Sight - photoreceptors (light) Hearing - mechanoreceptors Equilibrium - (balance) mechanoreceptors

The Ear: Hearing and The Ear: Hearing and BalanceBalance

Two functions: Hearing and Two functions: Hearing and BalanceBalance Hearing: Sound vibrationsHearing: Sound vibrations Equilibrium: Gross movementsEquilibrium: Gross movements

MechanoreceptorsMechanoreceptors: respond to : respond to physical forcesphysical forces

Both respond to different stimuli and Both respond to different stimuli and activated separatelyactivated separately

Anatomy of EarAnatomy of Ear

HEARING ONLY

HEARING &

BALANCE

Anatomy of EarAnatomy of Ear

Divided into 3 regions: Divided into 3 regions: External, Middle, InternalExternal, Middle, Internal

External EarExternal Ear Auricle (pinna) and Auditory Auricle (pinna) and Auditory

CanalCanal Ceruminous Glands in canal Ceruminous Glands in canal

secrete earwaxsecrete earwax Tympanic membrane - eardrumTympanic membrane - eardrum

Why do we need earwax???

Earwax protects delicate lining of meatus (auditory canal) and helps prevent microorganisms from entering the ear

Anatomy of EarAnatomy of Ear

Middle EarMiddle Ear Tympanic Cavity – air filled, Tympanic Cavity – air filled,

mucosa-linedmucosa-lined Eustachian Tube – connects to Eustachian Tube – connects to

throatthroat Auditory Auditory ossiclesossicles (tiny bones) (tiny bones)

– hammer, anvil, stirrup– hammer, anvil, stirrup Eustacian tubePressure build upSwallowingyawning“VALSALVA”

THROAT

Otitis mediaOtitis media

Middle ear Middle ear inflammationinflammation

Common with sore Common with sore throat in childrenthroat in children

Enlarge, inflamed Enlarge, inflamed eardrumeardrum

Pus, fluid build up Pus, fluid build up requires incision requires incision and tubes to relieve and tubes to relieve pressure and drainpressure and drain

http://www.petearclinic.com/images_video.htm

http://apps.uwhealth.org/health/hie/2/19596.htm

Anatomy of EarAnatomy of Ear INNER EARINNER EAR

This is a cavityThis is a cavity Bony labyrinth – Bony labyrinth –

bony chamber bony chamber divided into 3 divided into 3 regionsregions CochleaCochlea VestibuleVestibule Semicircular CanalsSemicircular Canals

Two fluids:Two fluids: EndolymphEndolymph PerilymphPerilymph

Labyrinth: an intricate, sometimes confusing, arrangement or pattern

Figure 8.15

HearingHearing

Within Cochlear duct, membranous labyrinth is Spiral Organ of Corti – hearing receptors or “hair cells”

Sound waves > eardrum > ossicles > oval window > set fluid in motion > vibrations stimulate “hair

cells” > cochlear nerve transmits impulse to midbrain > auditory cortex

of temporal lobe

How the ear works…How the ear works…

http://www.youtube.com/watch?v=dCyz8-eAs1I

Chemical Senses: Taste and Chemical Senses: Taste and SmellSmell

ChemoreceptorChemoreceptor – respond to – respond to chemicals in solutionchemicals in solution OLFACTORY OLFACTORY = smell= smell GUSTATORYGUSTATORY = taste = taste

Five types of receptors for tasteFive types of receptors for taste Olfactory receptors much more Olfactory receptors much more

sensitivesensitive Complement each other, respond to Complement each other, respond to

same stimulisame stimuli

Smell not as good as animals; however, some people are wine tasters, perfumers

If you smell a particular odor all day, you won’t recognize its presence, you become accustomed, ex. garbage men

Old people lose sense of smell- lots of perfume

Humans can distinguish 10,000 or so chemicals

What we really smell is pain: ex. chili, ammonia, menthol (cold)

Specific chemicals cause specific patterns of neurons to fire

Figure 15.21a

Olfactory tract

Olfactory bulb

(a)

Nasalconchae

Route ofinhaled air

Olfactoryepithelium

Olfactory Receptors: Olfactory Receptors: SmellSmell

1000’s of olfactory receptors roof of 1000’s of olfactory receptors roof of nasal cavitynasal cavity

Sniffing intensifies sense of smellSniffing intensifies sense of smell

Olfactory receptor cells have olfactory Olfactory receptor cells have olfactory hairs – long cilia – in mucus layerhairs – long cilia – in mucus layer

Chemicals in mucus layer stimulate hairs Chemicals in mucus layer stimulate hairs -> filaments -> nerve-> filaments -> nerve

Olfactory impressions long lasting – Olfactory impressions long lasting – memories, adaptivememories, adaptive

Figure 8.17

Figure 15.21a

Mitral cell (output cell)

Olfactorygland

Olfactorytract

Olfactoryepithelium

Filaments of olfactory nerve

Cribriform plate of ethmoid bone

Lamina propria connective tissue

Basal cell

Supporting cell

Dendrite

Olfactory cilia

Olfactory bulbGlomeruli

Axon

Olfactory receptor cell

Mucus

Route of inhaled aircontaining odor molecules(b)

Pathway of smellPathway of smell

http://www.youtube.com/watch?v=dIDBG-UPRUI

Nostril > nasal cavity > olfactory receptors (sensory neurons) in membrane (top of nasal cavity) > through ethmoid (bone) > olfactory neurons in olfactory bulb > brain

Taste Buds and TasteTaste Buds and Taste Most pleasurable Most pleasurable

sensesense Approx. 10,000 taste Approx. 10,000 taste

buds, most on tonguebuds, most on tongue Papillae – Papillae –

projections, taste projections, taste buds found on sidesbuds found on sides Circumvallate papillae Circumvallate papillae

– sides of tongue– sides of tongue Fungiform papillae – Fungiform papillae –

top, more numeroustop, more numerous

Figure 8.18

Taste BudsTaste BudsTaste BudsTaste Buds

Circumvallate Papilla

Filiformpapilla

Fungiformpapilla

Connective tissue Tongue epithelium

Taste BudsTaste Buds

Figure 8.18

Gustatory cells – Gustatory cells – respond to respond to chemicalschemicals

Gustatory hairs – Gustatory hairs – microvilli, protrude microvilli, protrude through taste porethrough taste pore

Chewed food mixes with saliva > solution slides down to sides of papillae > enters taste pore > stimulate gustatory hairs > stimulate gustatory receptor cells > impulse travels by nerves to brain

Five Taste SensationsFive Taste Sensations SWEETSWEET – sugars, – sugars,

saccharine, some a.a., saccharine, some a.a., lead saltslead salts

SOURSOUR -- acids -- acids BITTERBITTER – alkaloids – alkaloids SALTYSALTY – metal ions in – metal ions in

solutionsolution UMAMIUMAMI– a.a. glutamate, – a.a. glutamate,

“beef taste” and MSG“beef taste” and MSG Only slight differences in Only slight differences in

receptor location. receptor location. Most buds respond to 2+ Most buds respond to 2+

stimulistimuli

http://pactlab-dev.spcomm.uiuc.edu/classes/08SP/280blogs/first_weblog3/2008/02/digitizing-your-taste-buds.html

TasteTaste

Homeostatic roleHomeostatic role Tastes for salt or sugar – minerals or Tastes for salt or sugar – minerals or

carbscarbs Sour – Oranges, lemons – Vitamin CSour – Oranges, lemons – Vitamin C Umami – protein intakeUmami – protein intake Bitter – most poisons and spoiled food Bitter – most poisons and spoiled food

bitter, protectivebitter, protective

Factors of TasteFactors of Taste

Temperature, textureTemperature, texture Spicy food excites pain receptors in Spicy food excites pain receptors in

mouthmouth Taste and Smell ComplementaryTaste and Smell Complementary

Eating when you have coldEating when you have cold

Loss of Chemical SensesLoss of Chemical Senses

Beginning in 40’s ability to taste and Beginning in 40’s ability to taste and smell diminishessmell diminishes Decrease in # of receptorsDecrease in # of receptors About 50% over 80 cannot smellAbout 50% over 80 cannot smell Sense of taste is poorSense of taste is poor

The EndThe End