Biol 219Lect 19Fall2016 Dr Scott

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SpecialSenses

Olfaction,Gustation,Hearing,Equilibrium

OlfactionviaCNI

• Linkbetween smell,memory, andemotion• Olfactorysensoryneurons

• Olfactoryepitheliuminnasalcavity

• Odorantsbindtoodorant receptors,Gprotein–linkedmembrane receptors

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Figure10.13aTheOlfactorySystem

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Olfactory PathwaysThe olfactory epithelium lies high within the nasal cavity, and its olfactory neuronsproject to the olfactory bulb. Sensory inputat the receptors is carried through theolfactory cortex to the cerebral cortex and the limbic system.

Cerebral cortex

Olfactory bulb

Cranial Nerve I

Olfactoryneuronsin olfactoryepithelium

Olfactory tract Olfactory cortex

Limbicsystem

Figure10.13bTheOlfactorySystem

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The olfactory neurons synapse with secondarysensory neurons in the olfactory bulb.

Olfactorybulb

Secondary sensory neurons

Olfactory sensory neurons

Bone

Olfactoryepithelium

Multiple pr imary neurons in the epithelium synapse on onesecondary neuron in the olfactorybulb. This pattern is an example of what pr inciple?

FIGURE QUESTION

Biol 219Lect 19Fall2016 Dr Scott

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Olfactory neurons in the olfactory epithelium live only abouttwo months. They are replaced by new neurons whose axonsmust find their way to the olfactory bulb.

Olfactory neuronaxons (cranial nerve I)

carry information toolfactory bulb.

Lamina propria

Basal cell layer includesstem cells that replace

olfactory neurons.

Olfactorysensory neuron

Supporting cell

Olfactory cilia(dendrites) containodorant receptors.

Mucous layer:Odorant molecules must

dissolve in this layer .

Capillary

Olfactory (Bowman’s) gland

Developingolfactory neuron

Gustation

• Closely linked toolfaction• Taste isacombinationoffivebasicsensations:sweet, sour,salty, bitter,umami.

• Additional tastesensationsmaybe linked toTRPpathways, same asthermoreceptors andnocireceptors:minty, hotspicy

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Gustation- viaCNVII,IX,X

• Taste receptorcellsarenon-neuralepithelium.• Each tastecell issensitive toonlyone taste.• Taste transduction

• Gustducin

• Humansandanimalsmaydevelop specifichunger,suchassaltappetite.

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Figure10.14aTaste

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Taste Buds. Each taste bud is composed of taste cellsjoined near the apical surface with tight junctions.

Taste buds are located on the dorsal surfaceof the tongue.

Taste pore

Taste ligands create Ca2+ signals that release serotonin or ATP.

Sweet Umami Bitter Sour

Tight junction

Type I support cellsmay sense salt when

Na + enters throughchannels.

Salt?

(Based onTomchik et al., JNeurosci 27(40):10840–10848,2007.)

Presynapticcell (III)

ATP

Receptor cells(type II)

Serotonin

Primary sensoryneurons

Light micrograph of a taste bud

Biol 219Lect 19Fall2016 Dr Scott

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TheEar:HearingCNVIII

• Perceptionofenergy carried bysoundwaves• Frequency istranslated intopitch• Loudnessisaninterpretation ofintensity,afunctionofwaveamplitude

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The Ear

EXTERNAL EAR MIDDLE EAR INNER EAR

The pinnadirects sound

waves into the ear. Malleus

Incus

Stapes

Semicircularcanals

Ovalwindow Nerves

The oval window and the round window separate the fluid-filled inner ear from the air-filled middle ear.

Ear canal

Tympanicmembrane

Roundwindow

Eustachiantube

Topharynx

Vestibularapparatus

Cochlea

Figure10.16aSoundwaves

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Sound waves alternate peaks of compressed air and valleys where the air is less compressed.

Wavelength

Tuning fork

Figure10.16bSoundwaves

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Sound waves are distinguished by their frequency, measuredin hertz (Hz), and amplitude, measured in decibels (dB).

1. What are the frequencies of the sound waves in graphs (1) and (2)in Hz (waves/second)?

2. Which set of sound waves would be interpreted as having lower pitch?

1 Wavelength

Amplitude(dB)

Intensity(dB)

0 0.25Time (sec)

(1)

(2)

Amplitude(dB)

Intensity(dB)

0 0.25Time (sec)

FIGURE QUESTIONS

Biol 219Lect 19Fall2016 Dr Scott

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SoundTransduction

• Soundwaves tomechanical vibrationswhenstriking the tympanicmembrane (eardrum)

• Three middlebonesvibrate andtransfer tomembrane inovalwindow

• Vibrationsgenerate fluidwaves inthecochlea• Haircellsbend inthecochleaandionchannelsopen

• Actionpotential travel tothebrain

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Sl id e2

Sound wave sstrike the tympan icmembrane and be come vib rations.

Ear canal Malle us

Incus

Stape sOval

window

Coch le arne rve

Ve stibu larduct(pe ri lymph)

Coch le arduct(e ndo lymph)

Tympan ic duct(pe ri lymph)

Roundwindow

Tympan icmembrane

Movemento f soundwave s

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Sl id e3

Sound wave sstrike the tympan icmembrane and be come vib rations.

The sound wave e ne rgy istransfe rre d to the th re e bone so f the midd le e ar,wh ich vib rate .

Ear canal Malle us

Incus

Stape sOval

window

Coch le arne rve

Ve stibu larduct(pe ri lymph)

Coch le arduct(e ndo lymph)

Tympan ic duct(pe ri lymph)

Roundwindow

Tympan icmembrane

Movemento f soundwave s

transmission through the ear

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Sl id e4

Sound wave sstrike the tympan icmembrane and be come vib rations.

The sound wave e ne rgy istransfe rre d to the th re e bone so f the midd le e ar,wh ich vib rate .

The stape s isattache d to the membrane o f the ovalwindow.Vib rationso fthe ovalwindowcre ate flu id wave swith in the coch le a.

Ear canal Malle us

Incus

Stape sOval

window

Coch le arne rve

Ve stibu larduct(pe ri lymph)

Coch le arduct(e ndo lymph)

Tympan ic duct(pe ri lymph)

Roundwindow

Tympan icmembrane

Movemento f soundwave s

Biol 219Lect 19Fall2016 Dr Scott

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transmission through the ear

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Sl id e5

Sound wave sstrike the tympan icmembrane and be come vib rations.

The sound wave e ne rgy istransfe rre d to the th re e bone so f the midd le e ar,wh ich vib rate .

The stape s isattache d to the membrane o f the ovalwindow.Vib rationso fthe ovalwindowcre ate flu id wave swith in the coch le a.

The flu id wave spush onthe fle xib le membrane so f the coch le arduct.Hairce llsbe nd and ion channe lsope n ,cre atingan e le ctrical signal thatalte rsne u ro transmitte r re le ase .

Ear canal Malle us

Incus

Stape sOval

window

Coch le arne rve

Ve stibu larduct(pe ri lymph)

Coch le arduct(e ndo lymph)

Tympan ic duct(pe ri lymph)

Roundwindow

Tympan icmembrane

Movemento f soundwave s

transmission through the ear

©2016PearsonEducation,Inc.

Sl id e6

Sound wave sstrike the tympan icmembrane and be come vib rations.

The sound wave e ne rgy istransfe rre d to the th re e bone so f the midd le e ar,wh ich vib rate .

The stape s isattache d to the membrane o f the ovalwindow.Vib rationso fthe ovalwindowcre ate flu id wave swith in the coch le a.

The flu id wave spush onthe fle xib le membrane so f the coch le arduct.Hairce llsbe nd and ion channe lsope n ,cre atingan e le ctrical signal thatalte rsne u ro transmitte r re le ase .

Ne uro transmitte rre le ase on to se nso ryne u ronscre ate saction po te n tials that trave lth rough the coch le arne rve to the b rain .

Ear canal Malle us

Incus

Stape sOval

window

Coch le arne rve

Ve stibu larduct(pe ri lymph)

Coch le arduct(e ndo lymph)

Tympan ic duct(pe ri lymph)

Roundwindow

Tympan icmembrane

Movemento f soundwave s

transmission through the ear

©2016PearsonEducation,Inc.

Sl id e7

Sound wave sstrike the tympan icmembrane and be come vib rations.

The sound wave e ne rgy istransfe rre d to the th re e bone so f the midd le e ar,wh ich vib rate .

The stape s isattache d to the membrane o f the ovalwindow.Vib rationso fthe ovalwindowcre ate flu id wave swith in the coch le a.

The flu id wave spush onthe fle xib le membrane so f the coch le arduct.Hairce llsbe nd and ion channe lsope n ,cre atingan e le ctrical signal thatalte rsne u ro transmitte r re le ase .

Ne uro transmitte rre le ase on to se nso ryne u ronscre ate saction po te n tials that trave lth rough the coch le arne rve to the b rain .

Ene rgy fromthe wave stransfe rsacross the coch le arduct in to thetympan icductand isd issipate d back in to the midd le e arat theround window.

Ear canal Malle us

Incus

Stape sOval

window

Coch le arne rve

Ve stibu larduct(pe ri lymph)

Coch le arduct(e ndo lymph)

Tympan ic duct(pe ri lymph)

Roundwindow

Tympan icmembrane

Movemento f soundwave s

Biol 219Lect 19Fall2016 Dr Scott

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Figure10.19Signaltransductioninhaircells

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A t rest: About 10% of t he i on channel s are open, and a t oni c si gnal i s sent by t he sensory neuron.

Exci tati on: When t he hai r cel l s bend i n one di rect i on, t he cel l depol ar i zes, w hi ch i ncreases act i on pot ent i al f requency i n t he associ at ed sensory neuron.

Inhi bi ti on: I f t he hai r cel l s bend i n t he opposi t e di rect i on, i on channel s cl ose, t he cel l hyperpol ar i zes, and sensoryneuron si gnal i ng decreases.

Ti p l i nk

St ereoci l i um

Hai r cel l

Some channel sopen.

Pri marysensoryneuron

M ore channel sopen.Cat i on ent rydepol ar i zescel l .

Channel s cl osed. Less cat i on ent ry hyperpol ar i zes cel l .

Act i on pot ent i al s Act i on pot ent i al s i ncrease. No act i on pot ent i al s

mV

A cti on potenti al s i n pri mary sensory neuron Ti me

Exci t at i on opensi on channel s.

Membrane potenti al of hai r cel l

I nhi bi t i on cl osesi on channel s.

Rel ease Rel ease

0

mV

−30

AuditoryPathways

• Cochlea transformssoundwaves intoelectricalsignals

• Primary auditoryneuronstobrain inmedullaoblongata

• Secondary sensoryneuronsproject tonuclei• Synapseinnucleiinmidbrainandthalamusbeforeprojectingintoauditorycortex

• The localizationofasoundsourcerequiressimultaneous inputfrombothears.

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HearingLoss

• Conductive• Notransmissionthrougheitherexternalormiddleear

• Central• Damagetoneuralpathwaybetweenearandcerebralcortexordamagetocortexitself

• Sensorineural• Damagetostructuresofinnerear

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Biol 219Lect 19Fall2016 Dr Scott

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TheVestibularApparatusviaCNVIII

• Series ofinterconnected fluid-filledchambers• Otolith organs

• Saccule andutricle• Linearaccelerationandheadposition

• Semicircular canals• Rotationalacceleration• Filledwithendolymph

• Equilibriumprojectsprimarily tothecerebellum

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The Vestibular Apparatus

The semicircular canals sense three-dimensional rotation.

Biol 219Lect 19Fall2016 Dr Scott

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The otolith organs (utricle and saccule) sense linear movementand position of the head.

Figure10.23Equilibriumpathways

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Vestibular apparatus

Vestibular branch of vestibulocochlearnerve (VIII)

Cerebralcortex

Thalamus

Cerebellum

Reticularformation

Vestibularnuclei ofmedulla

Somaticmotor neurons

controlling eyemovements