Ear OssiclesEar Ossicles

The tympanic cavity contains three small The tympanic cavity contains three small bones: the malleus, incus, and stapesbones: the malleus, incus, and stapes Transmit vibratory motion of the eardrum to the Transmit vibratory motion of the eardrum to the

oval windowoval window Dampened by the tensor tympani and stapedius Dampened by the tensor tympani and stapedius

musclesmuscles

Ear OssiclesEar Ossicles

Figure 15.26

Inner EarInner Ear Bony labyrinthBony labyrinth

Tortuous channels worming their way through the Tortuous channels worming their way through the temporal bonetemporal bone

Contains the vestibule, the cochlea, and the Contains the vestibule, the cochlea, and the semicircular canalssemicircular canals

Filled with perilymphFilled with perilymph Membranous labyrinthMembranous labyrinth

Series of membranous sacs within the bony Series of membranous sacs within the bony labyrinthlabyrinth

Filled with a potassium-rich fluidFilled with a potassium-rich fluid

Inner EarInner Ear

Figure 15.27

The VestibuleThe Vestibule

The central egg-shaped cavity of the bony The central egg-shaped cavity of the bony labyrinthlabyrinth

Suspended in its perilymph are two sacs: the Suspended in its perilymph are two sacs: the saccule and utriclesaccule and utricle

The saccule extends into the cochleaThe saccule extends into the cochlea

The VestibuleThe Vestibule

The utricle extends into the semicircular canalsThe utricle extends into the semicircular canals These sacs:These sacs:

House equilibrium receptors called maculaeHouse equilibrium receptors called maculae Respond to gravity and changes in the position of Respond to gravity and changes in the position of

the headthe head

The VestibuleThe Vestibule

Figure 15.27

The Semicircular CanalsThe Semicircular Canals

Three canals that each define two-thirds of a Three canals that each define two-thirds of a circle and lie in the three planes of space circle and lie in the three planes of space

Membranous semicircular ducts line each Membranous semicircular ducts line each canal and communicate with the utriclecanal and communicate with the utricle

The ampulla is the swollen end of each canal The ampulla is the swollen end of each canal and it houses equilibrium receptors in a region and it houses equilibrium receptors in a region called the crista ampullariscalled the crista ampullaris

These receptors respond to angular movements These receptors respond to angular movements of the headof the head

The Semicircular CanalsThe Semicircular Canals

Figure 15.27

The CochleaThe Cochlea

A spiral, conical, bony chamber that:A spiral, conical, bony chamber that: Extends from the anterior vestibuleExtends from the anterior vestibule Coils around a bony pillar called the modiolusCoils around a bony pillar called the modiolus Contains the cochlear duct, which ends at the Contains the cochlear duct, which ends at the

cochlear apexcochlear apex Contains the organ of Corti (hearing receptor)Contains the organ of Corti (hearing receptor)

The CochleaThe Cochlea

The cochlea is divided into three chambers:The cochlea is divided into three chambers: Scala vestibuliScala vestibuli Scala mediaScala media Scala tympaniScala tympani

The CochleaThe Cochlea

The scala tympani terminates at the round The scala tympani terminates at the round windowwindow

The scalas tympani and vestibuli:The scalas tympani and vestibuli: Are filled with perilymphAre filled with perilymph Are continuous with each other via the helicotremaAre continuous with each other via the helicotrema

The scala media is filled with endolymphThe scala media is filled with endolymph

The CochleaThe Cochlea

The “floor” of the cochlear duct is composed The “floor” of the cochlear duct is composed of:of: The bony spiral laminaThe bony spiral lamina The basilar membrane, which supports the organ The basilar membrane, which supports the organ

of Cortiof Corti The cochlear branch of nerve VIII runs from The cochlear branch of nerve VIII runs from

the organ of Corti to the brain the organ of Corti to the brain

The CochleaThe Cochlea

Figure 15.28

Sound and Mechanisms of Sound and Mechanisms of HearingHearing

Sound vibrations beat against the eardrumSound vibrations beat against the eardrum The eardrum pushes against the ossicles, The eardrum pushes against the ossicles,

which presses fluid in the inner ear against the which presses fluid in the inner ear against the oval and round windowsoval and round windows This movement sets up shearing forces that pull on This movement sets up shearing forces that pull on

hair cellshair cells Moving hair cells stimulates the cochlear nerve Moving hair cells stimulates the cochlear nerve

that sends impulses to the brainthat sends impulses to the brain

Properties of SoundProperties of Sound

Sound is: Sound is: A pressure disturbance (alternating areas of high A pressure disturbance (alternating areas of high

and low pressure) originating from a vibrating and low pressure) originating from a vibrating objectobject

Composed of areas of rarefaction and compressionComposed of areas of rarefaction and compression Represented by a sine wave in wavelength, Represented by a sine wave in wavelength,

frequency, and amplitudefrequency, and amplitude

Properties of SoundProperties of Sound

Frequency – the number of waves that pass a Frequency – the number of waves that pass a given point in a given timegiven point in a given time

Pitch – perception of different frequencies (we Pitch – perception of different frequencies (we hear from 20–20,000 Hz)hear from 20–20,000 Hz)

Properties of SoundProperties of Sound Amplitude – intensity of a sound measured in Amplitude – intensity of a sound measured in

decibels (dB)decibels (dB) Loudness – subjective interpretation of sound Loudness – subjective interpretation of sound

intensityintensity

Figure 15.29

Transmission of Sound to the Transmission of Sound to the Inner EarInner Ear

The route of sound to the inner ear follows this The route of sound to the inner ear follows this pathway:pathway: Outer ear – pinna, auditory canal, eardrumOuter ear – pinna, auditory canal, eardrum Middle ear – malleus, incus, and stapes to the oval Middle ear – malleus, incus, and stapes to the oval

windowwindow Inner ear – scalas vestibuli and tympani to the Inner ear – scalas vestibuli and tympani to the

cochlear duct cochlear duct Stimulation of the organ of CortiStimulation of the organ of Corti Generation of impulses in the cochlear nerveGeneration of impulses in the cochlear nerve

Frequency and AmplitudeFrequency and Amplitude

Figure 15.30

Transmission of Sound to the Transmission of Sound to the Inner EarInner Ear

Figure 15.31

Resonance of the Basilar Resonance of the Basilar MembraneMembrane

Sound waves of low frequency (inaudible):Sound waves of low frequency (inaudible): Travel around the helicotrema Travel around the helicotrema Do not excite hair cellsDo not excite hair cells

Audible sound waves:Audible sound waves: Penetrate through the cochlear ductPenetrate through the cochlear duct Vibrate the basilar membraneVibrate the basilar membrane Excite specific hair cells according to frequency of Excite specific hair cells according to frequency of

the soundthe sound

Resonance of the Basilar MembraneResonance of the Basilar Membrane

Figure 15.32

The Organ of CortiThe Organ of Corti

Is composed of supporting cells and outer and Is composed of supporting cells and outer and inner hair cellsinner hair cells

Afferent fibers of the cochlear nerve attach to Afferent fibers of the cochlear nerve attach to the base of hair cellsthe base of hair cells

The stereocilia (hairs): The stereocilia (hairs): Protrude into the endolymphProtrude into the endolymph Touch the tectorial membraneTouch the tectorial membrane

Excitation of Hair Cells in the Excitation of Hair Cells in the Organ of CortiOrgan of Corti

Bending cilia: Bending cilia: Opens mechanically gated ion channelsOpens mechanically gated ion channels Causes a graded potential and the release of a Causes a graded potential and the release of a

neurotransmitter (probably glutamate)neurotransmitter (probably glutamate) The neurotransmitter causes cochlear fibers to The neurotransmitter causes cochlear fibers to

transmit impulses to the brain, where sound is transmit impulses to the brain, where sound is perceivedperceived

Excitation of Hair Cells in the Organ Excitation of Hair Cells in the Organ of Cortiof Corti

Figure 15.28c

Auditory Pathway to the BrainAuditory Pathway to the Brain

Impulses from the cochlea pass via the spiral Impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei ganglion to the cochlear nuclei

From there, impulses are sent to the:From there, impulses are sent to the: Superior olivary nucleus Superior olivary nucleus Inferior colliculus (auditory reflex center)Inferior colliculus (auditory reflex center)

From there, impulses pass to the auditory cortex From there, impulses pass to the auditory cortex Auditory pathways decussate so that both Auditory pathways decussate so that both

cortices receive input from both earscortices receive input from both ears

Simplified Auditory PathwaysSimplified Auditory Pathways

Figure 15.34

Auditory ProcessingAuditory Processing

Pitch is perceived by: Pitch is perceived by: The primary auditory cortexThe primary auditory cortex Cochlear nuclei Cochlear nuclei

Loudness is perceived by:Loudness is perceived by: Varying thresholds of cochlear cellsVarying thresholds of cochlear cells The number of cells stimulated The number of cells stimulated

Localization is perceived by superior olivary Localization is perceived by superior olivary nuclei that determine soundnuclei that determine sound

DeafnessDeafness Conduction deafness – something hampers Conduction deafness – something hampers

sound conduction to the fluids of the inner ear sound conduction to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles)osteosclerosis of the ossicles)

Sensorineural deafness – results from damage Sensorineural deafness – results from damage to the neural structures at any point from the to the neural structures at any point from the cochlear hair cells to the auditory cortical cellscochlear hair cells to the auditory cortical cells

DeafnessDeafness

Tinnitus – ringing or clicking sound in the ears Tinnitus – ringing or clicking sound in the ears in the absence of auditory stimuliin the absence of auditory stimuli

Meniere’s syndrome – labyrinth disorder that Meniere’s syndrome – labyrinth disorder that affects the cochlea and the semicircular canals, affects the cochlea and the semicircular canals, causing vertigo, nausea, and vomitingcausing vertigo, nausea, and vomiting

Mechanisms of Equilibrium and Mechanisms of Equilibrium and OrientationOrientation

Vestibular apparatus – equilibrium receptors in Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibulethe semicircular canals and vestibule Maintains our orientation and balance in spaceMaintains our orientation and balance in space Vestibular receptors monitor static equilibriumVestibular receptors monitor static equilibrium Semicircular canal receptors monitor dynamic Semicircular canal receptors monitor dynamic

equilibriumequilibrium

Anatomy of MaculaeAnatomy of Maculae

Maculae are the sensory receptors for static Maculae are the sensory receptors for static equilibriumequilibrium Contain supporting cells and hair cellsContain supporting cells and hair cells Each hair cell has stereocilia and kinocilium Each hair cell has stereocilia and kinocilium

embedded in the otolithic membraneembedded in the otolithic membrane Otolithic membrane – jellylike mass studded Otolithic membrane – jellylike mass studded

with tiny CaCOwith tiny CaCO33 stones called otoliths stones called otoliths Utricular hairs respond to horizontal movementUtricular hairs respond to horizontal movement Saccular hairs respond to vertical movementSaccular hairs respond to vertical movement

Anatomy of MaculaeAnatomy of Maculae

Figure 15.35

Effect of Gravity on Utricular Effect of Gravity on Utricular Receptor CellsReceptor Cells

Otolithic movement in the direction of the Otolithic movement in the direction of the kinocilia:kinocilia: Depolarizes vestibular nerve fibersDepolarizes vestibular nerve fibers Increases the number of action potentials generatedIncreases the number of action potentials generated

Movement in the opposite direction:Movement in the opposite direction: Hyperpolarizes vestibular nerve fibersHyperpolarizes vestibular nerve fibers Reduces the rate of impulse propagation Reduces the rate of impulse propagation

From this information, the brain is informed of From this information, the brain is informed of the changing position of the headthe changing position of the head

Effect of Gravity on Utricular Effect of Gravity on Utricular Receptor CellsReceptor Cells

Figure 15.36

Crista Ampullaris and Dynamic Crista Ampullaris and Dynamic EquilibriumEquilibrium

The crista ampullaris (or crista):The crista ampullaris (or crista): Is the receptor for dynamic equilibriumIs the receptor for dynamic equilibrium Is located in the ampulla of each semicircular canalIs located in the ampulla of each semicircular canal Responds to angular movementsResponds to angular movements

Each crista has support cells and hair cells that Each crista has support cells and hair cells that extend into a gel-like mass called the cupulaextend into a gel-like mass called the cupula

Dendrites of vestibular nerve fibers encircle Dendrites of vestibular nerve fibers encircle the base of the hair cellsthe base of the hair cells

Activating Crista Ampullaris Activating Crista Ampullaris ReceptorsReceptors

Cristae respond to changes in velocity of Cristae respond to changes in velocity of rotatory movements of the headrotatory movements of the head

Directional bending of hair cells in the cristae Directional bending of hair cells in the cristae causes:causes: Depolarizations, and rapid impulses reach the brain Depolarizations, and rapid impulses reach the brain

at a faster rateat a faster rate Hyperpolarizations, and fewer impulses reach the Hyperpolarizations, and fewer impulses reach the

brainbrain The result is that the brain is informed of The result is that the brain is informed of

rotational movements of the headrotational movements of the head

Rotary Head MovementRotary Head Movement

Figure 15.37d

Balance and Orientation Balance and Orientation PathwaysPathways

There are three modes There are three modes of input for balance of input for balance and orientationand orientation Vestibular receptorsVestibular receptors Visual receptorsVisual receptors Somatic receptorsSomatic receptors

These receptors allow These receptors allow our body to respond our body to respond reflexively reflexively

Figure 15.38

Developmental AspectsDevelopmental Aspects

All special senses are functional at birthAll special senses are functional at birth Chemical senses – few problems occur until Chemical senses – few problems occur until

the fourth decade, when these senses begin to the fourth decade, when these senses begin to declinedecline

Vision – optic vesicles protrude from the Vision – optic vesicles protrude from the diencephalon during the fourth week of diencephalon during the fourth week of developmentdevelopment These vesicles indent to form optic cups and their These vesicles indent to form optic cups and their

stalks form optic nervesstalks form optic nerves Later, the lens forms from ectodermLater, the lens forms from ectoderm

Developmental AspectsDevelopmental Aspects

Vision is not fully functional at birthVision is not fully functional at birth Babies are hyperopic, see only gray tones, and Babies are hyperopic, see only gray tones, and

eye movements are uncoordinatedeye movements are uncoordinated Depth perception and color vision is well Depth perception and color vision is well

developed by age five and emmetropic eyes developed by age five and emmetropic eyes are developed by year sixare developed by year six

With age the lens loses clarity, dilator muscles With age the lens loses clarity, dilator muscles are less efficient, and visual acuity is are less efficient, and visual acuity is drastically decreased by age 70drastically decreased by age 70

Developmental AspectsDevelopmental Aspects Ear development begins in the three-week Ear development begins in the three-week

embryoembryo Inner ears develop from otic placodes, which Inner ears develop from otic placodes, which

invaginate into the otic pit and otic vesicleinvaginate into the otic pit and otic vesicle The otic vesicle becomes the membranous The otic vesicle becomes the membranous

labyrinth, and the surrounding mesenchyme labyrinth, and the surrounding mesenchyme becomes the bony labyrinthbecomes the bony labyrinth

Middle ear structures develop from the Middle ear structures develop from the pharyngeal pouchespharyngeal pouches

The branchial groove develops into outer ear The branchial groove develops into outer ear structuresstructures