organ of balance and hearing

Organ of balance and hearing

EarEar

SENSES OF HEARING AND BALANCE: THE EAR (cont.)SENSES OF HEARING AND BALANCE: THE EAR (cont.)

Middle ear (Figure 15-11)Middle ear (Figure 15-11) Tiny, epithelium-lined cavity hollowed out of the temporal Tiny, epithelium-lined cavity hollowed out of the temporal

bonebone Contains three auditory ossiclesContains three auditory ossicles

Malleus (hammer): attached to the inner surface of the Malleus (hammer): attached to the inner surface of the tympanic membranetympanic membrane

Incus (anvil): attached to the malleus and stapesIncus (anvil): attached to the malleus and stapes Stapes (stirrup): attached to the incusStapes (stirrup): attached to the incus

Openings into the middle ear cavityOpenings into the middle ear cavity Opening from the external acoustic meatus covered with Opening from the external acoustic meatus covered with

tympanic membranetympanic membrane Oval window: opening into inner ear; stapes fits hereOval window: opening into inner ear; stapes fits here Round window: opening into inner ear; covered by a membraneRound window: opening into inner ear; covered by a membrane Opening into the auditory (eustachian) tubeOpening into the auditory (eustachian) tube

SENSES OF HEARING AND BALANCE: SENSES OF HEARING AND BALANCE: THE EAR (cont.)THE EAR (cont.)

Inner ear (Figure 15-12)Inner ear (Figure 15-12) Structure of the inner earStructure of the inner ear

Bony labyrinth: composed of the vestibule, cochlea, and Bony labyrinth: composed of the vestibule, cochlea, and semicircular canalssemicircular canals

Membranous labyrinth: composed of utricle and saccule inside the Membranous labyrinth: composed of utricle and saccule inside the vestibule, cochlear duct inside the cochlea, and membranous vestibule, cochlear duct inside the cochlea, and membranous semicircular ducts inside the bony semicircular canalssemicircular ducts inside the bony semicircular canals

Vestibule and semicircular canal organs are involved with balanceVestibule and semicircular canal organs are involved with balance Cochlea: involved with hearingCochlea: involved with hearing Endolymph: clear, potassium-rich fluid filling the membranous Endolymph: clear, potassium-rich fluid filling the membranous

labyrinthlabyrinth Perilymph: similar to cerebrospinal fluid; surrounds the Perilymph: similar to cerebrospinal fluid; surrounds the

membranous labyrinth, filling the space between the membranous membranous labyrinth, filling the space between the membranous tunnel and its contents and the bony walls that surround ittunnel and its contents and the bony walls that surround it


Cochlea and cochlear ductCochlea and cochlear duct Cochlea: bony labyrinthCochlea: bony labyrinth Cochlear ductCochlear duct

Lies inside the cochlea; only part of the internal ear concerned with Lies inside the cochlea; only part of the internal ear concerned with hearing; contains endolymphhearing; contains endolymph

Shaped like a triangular tubeShaped like a triangular tube Divides the cochlea into the scala vestibuli, the upper section, and the Divides the cochlea into the scala vestibuli, the upper section, and the

scala tympani, the lower section; both sections filled with perilymphscala tympani, the lower section; both sections filled with perilymph Vestibular membrane: the roof of the cochlear ductVestibular membrane: the roof of the cochlear duct Basilar (spiral) membrane: floor of the cochlear ductBasilar (spiral) membrane: floor of the cochlear duct Organ of Corti: rests on the basilar membrane; consists of supporting Organ of Corti: rests on the basilar membrane; consists of supporting

cells and hair cells; also called cells and hair cells; also called spiral organspiral organ Axons of the neurons that begin around the organ of Corti and extend Axons of the neurons that begin around the organ of Corti and extend

in the cochlear nerve to the brain to produce the sensation of hearingin the cochlear nerve to the brain to produce the sensation of hearing


Sense of hearingSense of hearing Sound is created by vibrationsSound is created by vibrations Ability to hear sound waves depends on volume, pitch, and other Ability to hear sound waves depends on volume, pitch, and other

acoustic propertiesacoustic properties Sound waves must be of sufficient amplitude to move the Sound waves must be of sufficient amplitude to move the

tympanic membrane and have a frequency capable of stimulating tympanic membrane and have a frequency capable of stimulating the hair cells in the organ of Corti (spiral organ) (Figure 15-13)the hair cells in the organ of Corti (spiral organ) (Figure 15-13)

Basilar membrane width and thickness varies throughout its Basilar membrane width and thickness varies throughout its length length High-frequency sound waves vibrate the narrow portion near the High-frequency sound waves vibrate the narrow portion near the

oval windowoval window Low frequencies vibrate the wider, thicker portion near the apex of Low frequencies vibrate the wider, thicker portion near the apex of

the cochleathe cochlea Each frequency stimulates different hair cells and facilitates Each frequency stimulates different hair cells and facilitates

perception of different pitchesperception of different pitches Perception of loudness is determined by movement amplitude; the Perception of loudness is determined by movement amplitude; the

greater the movement, the louder the perceived soundgreater the movement, the louder the perceived sound Hearing results from stimulation of the auditory area of the cerebral Hearing results from stimulation of the auditory area of the cerebral

cortexcortex


Pathway of sound wavesPathway of sound waves Enter external auditory canalEnter external auditory canal Strike tympanic membrane, causing vibrationsStrike tympanic membrane, causing vibrations Tympanic vibrations move the malleus, which moves the Tympanic vibrations move the malleus, which moves the

incus and then the stapesincus and then the stapes The stapes moves against the oval window, which begins The stapes moves against the oval window, which begins

the fluid conduction of sound wavesthe fluid conduction of sound waves The perilymph in the scala vestibuli of the cochlea begins a The perilymph in the scala vestibuli of the cochlea begins a

“ripple” that is transmitted through the vestibular membrane “ripple” that is transmitted through the vestibular membrane to the endolymph inside the duct, to the basilar membrane, to the endolymph inside the duct, to the basilar membrane, and then to the organ of Cortiand then to the organ of Corti

From the basilar membrane, the ripple is transmitted through From the basilar membrane, the ripple is transmitted through the perilymph in the scala tympani and then expends itself the perilymph in the scala tympani and then expends itself against the round windowagainst the round window


Neural pathway of hearingNeural pathway of hearing A movement of hair cells against the tectorial A movement of hair cells against the tectorial

membrane stimulates the dendrites that terminate membrane stimulates the dendrites that terminate around the base of the hair cells and initiates around the base of the hair cells and initiates impulse conduction by the cochlear nerve to the impulse conduction by the cochlear nerve to the brainstembrainstem

Impulses pass through “relay stations” in the nuclei Impulses pass through “relay stations” in the nuclei in the medulla, pons, midbrain, and thalamus in the medulla, pons, midbrain, and thalamus before reaching the auditory area of the temporal before reaching the auditory area of the temporal lobelobe


Vestibule and semicircular canals (Figure 15-Vestibule and semicircular canals (Figure 15-12)12) Vestibule: the central section of the bony Vestibule: the central section of the bony

labyrinth; the utricle and saccule are the labyrinth; the utricle and saccule are the membranous structures within the vestibulemembranous structures within the vestibule

Three semicircular canals Three semicircular canals Each canal is at a right angle to the otherEach canal is at a right angle to the other Membranous semicircular ducts within the canals; Membranous semicircular ducts within the canals;

each contains endolymph and connects with the utricleeach contains endolymph and connects with the utricle Each canal enlarges into an ampulla near junction with Each canal enlarges into an ampulla near junction with

utricleutricle


Sense of balanceSense of balance Static equilibrium: ability to sense head position relative to Static equilibrium: ability to sense head position relative to

gravity or acceleration/deceleration (Figure 15-14)gravity or acceleration/deceleration (Figure 15-14) Movements of the maculae, located in both the utricle and Movements of the maculae, located in both the utricle and

saccule, provide information related to head position or saccule, provide information related to head position or accelerationacceleration

Otoliths are located within the matrix of the maculaOtoliths are located within the matrix of the macula Changing head position produces a change of pressure on the Changing head position produces a change of pressure on the

otolith-weighted matrix, stimulating the hair cells that stimulate the otolith-weighted matrix, stimulating the hair cells that stimulate the receptors of the vestibular nervereceptors of the vestibular nerve

Vestibular nerve fibers conduct impulses to the brain and sense Vestibular nerve fibers conduct impulses to the brain and sense head position and a change in the pull of gravityhead position and a change in the pull of gravity

Righting reflexes: muscular responses to restore the body and its Righting reflexes: muscular responses to restore the body and its parts to their normal position when displaced; caused by stimuli of parts to their normal position when displaced; caused by stimuli of the macula and impulses from proprioceptors and from the eyesthe macula and impulses from proprioceptors and from the eyes


Dynamic equilibrium: needed to maintain balance when the Dynamic equilibrium: needed to maintain balance when the head or body is rotated or suddenly moved; able to detect head or body is rotated or suddenly moved; able to detect changes in direction and rate at which movement occurs (Figure changes in direction and rate at which movement occurs (Figure 15-15)15-15) Depends on the functioning of the cristae ampullaris, Depends on the functioning of the cristae ampullaris,

located in the ampulla of each semicircular ductlocated in the ampulla of each semicircular duct Cupula: gelatinous cap where the hair cells of cristae are Cupula: gelatinous cap where the hair cells of cristae are

embeddedembedded Does not respond to gravityDoes not respond to gravity Moves with the flow of endolymph in the semicircular ductsMoves with the flow of endolymph in the semicircular ducts

Semicircular ducts are arranged at nearly right angles to Semicircular ducts are arranged at nearly right angles to each other to detect movement in all directionseach other to detect movement in all directions

Hair cells bend as cupula moves, producing a receptor Hair cells bend as cupula moves, producing a receptor potential followed by an action potentialpotential followed by an action potential

Action potential passes through the vestibular portion of the Action potential passes through the vestibular portion of the eighth cranial nerve to the medulla oblongataeighth cranial nerve to the medulla oblongata

Sent next to other areas of the brain and spinal cord for Sent next to other areas of the brain and spinal cord for interpretation, integration, and responseinterpretation, integration, and response

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Lecture 16Lecture 16

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Basic Parts of the EarBasic Parts of the Ear

External ear: Hearing; terminates at eardrumExternal ear: Hearing; terminates at eardrum Middle ear: Hearing; contains auditory ossiclesMiddle ear: Hearing; contains auditory ossicles Inner ear: Hearing and balance; interconnecting fluid-Inner ear: Hearing and balance; interconnecting fluid-

filled tunnels and chambersfilled tunnels and chambers

Fig. 19.20

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External EarExternal Ear Auricle or pinna: elastic cartilageAuricle or pinna: elastic cartilage

• External auditory canalExternal auditory canal Tympanic membraneTympanic membrane

External ear Middle ear Inner ear

Auricle(pinna) External auditory canal

Elasticcartilage

Tympanicmembrane

Fig. 19.20

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Middle EarMiddle Ear Auditory or Auditory or

eustachian tubeeustachian tube Opens into Opens into

pharynx, pharynx, equalizes equalizes pressurepressure

Ossicles: Ossicles: malleus, incus, malleus, incus, stapes: transmit stapes: transmit vibrationsvibrations

Oval windowOval window

Fig. 19.21

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Inner EarInner EarLabyrinthLabyrinth BonyBony

Cochlea: HearingCochlea: Hearing Vestibule: BalanceVestibule: Balance

Semicircular canals: BalanceSemicircular canals: Balance MembranousMembranous

Fig. 19.22

Lymphs• Endolymph

– In membranous labyrinth

• Perilymph

– Space between membranous and bony labyrinth

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Structure of CochleaStructure of Cochlea• Membranous labyrinth of cochlea

– Scala vestibuli (perilymph)

– Scala tympani (perilymph)

– Cochlear duct (endolymph)

Fig. 19.27

Fig. 19.27

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Structure of CochleaStructure of Cochlea• Spiral organ (organ of Corti)

– Hair cells

• Stereocilia (microvilli)

– Tectorial membrane• Cochlear nerve

Fig. 19.27

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Effect of Sound Waves on Effect of Sound Waves on Cochlear StructuresCochlear Structures

Fig.19.28

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BalanceBalanceTwo structural and functional components of balance in inner earTwo structural and functional components of balance in inner ear

1.1. Stationary Position and Linear Movement of HeadStationary Position and Linear Movement of Head Evaluates position of head relative to gravityEvaluates position of head relative to gravity Detects linear acceleration and decelerationDetects linear acceleration and deceleration Utricle and sacculeUtricle and saccule

Maculae: Consist of hair cells embedded in statoconic membrane Maculae: Consist of hair cells embedded in statoconic membrane containing otolithscontaining otoliths

Fig. 19.23

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Vestibule in Maintaining Vestibule in Maintaining BalanceBalance

Fig. 19.24

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BalanceBalance2.2. Rotational Rotational

Movements of HeadMovements of Head– Evaluates movements of

head (i.e. angular acceleration)

– 3 semicircular canals

• Ampulla

– Crista ampullaris

– Hair cells

– Cupula

Vestibular nerve + Cochlear nerve = Vestibulocochlear nerve (VIII)Fig. 19.25

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Crista Ampullaris and BalanceCrista Ampullaris and Balance

Fig. 19.26

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Review QuestionReview Question

A person driving a car along a straight street suddenly sees an animal dart in front of the car. He slams on the brakes and manages to stop in time. The sensation of rapid deceleration is generated by the

(a) Bending of the microvilli of the spiral organ(b) Movement of perilymph fluid in the vestibule(c) Movement of the gelatinous covering over the maculae(d) Movement of endolymph fluid in the semicircular canals(e) Movement of the cupula

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Points to RememberPoints to Remember

Inner ear functions for hearing and balance.Inner ear functions for hearing and balance. Sound waves enter the external auditory canal, Sound waves enter the external auditory canal,

impact tympanic membrane, vibrate middle ear impact tympanic membrane, vibrate middle ear ossicles, strike oval window, create waves in ossicles, strike oval window, create waves in perilymph of scala vestibuli, increase pressure in perilymph of scala vestibuli, increase pressure in endolymph in cochlear duct, membrane endolymph in cochlear duct, membrane supporting hair cells vibrates, hair cells supporting hair cells vibrates, hair cells stimulated, vibrations transferred to perilymph of stimulated, vibrations transferred to perilymph of scala tympani, travel to round window and scala tympani, travel to round window and dampened.dampened.

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Points to RememberPoints to Remember

Static balance is orientation of body relative to Static balance is orientation of body relative to pull of gravity - maculae of utricle and saccule pull of gravity - maculae of utricle and saccule (static labyrinth) are sense organs of static (static labyrinth) are sense organs of static balance.balance.

Kinetic balance is maintenance of body position Kinetic balance is maintenance of body position in response to movement - crista ampullaris in in response to movement - crista ampullaris in semicircular canals (kinetic labyrinth) are sense semicircular canals (kinetic labyrinth) are sense organs of kinetic balance.organs of kinetic balance.

organ of balance and hearing

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