Hearing

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Hearing. Maddie, Emma, Kelly, Meg. Equilibrium sensations – inform us of the position of the head in space by monitoring gravity, linear acceleration, and rotation Hearing – enables us to detect and interpret sound waves - PowerPoint PPT Presentation

Text of Hearing

Hearin

HearingMaddie, Emma, Kelly, MegUnderlined words guided notes FITBBold vocab1Equilibrium sensations inform us of the position of the head in space by monitoring gravity, linear acceleration, and rotation

Hearing enables us to detect and interpret sound waves

Hair cells the receptor mechanism for both equilibrium and hearing (respond to different stimuli and thus provide input)Ear is divided into 3 regions:External EarMiddle EarInner Ear

External EarVisible portion of the earCollects and directs sound waves toward the middle earAuricle- protects the opening of the canal and provides directional sensitivityAuricle- blocks sounds from behind while sounds from the front are channeled into the external acoustic canalExternal Acoustic Canal- passageway that ends at the tympanic membrane (ear drum)Tympanic membrane- separates external ear from middle earCeruminous glands- glands along the external acoustic canal that secrete a waxy material, cerumen, to block out foreign objects and increase sensitivityMiddle Ear aka tympanic cavityCommunicates with the nasopharynx through the auditory tube With the mastoid air cells through small connectionsAuditory tube- equalizes the pressures on either side of the tympanic membrane (ear drum)Otitis media- a middle ear infection caused by invasion of microorganismsMiddle Ear- contains three tiny ear bones called auditory ossiclesAuditory ossicles:Malleus (hammer)-attaches to tympanic membraneIncus (anvil)- attaches malleus to the stapesStapes inner ossicle, bound to the oval window which surrounds the inner earAuditory ossicles-Act as levers that conduct vibrations to the inner earProduces rocking motionTensor tympani muscle contracts and pulls malleus medially and stiffens the tympanic membrane and reduces movement for loud soundsStapedius muscle pulls the stapes, reducing their movement at the oval window Inner Ear4 layers

Outer layer Bony Labyrinth made up of dense bone

2nd layer Perilymph liquid in between the bony and membranous labyrinths

3rd layer Membranous labyrinth delicate, interconnected network of fluid filled tubes (receptors of the inner ear are found within these tubes)

Inner layer Endolymph a fluid with electrolyte concentrationsCross section pic pg 57511

KEYLateralSemicircular canalCristae within ampullaeMaculaeEndolymphatic sacCochleaVestibular duct Cochlear duct Organ of CortiTympanicductPosterior(a)(b)AnteriorSemicircularductsVestibuleSacculeUtricleEndolymphPerilymphMembranouslabyrinthBony labyrinthMembranous labyrinthBony labyrinthDiagram from 575 goes here12Inner EarBony labyrinth subdivided intoVestibule consists of the saccule and the utricle (membranous sacs)3 semicircular canals enclose semicircular ductsCombination of vestibule and semicircular canals is called the vestibular complexCochlea spiral shaped bony chamber that contains the cochlear ductInner EarBony labyrinth consists of dense bone everywhere except the round window and oval windowEquilibriumEquilibrium sensations provided by receptors of the vestibular complexSemicircular Ducts (Anterior, Posterior, Lateral semicircular)Sensory receptors in the semicircular ducts respond to rotation movements of the headEach semicircular duct contains an ampulla (expanded region that contains the receptors)Crista region in the wall of the ampulla that contains the receptorsBound to cupula

EquilibriumEach hair cell in the vestibule contains a kinocilium (single large cilium)EquilibriumHair cells (receptors) are active during a movement, quiet when the body is motionlessFree surface of each hair cell supports 80-100 long stereocilia (resemble microvilli)Hair cells provide information about the direction and strength of mechanical stimuliStimuli involved varies by hair cells locationGravity or acceleration in the vestibuleRotation in the semicircular canalsSound in the cochleaEquilibriumMovement of receptors controlled by three rotational planesHorizontal rotation (ex. Shaking your head no) stimulates the hair cells of the lateral semicircular ductVertical movement (ex. Nodding yes) excites the anterior ductTilting your head from side to side activates receptors in the posterior ductFunction provide equilibrium sensationsUtricle and Saccule are connected by a slender passageway that is continuous with the narrow endolymphatic duct, which ends in the endolymphatic sacThe Utricle and SacculeHair cells of utricle and saccule are clustered in oval structures called maculaeHair cell processes are embedded in a gelatinous mass (contains densely packed calcium carbonate crystals known as statoconia)Otolith Whole complex (gelatinous matrix + statoconia)The Utricle and Saccule

Gelatinous materialStatoconiaNerve fibersOtolithGravityGravityReceptor output increasesOtolith moves downhill, distorting hair cell processes (b) Structure of a maculaSTEP1STEP2Head in the anatomical positionHead tilted posteriorly(a)(c)

Macula of SacculeWhen your head is in the normal, upright position, the statoconia sit atop the macula (their weight pushes the hair cell processes down rather than one side or another)

When your head is tilted, the pull of gravity on the statoconia shifts them to the side, distorting the hair cell processes (alerts the central nervous system that the head is no longer level)Macula of SacculeUnder normal circumstances, body can distinguish between sensations of tilting and linear acceleration through visual information (amusement park rides confuse your sense of equilibrium because of the change in position and acceleration with restricted/misleading visual information)Pathways for Equilibrium SensationsSensory fibers contained within the vestibular nuclei 4 functions of the 2 vestibular nucleiIntegrating sensory information about balance and equilibrium that arrives from both sides of the headSend information to cerebral cortex and cerebellum of brainReflexive motor commands issued by vestibular nuclei are distributed to motor nuclei for cranial nerves involved with eye, head, and neck movementsAutomatic movements of eye that occur in response to sensations of motion directed by the superior colliculi of the mesencephalon (in an attempt to keep your gaze focused on a specific point, despite changes in body position and orientation)Nystagmus condition in which people have trouble controlling their eye movementsPathways for Equilibrium Sensations

Vestibular ganglionVestibuleSemicircularcanalsCochlearbranchVestibularbranchXI VI IV IIIRed nucleusTo ipsilateral superior colliculusand relay to cerebral cortexVestibular nucleusTo cerebellumVestibulospinal tractsVestibulocochlearnerve (VIII) Receptors responsible for hearing are hair cells in the cochlear duct

Auditory ossicles convert pressure fluctuation in the air into fluctuation in the perilymph of the cochlea (outside pressure to inside pressure)HearingFrequency of sound determined from which part of cochlear duct is stimulated

Volume is determined from how many hair cells are stimulatedHearingCochlear duct is between perilymph ducts: vestibular duct and tympanic duct

Outer surfaces encased by bony labyrinth everywhere except bases of ducts

Ducts are connected and actually form one long ductThe Cochlear DuctHairs are located in the organ of Corti in longitudinal rows

When the basilar membrane (which the hairs are located on) bounces, the hair cells are distorted by pressing against the upper membrane (tectorial membrane)The Cochlear DuctHearing is perception of soundSine waves: S-shaped curves created by high and low pressure, travel in cyclesTravel at about 768 mph: speed of soundAn Introduction to Sound31Wavelength inversely related to frequency (number of waves that pass through reference point for certain amount of time)Pitch=sensory response to frequencyAmplitude=intensity of sound, energy contentCycles per second=hertz, HzSound energy reported in decibelsAn Introduction to SoundWith the right combination of frequency and amplitude, object will vibrate at same frequency as sound: called resonance

To hear sound, tympanic membrane must vibrate in resonance with sound wavesAn Introduction to Sound

The Hearing Process Sound waves arrive at the tympanic membraneEnter external acoustic canal and travel to tympanic membrane

Movement of the tympanic membrane causes displacement of the auditory ossiclesa) Tympanic membrane is the surface for sound collectionb) Resonate with frequencies ~20-20,000 Hzc) When tympanic membrane vibrates, inner ossicles also vibrate= amplify the sound

Include diagram from book353. Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular ducta) Because liquid is incompressible, pressure can only be relieved at the round windowb) Stapes vibrate and creates pressure waves in the perilymph

The Hearing Process 4. The pressure waves distort the basilar membrane on their way to the round window of the tympanic ducta) Pressure waves travel around perilymph and reach round windowb) As they do this, they disrupt the basilar membranec) High frequencies vibrate the basilar membrane near oval windowd) Lower the frequency, longer wavelength and further from oval window is the maximum distortione) Frequency translated to position along basilar membranef) Amount of movement depends on force of sound

The Hearing Process 5. Vibration of the basilar membrane causes vibration of hair cells against the tectorial membranea) Vibration of basilar membrane moves hair cells against tectorial membraneb) Ion channels open, depolarizes hair cellsc) Leads to release of neurotransmitters/ stimulates sensory organsd) Hairs are stimulated in rowse) Number of cells responding indicates intensity of sound

The Hearing Process Region and intensity of stimulated area is relayed to the CNS