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Auditory Systemsystem AuditoryAuditory systemsystem OrganOrgan ofof hearinghearing AuditoryAuditory systemssystems isis anan engineeringengineering masterpiecemasterpiece SizeSize ofof aa peapea DetectsDetects vibrationsvibrations asas smallsmall asas thethe sizesize ofof anan atomatom RespondsResponds 10001000 timestimes fasterfaster thanthan thethe visualvisual photoreceptorsphotoreceptors MuchMuch ofof humanhuman communicationscommunications isis mediatedmediated byby thethe auditoryauditory system,system, includingincluding musicmusic RoleRole ofof AuditionAudition inin BehaviorBehavior LanguageLanguage LocalizationLocalization ofof aa soundsound sourcesource inin thethe absenceabsence ofof visualvisual cuescues SpeciesSpecies --specificspecific vocalizationsvocalizations ProsodyProsody –– emotionalemotional contentcontent ofof languagelanguage AppreciationAppreciation ofof musicmusic PeriodicPeriodic condensationcondensation andand rarefactionrarefaction ofof airair moleculesmolecules areare detecteddetected byby thethe auditoryauditory systemsystem ComplexComplex soundssounds can be broken down into the fundamental frequency components SoundSound == pressurepressure waveswaves generatedgenerated byby vibratingvibrating airair moleculesmolecules WaveformWaveform (amplitude/time)(amplitude/time) PhasePhase AmplitudeAmplitude (dB)(dB) FrequencyFrequency (Hz)(Hz) –– spectrumspectrum 2020 HzHz toto 2020 kHzkHz FlowFlow ofof informationinformation ExternalExternal andand middlemiddle earsears collectcollect soundsound waveswaves andand amplifyamplify theirtheir pressurepressure SoundSound energyenergy inin thethe airair isis transmittedtransmitted toto thethe fluidfluid-- filledfilled cochleacochlea ofof thethe innerinner earear InIn innerinner earear aa seriesseries ofof biomechanicalbiomechanical processesprocesses breakbreak upup thethe signalsignal intointo simplersimpler sinusoidalsinusoidal componentscomponents Frequency,Frequency, amplitude,amplitude, phasephase ofof thethe originaloriginal signalsignal areare allall faithfullyfaithfully transducedtransduced byby thethe sensorysensory cellscells andand encodedencoded byby thethe electricalelectrical activityactivity ofof nervesnerves SeveralSeveral levelslevels ofof centralcentral processingprocessing inin CNSCNS MajorMajor componentscomponents ofof thethe earear EExternalxternal (outer)(outer) earear ,, aurisauris externaexterna auricle (pinna) external acoustic meatus (ear canal) MMiddleiddle earear ,, aurisauris mediamedia tympanic membrane (ear drum) tympanic cavity auditory (eustachian) tube auditory ossicles IInternalnternal (inner)(inner) earear ,, aurisauris internainterna -- auditoryauditory andand vestibularvestibular portionsportions osseous labyrinth membranous labyrinth EarEar overviewoverview –– 33 componentscomponents MajorMajor componentscomponents ofof thethe earear (Lat.(Lat. auris)auris) External ear – auricle (pinna) Thin skin with fine hairs Elastic fibrocartilage Tuberculum Lobule of auricle Auricular tubercle (of Tragus Darwin ) Ligaments of auricle - extrinsic (connect the auricle with the temporal bone ) and Antihelix Antitragus intrinsic (connect individual Helix Lobulus auricular cartilages ) External ear – muscles M. auricularis sup. EExtrinsicxtrinsic aauricularuricular musclesmuscles -- auricularesauriculares anterior,anterior, superiorsuperior andand posteriorposterior M. helicis major IIntrinsicntrinsic aauricularuricular M. auricularis ant. musclesmuscles -- helicishelicis majormajor andand minor,minor, tragicus,tragicus, M. helicis minor antitragicus,antitragicus, M.antitragicus transversustransversus auriculaeauriculae and obliquus auriculae M.tragicus and obliquus auriculae InnervationInnervation -- CNCN VIIVII External ear – blood supply External ear – sensory innervation External ear – external acoustic meatus Cartilaginous part – outer (~8 mm long), Osseous part – inner (~16 mm long), Thin skin; the thicker cerumen -producing ear canal Skin has fine hairs, tragi Sebaceous glands in the hair follicles Ceruminous glands ear wax, cerumen ConductiveConductive hearinghearing lossloss OcclusionOcclusion ofof thethe auditoryauditory canalcanal byby cerumencerumen The tip of a water -filled syringe is placed just inside the ear canal, and a stream of warm water is instilled into the canal to remove earwax. MiddleMiddle earear FunctionFunction -- soundsound conductionconduction apparatusapparatus ComponentsComponents tympanic membrane tympanic cavity auditory (eustachian) tube auditory ossicles TTympanicympanic membranemembrane Separates the tympanic cavity from the external acoustic meatus Diameter 10 -11 mm longest/8 -9 mm shortest Parts pars flaccida (Schrapnell ’s membrane ) pars tensa → umbo Layers cuticular layer - continuous with the thin skin of the meatus (keratinized) fibrous layer – absent in pars flaccida radiate fibers circular fibers mucous layer - part of the mucosa of the tympanic cavity (single layer of flat cells, no ciliated cells OtoscopicOtoscopic appearanceappearance ofof thethe rightright tympanictympanic membranemembrane TTympanicympanic membranemembrane Otoscope The inner surface of the membrane is convex and the point of greatest convexity is termed the umbo ConductiveConductive hearinghearing lossloss DamageDamage toto thethe tympanictympanic membranemembrane perforation of the tympanic membrane this ear drum has a 20% perforation in the posterior portion of this right ear drum this hole would usually be repaired with a graft placed under the ear drum...an operation called a tympanoplasty Mainly innervated by the auriculotemporal nerve, and appears to perceive only pain ConductiveConductive hearinghearing lossloss OtitisOtitis mediamedia inflammation of the middle ear cleft immobile tympanic membrane, which can be dull, opaque, red, bulging, or even show pus through it a demonstrable conductive hearing loss TympanicTympanic cavitycavity –– 1.51.5 cmcm 3,, airair --filledfilled Epitympanic recess (the attic) - above the level of the membrane, which contains the upper half of the malleus and most of the incus Tympanic cavity proper (mesotympanum ) - opposite the tympanic membrane Hypotympanum (hypotympanic recess) – connected to the eustachian tube TympanicTympanic cavitycavity –– 66 wallswalls LLateralateral wallwall –– pariesparies membranaceusmembranaceus membrana tympani et recessus epitympanicus MMedialedial wallwall –– pariesparies labyrinthicuslabyrinthicus SSuperioruperior wall,wall, roofroof –– pariesparies tegmentalistegmentalis tegmen tympani → otogenic meningitis IInferiornferior wall,wall, floorfloor –– pariesparies jugularisjugularis canaliculus tympanicus AAnteriornterior wallwall –– pariesparies caroticuscaroticus PPosteriorosterior wallwall –– pariesparies mastoideusmastoideus antrum mastoideum TympanicTympanic cavitycavity CourseCourse ofof facialfacial nervenerve inin thethe tympanictympanic cavitycavity medial Chorda tympani lateral CourseCourse ofof chordachorda tympanitympani nervenerve BrainBrain isis inin proximityproximity toto thethe cellscells ofof thethe temporaltemporal bonebone →→ infectioninfection propagationpropagation AuditoryAuditory (Eustachian,(Eustachian, pharyngotympanicpharyngotympanic )) tubetube Connects middle ear with nasopharynx Ventilates middle ear and air cells Equalizes pressure between middle ear & atmosphere Drains middle ear spaces Creates a barrier to ascending infection (more horizontal and shorter in infants) cartilaginous part - – 24 mm bony part - – 12 mm MiddleMiddle earear -- ossiclesossicles Malleus (Lat., hammer ) - the largest, 8 -9 mm long head, caput mallei neck, collum mallei handle, manubrium mallei anterior and lateral processes Incus (Lat. , anvil ) body, corpus incudis long process, crus longum lenticular process short process, crus breve Stapes (Lat. , stirrup ) head, caput stapedis limbs (crura) – anterior & posterior base, basis stapedis MiddleMiddle earear –– ligamentsligaments && jointsjoints body of incus long limb ConductiveConductive hearinghearing lossloss OtosclerosisOtosclerosis aa bonybony ankylosisankylosis (knee)(knee) knitsknits thethe bonebone ofof thethe middlemiddle earear toto thethe stapes,stapes, preventingpreventing normalnormal transmissiontransmission ofof soundsound fromfrom thethe eardrumeardrum intointo thethe innerinner earear ImportanceImportance ofof middlemiddle earear forfor hearinghearing ExternalExternal earear MiddleMiddle EarEar InnerInner earear Avoid reflection airborne environment aqueous environment Air -fluid boundary Low impedance High impedance Because of the marked difference in elasticity and density betwe en air and fluid, almost 99 % of acoustic energy is reflected back at the air -fluid interface between the middle ear and inner ear Middle ear ensures transmission of the sound energy across the air –fluid boundary by boosting the pressure measured at the tympanic membrane almost 200 -fold by the time it reaches the inner ear MiddleMiddle earear -- musclesmuscles Stapes - stapedius muscle – CN VII Malleus - tensor tympani muscle – CN V ReflexivelyReflexively activatedactivated byby loudloud noisenoise ProtectionProtection againstagainst loudloud noisenoise damagedamage StapediusStapedius && tensortensor tympanitympani musclesmuscles tendon of tensor tympani m. tensor tympani m. stapedius tendon of stapedius StapediusStapedius && tensortensor tympanitympani musclesmuscles tendon of tensor tympani tendon of stapedius
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