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  (pinna)  external acoustic meatus ( canal)  MMiddleiddle earear ,, aurisauris mediamedia  tympanic membrane (ear drum)   auditory (eustachian) tube  auditory  IInternalnternal (inner)(inner) earear ,, aurisauris internainterna-- auditoryauditory andand vestibularvestibular portionsportions  osseous labyrinth  EarEar overviewoverview –– 33 componentscomponents MajorMajor componentscomponents ofof thethe earear (Lat.(Lat. auris)auris) External ear – auricle (pinna)

 Thin with fine  Elastic fibrocartilage Tuberculum  Lobule of auricle  Auricular tubercle (of Darwin )  Ligaments of auricle - extrinsic (connect the auricle with the temporal ) and intrinsic (connect individual 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  Skin has fine hairs, tragi  Sebaceous glands in the 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 . 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

Mainly innervated by the auriculotemporal , and appears to perceive only pain ConductiveConductive hearinghearing lossloss

 OtitisOtitis mediamedia  inflammation of the cleft  immobile tympanic membrane, which can be dull, opaque, red, bulging, or even show pus through it  a demonstrable conductive loss TympanicTympanic cavitycavity –– 1.51.5 cmcm 3,, airair --filledfilled

 (the attic) - above the level of the membrane, which contains the upper half of the and most of the  Tympanic cavity proper (mesotympanum ) - opposite the tympanic membrane  Hypotympanum (hypotympanic recess) – connected to the 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  (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  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 - – CN VII Malleus - – CN V

 ReflexivelyReflexively activatedactivated byby loudloud noisenoise  ProtectionProtection againstagainst loudloud noisenoise damagedamage StapediusStapedius && tensortensor tympanitympani musclesmuscles

of tensor tympani

m. tensor tympani

m. stapedius

tendon of stapedius StapediusStapedius && tensortensor tympanitympani musclesmuscles

tendon of tensor tympani tendon of stapedius TheThe stapediusstapedius reflexreflex HyperacusisHyperacusis

 DefinitionDefinition  abnormalabnormal sensitivitysensitivity toto everydayeveryday soundsound levelslevels oror noises,noises, oftenoften sensitivitysensitivity toto higherhigher pitchedpitched sounds,sounds, inin thethe presencepresence ofof essentiallyessentially normalnormal hearinghearing  CauseCause  damagedamage toto thethe nervenerve toto thethe stapediusstapedius oror thethe stapediusstapedius muscle,muscle, therebythereby causingcausing faultyfaulty amplificationamplification ofof soundssounds Note: Meneire’s innervated by VII, IX, and X

cerumen, media, Meniere’s disease foreign bodies IInnernner earear

 LLocatedocated withinwithin thethe petrouspetrous portionportion ofof thethe temporaltemporal bonebone  CContainsontains 22 systemssystems ofof canalscanals oror cavitiescavities  osseousosseous (bony)(bony) labyrinthlabyrinth -- protectiveprotective ““capsulecapsule ””  membranousmembranous labyrinthlabyrinth (within(within bony)bony) -- ““workingworking ”” partpart Location of labyrinth within the petrous portion of the

anterior

medial

lateral

posterior BonyBony vsvs membranousmembranous labyrinthlabyrinth

Bony labyrinth Membranous labyrinth SemicircularSemicircular canalscanals SemicircularSemicircular ductsducts

VestibulumVestibulum Sacculus ( anterior cavity ) → Utriculus (posterior cavity ) → semicircular ducts CochleaCochlea CochlearCochlear ductduct

PerilymphPerilymph EndolymphEndolymph bony ComponentsComponents ofof thethe labyrinth

membranous

sensory PerilymphPerilymph vsvs endolymphendolymph

 BBonyony labyrinthlabyrinth –– perilymphperilymph  similar in ionic composition to and extracellular fluid of other tissues, but contains little protei n  emerges from the microvasculature of the periosteum and is drained by a perilymphatic duct into the adjoining subarachnoid space  suspends and supports the closed membranous labyrinth, protecting it from the hard wall of the  MMembranousembranous labyrinthlabyrinth –– endolymphendolymph  high K+ (150 mM) and low Na + (16 mM) similar to intracellular fluid  generated largely by capillaries in the stria vascularis in the wall of the cochlear duct  drained from the vestibule into venous sinuses of the dura mater by the small InnerInner earear fluidsfluids

Na + K+ Ca++ Protein mEq/l mEq/l MM g/l 140 5 0.68 200 5 150 0.023 30 Plasma 145 4 2.6 4300 CSF 140 3 1.2 30 TheThe membranousmembranous labyrinthlabyrinth includesincludes thethe sensesense organsorgans forfor equilibriumequilibrium && hearinghearing

 OOrgansrgans forfor thethe sensesense ofof equilibriumequilibrium andand balancebalance  SacculeSaccule →→ maculamacula  UtricleUtricle →→ maculamacula  SSemicircularemicircular ductsducts →→ cristacrista ampullarisampullaris inin ampullaampulla  OrganOrgan forfor thethe sensesense ofof hearinghearing  CCochleaochlea LiquorLiquor ofof innerinner earear

Endo lymphatic duct Perilymphatic duct ComponentsComponents ofof thethe labyrinth CCochleaochlea (L.,(L., snail)snail)

 3535 mmmm inin lengthlength  MMakesakes 2⅓ twotwo --andand --oneone --halfhalf turnsturns aroundaround aa bonybony corecore –– modiolusmodiolus  MModiolusodiolus containscontains bloodblood vesselsvessels andand surroundssurrounds thethe cellcell bodiesbodies andand processesprocesses ofof thethe acousticacoustic branchbranch ofof CNCN VIIIVIII inin thethe cochlearcochlear ((spiralspiral )) ganglionganglion ModiolusModiolus (Lat.,(Lat., ModiolusModiolus && cochlearcochlear nervenerve Spaces of

 SScalacala vestibulivestibuli -- perilymphperilymph  SScalacala mediamedia (c(c ochlearochlear ductduct )) -- endolymphendolymph  SScalacala tympanitympani -- perilymphperilymph

Scala vestibuli and scala tympani are in reality one long tube, beginning at the and ending at the . They communicate at the apex of the cochlea via an opening known as the . 22 membranesmembranes separateseparate scalascala mediamedia fromfrom thethe otherother compartmentscompartments

(vestibular) basement membrane with simple squamous epithelium on each side

Organ of hearing

thick basal lamina

zona arcuata

zona pectinata Although the cochlea narrows from base to apex, the widens toward the apex. The helicotrema is the continuity between the scala vestibuli and the scala tympani. Cross-section through cochlea

= Scala media SStriatria vascularisvascularis

 EEpitheliumpithelium responsibleresponsible forfor Reissner’s () productionproduction andand maintenancemaintenance ofof thethe endolymphendolymph forfor thethe entireentire membranousmembranous labyrinthlabyrinth Stria vascularis  EEnclosesncloses aa networknetwork ofof capillariescapillaries  CCellsells withwith manymany deepdeep basalbasal Spiral prominence infoldingsinfoldings ofof theirtheir plasmaplasma membranesmembranes →→ numerousnumerous mitochondriamitochondria  FluidFluid andand K+K+ ionsions pumpedpumped fromfrom thethe capillariescapillaries byby thethe epithelialepithelial cellscells areare releasedreleased inin thethe cochlearcochlear ductduct SStriatria vascularisvascularis && diseasedisease

 CONGENITALCONGENITAL HEARINGHEARING LOSSLOSS  DerivedDerived fromfrom ectoderm,ectoderm, neuralneural crestcrest cellscells andand mesenchymemesenchyme  FailureFailure ofof NCNC migrationmigration resultsresults inin absenceabsence ofof endolymphendolymph productionproduction  HairHair cellscells dondon ’’tt survivesurvive SSpiralpiral organorgan (organ(organ ofof Corti)Corti) OrganOrgan ofof CortiCorti == sensorysensory ++ supportingsupporting cellscells (~150(~150 µµµµµµmm wide)wide)

TheThe sitesite ofof mechanochemicalmechanochemical transductiontransduction HairHair cellscells ~16,000/cochlea

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. HairHair cellscells –– auditoryauditory receptorreceptor cellscells

 OuterOuter hairhair cellscells (OHC)(OHC) –– inin 33 rowsrows  IInnernner hairhair cellscells (IHC)(IHC) –– inin 11 rowrow HairHair cellscells –– 11 KinociliumKinocilium ++ 3030 stereociliastereocilia K

Functions of kinocilia are unclear, they disappear shortly after birth in

Kandel, Schwartz, Jessell; Principles of Neural Science, 4 th ed. LinksLinks betweenbetween stereociliastereocilia

Current Opinion in Neurobiology Volume 12, Issue 4 , 1 August 2002, Pages 380-386 StereociliaStereocilia containcontain actinactin filamentsfilaments SupportingSupporting cellscells ofof thethe organorgan ofof CortiCorti

 Pillar cells - filled with tonofibrils ; converge to form the fluid -filled tunnel of Corti  Phalangeal (Deiters') cells – support IHC & OHC  Hensen ’s cells – columnar cells, outer to the outer phalangeal cells; outer border of the  Border cells (inner side) & Claudius cells (outer side) – form external borders of the organ of Corti TTectorialectorial membranemembrane

Gelatinous structure with embedded filamentous elements. It extends over the free surface of the organ of Corti. The hairs of the hair cells are attached to it. RelationsRelations betweenbetween pp halangealhalangeal && hairhair cellscells

 OuterOuter phalangealphalangeal cellscells havehave processesprocesses →→ OHCOHC  InnerInner phalangealphalangeal cellscells dodo notnot havehave processesprocesses →→ IHCIHC

Bony  H – helicotrema cochlea  M –  SG –  VN – n.vestibulocochlearis  FN –  OC – organ of Corti  SV – scala vestibuli  ST – scala tympani  CD – cochlear duct  AO – auditory ossicle  А – ampulla of a semicircular canal  CA – vestibulum ganglion spirale cochlea Bony Lamina spiralis ossea Fibers of Fibers cochlear tympani nerve scala spiralis limbus limbus membrane membrane tectorial Organ of Corti Organ basilar epithelium cochlear i.spiraleLig. vestibuli duct scala prominentia prominentia membrane vestibular spiralis vascularis stria cochlea Bony OrganOrgan ofof CortiCorti

sulcus sulcus spiralis spiralis int. Cells of cuniculus ext. Outer hair tectorial Claudius medius cells (Nuel) membrane Cells of Hansen Inner hair limbus cell spiralis Border cuniculus cell Internal ext. sulcus cells cuniculus med. (Nuel) Tunnel of Fibers of Corti cochlear Lig. spirale nerve Outer Inner Inner Outer pillar pillar phalangeal Cells of basilar phalangeal cell cell cells Lamina Boettcher membrane cells spiralis (Deiters) ossea BasilarBasilar membranemembrane isis displaceddisplaced byby energyenergy (sound)(sound) waveswaves fromfrom thethe stapesstapes

Basilar membrane BasilarBasilar membranemembrane displacementdisplacement isis convertedconverted intointo electricalelectrical signalssignals byby thethe organorgan ofof CortiCorti MechanoelectricalMechanoelectrical transductiontransduction

 ChangesChanges inin soundsound waveswaves  BasilarBasilar membranemembrane vibrationsvibrations  IonIon ChannelsChannels openopen  DepolarizationDepolarization  ActionAction potentialpotential MechanoelectricalMechanoelectrical transductiontransduction && hairhair cellscells

DrugDrug --inducedinduced damagedamage toto hairhair cellscells

 SomeSome antibioticsantibiotics damagedamage OHCsOHCs  HearingHearing abnormalitiesabnormalities producedproduced byby antibioticsantibiotics isis aa consequenceconsequence ofof damagedamage toto thethe cochlearcochlear amplifieramplifier HairHair cellscells areare innervatedinnervated byby thethe spiralspiral ganglionganglion

30,000 bipolar neurons ReceptorsReceptors ofof sensorysensory systemssystems -- primaryprimary sensorysensory neuronsneurons

pseudounipolar

part of PNS (except jaw proprioception)

bipolar

part of CNS Nerve supply to hair cells

 90% of spiral ganglion neurons (type I cells) innervate IHC  each IHC receives contacts from about 10 fibers; each fiber contacts only 1 IHC

 10% of spiral ganglion neurons (type II cells) innervate OHC  each fiber diverges to innervate many OHC Efferent fibers to hair cells originate in the contralateral superior olive in the pons and and terminate on OHC and the afferent terminal boutons innervating IHC. Efferent fibers have an inhibitory effect on auditory stimuli. TypesTypes ofof hearinghearing lossloss

 ConductiveConductive hearinghearing lossloss -- variousvarious problemsproblems inin thethe middlemiddle earear whichwhich cancan reducereduce conductionconduction ofof vibrationsvibrations byby thethe chainchain ofof ossiclesossicles fromfrom thethe tympanictympanic membranemembrane toto thethe ovaloval windowwindow  SensorineuralSensorineural hearinghearing lossloss –– isis duedue toto defectsdefects inin anyany structurestructure oror cellcell fromfrom thethe cochleacochlea toto auditoryauditory centerscenters ofof thethe brain,brain, butbut commonlycommonly involvesinvolves lossloss ofof hairhair cellscells oror nervenerve degenerationdegeneration ((cancan bebe congenitalcongenital oror acquiredacquired )) PatientsPatients withwith severesevere sensorineuralsensorineural deafnessdeafness maymay bebe helpedhelped byby cochlearcochlear implantsimplants

prosthetic electrode array BasilarBasilar membranemembrane isis thethe mechanicalmechanical analyzeranalyzer ofof soundsound -- tonotopytonotopy A traveling wave is shown at a given instant along the cochlea, which has been uncoiled. The graphs profile the amplitude of the traveling wave along the basilar membrane for different frequencies and show that the position where the trave ling wave reaching its maximum amplitude varies directly with the frequency of stimulat ion.

AuditoryAuditory systemsystem Spiral Ganglion

Cranial Nerve VIII Dorsal Cochlear Nuc Cochlear Nucleus

Superior Olivary Nuc

Lateral Lemniscus

Inferior Colliculus Ventral Cochlear Nuc Medial Geniculate Origin: Spiral ganglion Course: CNVIII, auditory pathway, auditory cortex Termination: Auditory Cortex (Heschl’s gyrus) BA 41,42 Auditory Cortex Laterality: Bilateral AuditoryAuditory systemsystem

Superior Olivary Nuc

Lateral Lemniscus

Origin: Spiral ganglion Course: CNVIII, auditory pathway, auditory cortex Termination: Auditory Cortex (Heschl’s gyrus) BA 41,42 Laterality: Bilateral SSuperioruperior olivaryolivary complexcomplex →→ soundsound localizationlocalization

MSO = medial superior olive

Purves, et al, Neuroscience, 3rd ed. AuditoryAuditory systemsystem

Lateral Lemniscus Origin: Spiral ganglion Course: CNVIII, auditory pathway, auditory cortex Termination: Auditory Cortex (Heschl’s gyrus) BA 41,42 Laterality: Bilateral AuditoryAuditory systemsystem

Inferior Colliculus

Lateral Lemniscus Origin: Spiral ganglion Course: CNVIII, auditory pathway, auditory cortex Termination: Auditory Cortex (Heschl’s gyrus) BA 41,42 Laterality: Bilateral AuditoryAuditory systemsystem

Brachium of Inferior Colliculus

Origin: Spiral ganglion Course: CNVIII, auditory pathway, auditory cortex Termination: Auditory Cortex (Heschl’s gyrus) BA 41,42 Laterality: Bilateral AuditoryAuditory systemsystem

Medial Geniculate Nucleus

Origin: Spiral ganglion Course: CNVIII, auditory pathway, auditory cortex Termination: Auditory Cortex (Heschl’s gyrus) BA 41,42 Laterality: Bilateral AuditoryAuditory systemsystem –– areaarea A1A1 (A(A --I)I)

Transverse gyri of Heschl CentralCentral auditoryauditory pathwayspathways -- bilateralitybilaterality

Purves, et al, Neuroscience, 3rd ed. AuditoryAuditory systemsystem -- overviewoverview

Modality:Modality: AuditoryAuditory Sensation Sensation (Hearing) (Hearing) Receptor:Receptor: Organ Organ of of Corti Corti of of Cochlear Cochlear Duct Duct CranialCranial Nerve: Nerve: VIII VIII-cochlear-cochlear 1st1st Neuron:Neuron: SpiralSpiral GanglionGanglion 2nd2nd Neuron:Neuron: CochlearCochlear Nucleus,Nucleus, VentralVentral && DorsalDorsal dorsal,dorsal, intermediateintermediate andand ventralventral acousticacoustic striaestriae trapezoidtrapezoid bodybody laterallateral lemniscuslemniscus 3rd3rd Neuron:Neuron: InferiorInferior ColliculusColliculus brachiumbrachium ofof inferiorinferior colliculuscolliculus 4th4th Neuron:Neuron: MedialMedial GeniculateGeniculate NucleusNucleus (MG)(MG) auditoryauditory radiationradiation Termination:Termination: PrimaryPrimary AuditoryAuditory AreaArea (A(A I)I) BrodmannBrodmann areaarea 41,41, 4242 Auditory Pathways

A. spiral ganglion B. dorsal and ventral cochlear nucleus C. inferior colliculus D. medial geniculate nucleus E. Primary auditory area F. superior olivary nucleus G. nucleus of lateral lemniscus 1. acoustic striae & trapezoid body 2. lateral lemniscus 3. brachium of inferior colliculus 4. auditory radiation 5. commissure of inferior colliculus VIIIc. cochlear division AuditoryAuditory pathwayspathways –– 3D3D PrimaryPrimary auditoryauditory cortexcortex –– AA II The Auditory Cortex

Purves, et al, Neuroscience, 3rd ed. TTonotopiconotopic organizationorganization isis maintainedmaintained alongalong thethe entireentire auditoryauditory pathwaypathway TTonotopiconotopic organizationorganization isis maintainedmaintained alongalong thethe entireentire auditoryauditory pathwaypathway

Purves, et al, Neuroscience, 3rd ed. AuditoryAuditory cortexcortex

 TonotopicTonotopic (cochleotopic)(cochleotopic) organizationorganization  BinauralBinaural propertiesproperties ofof corticalcortical neuronsneurons  WernickeWernicke ’’ss area,area, nextnext toto A1,A1, isis forfor thethe comprehensioncomprehension ofof speechspeech  ProbablyProbably asas wewe movemove intointo auditoryauditory associationassociation areasareas -- neuronsneurons thatthat respondrespond toto complexcomplex soundssounds andand speciesspecies --specificspecific vocalizationsvocalizations (Grandma(Grandma ’’ss voicevoice ……)) LesionLesion localizinglocalizing

 BECAUSEBECAUSE OFOF HEAVYHEAVY CALLOSALCALLOSAL CONNECTIONS,CONNECTIONS, AA UNILATERALUNILATERAL LESIONLESION OFOF THETHE AUDITORYAUDITORY CORTEXCORTEX PATHWAYSPATHWAYS DISTALDISTAL TOTO THETHE COCHLEARCOCHLEAR NUCLEINUCLEI WILLWILL RESULTRESULT ININ VIRTUALLYVIRTUALLY NONO LOSSLOSS OFOF HEARINGHEARING  THETHE PATIENTPATIENT WILLWILL MOSTMOST LIKELYLIKELY EXPERIENCEEXPERIENCE ANAN IMPAIRMENTIMPAIRMENT ININ THETHE ABILITYABILITY TOTO LOCALIZELOCALIZE THETHE DIRECTIONDIRECTION ANDAND DISTANCEDISTANCE OFOF SOUNDSSOUNDS SoundSound LocalizationLocalization –– 22 CuesCues

 TimeTime cuescues –– LowLow frequencyfrequency soundssounds (below(below 33 KHz)KHz) areare localizedlocalized duedue toto interauralinteraural timetime differences,differences, capitalizingcapitalizing onon thethe phasephase --lockinglocking abilitiesabilities ofof primaryprimary afferentafferent fibers.fibers. AchievedAchieved byby tthehe medialmedial superiorsuperior oliveolive (MSO).(MSO).  IntensityIntensity cuescues –– HighHigh frequencyfrequency soundssounds (above(above 33 KHz)KHz) areare localizedlocalized duedue toto interauralinteraural intensityintensity differences.differences. TheThe headhead createscreates anan acousticacoustic shadow.shadow. AchievedAchieved byby thethe laterallateral superiorsuperior oliveolive (LSO).(LSO). INTERAURAL TIME DELAY AS A CUE TO THE LOCATION OF SOUND (a) Sound waves coming from the right side reach the right ear first, and there is a large interaural delay before the sound propagates to the left ear. (b) If the sound comes from straight ahead, there is no interaural delay. Delays for three directions are shown.

InterauralInteraural timetime differencesdifferences -- MSOMSO

 IllustrationIllustration ofof howhow thethe MSOMSO computescomputes thethe locationlocation ooff aa soundsound byby interauralinteraural timetime differences.differences. AA givengiven MSOMSO neuronneuron respondsresponds mostmost stronglystrongly whenwhen thethe twotwo inputsinputs arrivearrive simultaneously,simultaneously, asas occursoccurs whenwhen thethe contralatecontralateralral andand ipsilateralipsilateral inputsinputs preciselyprecisely compensatecompensate (via(via ththeireir differentdifferent lengths)lengths) forfor differencesdifferences inin thethe timetime ofof aarrivalrrival ofof aa soundsound atat thethe twotwo .ears. TheyThey systematicsystematic (and(and inverse)inverse) variationvariation inin thethe delaydelay lengthslengths ofof thethe twotwo inputsinputs createscreates aa mapmap ofof soundsound location:location: inin thisthis modelmodel EE wouwouldld bebe mostmost sensitivesensitive toto soundsound locatedlocated toto thethe left,left, andand AA toto soundsound fromfrom thethe right;right; CC wouldwould respondrespond bestbest toto soundssounds comingcoming fromfrom directlydirectly inin frontfront ofof thethe listener.listener. HigherHigher --orderorder corticalcortical auditoryauditory areasareas

“Where” pathway

“What” pathway

“What” & “Where” are processed separately InnerInner earear developmentdevelopment

 TheThe rudimentsrudiments ofof thethe internalinternal earsears appearappear shortlyshortly afterafter thosethose ofof thethe eyeseyes asas twotwo patchespatches ofof thickenedthickened surfacesurface epithelium,epithelium, thethe oticotic placodesplacodes ,, laterallateral toto thethe hindbrainhindbrain

Carnegie stage 12 – ~day 27 LateLate 44 thth –– earlyearly 55 thth weekweek

 By the time the anterior neuropore closes, the first and second pharyngeal arches are evident  The regions between the pharyngeal arches are termed pharyngeal clefts. The indentation just dorsal to the second pharyngeal cleft is the Otic pit developing inner ear, the otic pit.

Otic pit LaterLater earear developmentdevelopment

Carnegie stage 21 – ~day 53

DerivativesDerivatives ofof thethe pharyngealpharyngeal pouchespouches SomeSome ofof thethe neuralneural crestcrest cellscells inin eacheach ofof thethe archesarches becomebecome cartilagecartilage OticOtic vesiclevesicle && pinnapinna developmentdevelopment

CRL External ear development