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 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, otitis media, Meniere’s disease foreign bodies otosclerosis 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 temporal bone
anterior
medial
lateral
posterior BonyBony vsvs membranousmembranous labyrinthlabyrinth
Bony labyrinth Membranous labyrinth SemicircularSemicircular canalscanals SemicircularSemicircular ductsducts
VestibulumVestibulum Sacculus ( anterior cavity ) → cochlear duct 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 cerebrospinal fluid 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 bony labyrinth 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 endolymphatic duct InnerInner earear fluidsfluids
Na + K+ Ca++ Protein mEq/l mEq/l MM g/l Perilymph 140 5 0.68 200 Endolymph 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 Cochlea
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 oval window and ending at the round window. They communicate at the apex of the cochlea via an opening known as the helicotrema . 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 basilar membrane 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 (vestibular membrane) 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 mammals
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 organ of Corti 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 – modiolus SG – spiral ganglion VN – n.vestibulocochlearis FN – facial nerve OC – organ of Corti SV – scala vestibuli ST – scala tympani CD – cochlear duct AO – auditory ossicle А – ampulla of a semicircular canal CA – crista ampullaris 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.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