Chapter 2 Vestibulocochlear OrganThe vestibulocochlear organ (Fig. IV-2-1) istemalearTheextermalandmiddleearsarethesoundcomposed of the auditory apparatus and vestibularolltingdtramingaparahialapparatus.Both organs buried in the temporal boneissuchanorganthatcanreceivethestimuliofbothare closely associated anatomically. It consists ofsound waves and changes of the position and move.three parts: theexternal ear, the middleear and the in-ment of the head.AuricleBony semicircular canalsVestibuleCochleaVestibulocochlearnFacialnTensortympaniBonypartofextemalacousticmeatusIntermal carotidaCartilaginous partofextermalacousticmeatusAuditory tubeCartilage ofauditory tubePharynxIntermal jugular v.TympanicmemFig. IV-2-1 The vestibulocochlear organexternal ear.It consists ofa single elastic cartilageSection1 Externalcovered with thin skin contains hairs, sweat glandsand sebaceous glands (Fig. IV-2-1, 2).The auricularEarlobule (earlobe)liesbelow theauricle,and consistsThe external ear consists ofthe auricle,externaloffibrous,adiposetissues and blood vessels.acousticmeatus andtympanicmembraneThe anterolateralsurfaceoftheauricleis iregularconcave, but its posteromedial surface presents con-vexThextenalacousticpore,rests inthefossaoI.Auriclethe anterolateral surface ofthe auricle,and leadstotheexternal acoustic meatus.The auricle or pinna is the shell like part of the·266扫描全能王创建
Chapter2 Vestibulocochlear Organ · 267 .HelixTriangular fossaCrura of antihelixCymba of auricular conchaCrus of helixAntihelixCavity of auricularconchaTragusAntitragusIntertragicAuricular lobuleFig, IV-2-2 The auriclesmeatus.II.External Acoustic Me-III .Tympanic MembraneatusThe tympanic membrane or eardrum is thin, semi-The external acoustic meatus or external auditorytransparent,and almostoval.It separates thetympan-canal extends from the external acoustic pore to theic cavity from the external acoustic meatus (Fig.IV-2-tympanicmembrane(Fig.IV-2-1).Itis approximate-1,3).Itis placedobliquelyforming an angle of45ly2.5cminlengthandhastwo structurallydifferentto55 degrees with the floor of the meatus, so that itsparts, the outer one third cartilaginous part and thelateral surfacefacesbothforward anddownward.inner two thirds osseous part.It is narrowed at theThe tympanic membrane is a connective tissuejunction of its osseous and cartilaginous parts.Be-membrane and composed of three layers:an outercause oftheobliquity of tympanic membrane,thecuticular layer, an intermediate fibrous layer and anwalls are not of the same length.Itforms an S-shapedinner mucous layer.The cuticular layer is continuouscurve,dircted atfirst medially,anteriorly and slighwith the skin of the external acoustic meatus andlyup,then posteromedially and up,and lastly againhairless.The fibrous layer is covered on its outer cu-anteromedially and slightly down.The best view ofticular layer and on its internal surface by the mucousthe tympanic membrane is obtained if the auricle ismembrane of thetympanic cavity.It has an externalgently drawn upward and backward. The examinerlayer of radiating fibres diverging from thehandleofshould remember that the external meatus of a childthe malleus and a deep layer of circular fibres.Theis very short.mucous layer is lined with the mucous membrane ofThe external acoustic meatus is lined by a layerthetympanic cavity.fthinskinwhichalsocoverstheoutersurfaceoftheIts thickened margin of the membrane,thefibro-tympanicmembraneBeneaththesknliethewaxsecartilaginous ring,is inserted into thetympanic sulcuscretingerumnousglanwhhscretinghuat the medial end of the external acoustic meatus. Itmarwahkinoauithnandihastwo folds,the anteriorandposteriormalleolarsuutanustsuisscarcbutrcsenoryerfolds intheupperendofthetympanicmembrane,andthey are prolonged to the lateral process of the malle-boy pars omau,oreurifmmus.Above these twofolds,the small part of the mem-ondiio,thaietfsexrme pin扫描全能王创建
·268.PARTIVSENSORYORGANSthat isthetense panhefacidpartfthympanicbraneislax and thin,socalledthefaccid part,whilemembrane is devoid ofthefibrous layer.the remainder of the membrane is tightly stretched,Body of incusHeadofmalleusPosteriormalleolarfoldFlaccidpartMalleolarprominenceAnteriormalleolarfoldMalleolar strigFibrocartiliaginous ringUmbooftympanicmembraneTensepatConeof lightFig.IV-2-3 The tympanic membraneIn life the tympanic membrane is pearlygray.Thewall of the inner ear. It is a rather large cavity in thehandle of the malleus is firmly attached to the innertemporal bone.It is the main part of themiddle earsurface of the tympanic membrane as far as its center,its capacity is about 1-2 cm.There are auditory ossi-and its lower end lies opposite the point ofmaximumcles,ligaments,muscles,vessels and nerves inside theindrawingof themembrane,theumbo,formed bythetympanic cavity.The tympanic cavity is connectedtraction of the lower end of the handle of malleus.anteriorly with the nasopharynx by the auditory tube,Remember that the appearance of the malleus is seenand posteriorly with the mastoid cellsby the mastoidthrough the membrane and that the membrane is con-antrum.cave when viewed from this aspect.This concavityproduces a bright area, the cone of light, can be seenWalls of the tympanic cavityanteroinferiortotheumbo.Section 2 Middle EarThe tympanic cavity is shaped like a narrow, sixsided box (Fig. IV-2-1, 4, 5). It possesses six walls:The middle ear (Fig.IV-2-1) lies between the exter-1) Roof or tegmental wall is a thin plate ofnal ear and internal ear,and it includes:the tympaniccompact bone, called the tegmen tympani whichcavity,the auditory tube,the mastoid antrum and theseparates the middle cranial fossa from the tympanicmastoid air cells.cavity. In youth, the unossifed suture ofthe superiorwall may allow the infection to spread from the tymI.Tympanic Cavitypanic cavity intothe cranial cavity directly and foman intracranial abscess.In adults, veins from the tympanic cavity traverse this suture to the superior sinusThe tympanic cavity is an irregular air filledand may alsotransmit infection tothese structures.spacebetween thetympanic membrane and the lateral扫描全能王创建
Chapter2VestibulocochlearOrgan ·269.IncusEntranceofmastoidantrum.Mastoid antrurmTegmentympanMastoidcellsMalleusStapeTympanicmemtStapedius.TensortympaniMastoidcellsAuditory tubeFacialnTubeof internaljugularaugularfosssFig.IV-2-4Thelateral walloftympanic cavityProminence of lateral semicircular ductMastoidantrumProminence offacial canalFenestravestibuliAuditory tubeMastoidcellsInternal carotidaPyramidaleminencPromontoryFenestracochleaeInternal jugular aIntemal jugular v.Facial nStyloid processMastoidprocessFig. IV-2-5 The medial wall of tympanic cavitywall aretwoparallel canals extendingtothetympanic2) Floor or jugular wall is narrower and thick-er than the tegmental wall. It separates the tympaniccavity.The upper and smaller is the smaller semicanalcavity from the jugular fossa. The bone of this wallfor tensor tympani; the lower and larger is a largersemicanal for auditory tube, the bony part of the audi-may be patchily deficient, so the tympanic cavitytory tube.is separated only from the jugular vein by mucous4)Posterior ormastoid wall is absent superi-membrane and fibrous tissue. This may cause theorly where the aditusto the mastoid antrum leaves thebeginning part of the jugular vein toproject intotheepitympanic recess.The pyramidal eminence is justtympanic cavity.below the opening of mastoid antrum and behind the3) Anterior or carotid wall is close to the in-fenestra vestibuli. It contains the stapedius.ternal carotid artery.Opening aboveon the anterior扫描全能王创建
·270·PARTIVSENSORYORGANSparalysis.5) Medial or labyrinthine wall is also the lat-6) Lateral or membranous wall consists al.eral boundaryof theinnerear.Aroundedelevationmost entirely of the tympanic membrane. Superiorlyonthemiddleofthiswall isnamedthepromontoryit isformed by the lateral wallof theepitympanicformed by the large first turn of the cochlea.The me-recess.Thehandleofthemalleus is incorporated indial wall has two small windows.Thefenestra ves-thetympanic membraneand its head extends intothetibuli or oval window is a reniform opening postero-epitympanic recess.superiorto thepromontory,and filled bythebaseofthe stapes and annular ligament. The fenestra cochleaAuditory ossiclesorround window lies posteroinferiortothetympanicpromontory,inferior to thefenestra vestibule,and isclosedbythe secondarytympanicmembraneinvivo.The three auditory ossicles, the malleus, incusInthe epitympanicrecess,abovethefenestravesti-and stapes,form ajointed arch between thetympanicbule,is an ill-defined,horizontal ridge produced bymembrane and the fenestra vestibule.the bone covering the canal for the facial nerve.TheLaterally,the handleofmalleus is attached to theprominence of facial canal is extends back and downtympanic membrane,andmedially,the base of thto the posterior wall of thetympanic cavity.Understapes is fixed to the margins of the fenestra vestibuli,inflammatoryconditionofthetympaniccavity,thefa-while the intermediate incus lies between the malleuscial canal may be involved, which may lead to facialand the stapes (Fig.IV-2-6).IncufeoEpitympanic recessBody of incusMalleusShort crusHeadofmalleutapesLongcrusHead of stapesExtemalacousticmeatuPosteriorcrusTympaniccavity ManubriumofTympanicmembr-BaseofstapesmalleusAnteranFig.IV-2-6The auditory ossiclesThe chain of ossicles transfers sound waves fromthe stapedius contract simultaneously. While the ten-the handle of themalleus to the incus and stapes,sortympani contracts, it pulls thehandle of the malle-transmitting the vibration to the inner ear.us medially,tenses the tympanic membrane,and thusreduces the amplitude of vibration.On the stapedius3. Muscles of the tympanic cavitycontraction, it pulls the neck ofthe stapes posteriorly,tilts the base in the fenestra vestibule tightening theThere are two muscles, the tensor tympani andannular ligament and reducing the pressure of soundstapedius, in each side of the tympanic cavity.Thewavefor the inner ear.tensor tympani arises from the semicanal for tensortympani and ends the handle of malleus. The stape-II.Auditory Tubedius arises from the pyramidal eminence of posteriorwall of the tympanic cavity and is inserted into theThe auditory tube, also named eustachian tube,neckofthestapes.Commonly,thetensortympaniand扫描全能王创建
Chapter 2Vestibulocochlear Organ ·271 -during childhood. The mastoid antrum and mastoidconnectsthetympaniccavitytothenasal partofthepharynx, allowing airtoenterorleave the cavity itair cells are lined by mucous membrane of the tym-panic cavity.The infection in the middle ear, namedbalances the pressure on both sides of the tympanicotitismediamayspread intothemastoidantrumandmembrane and so allows it to vibrate freely.The tube is about 35-40mm in length, and isthe mastoid air cells.formed partly by bone and partly by cartilage andSection 3Internal Earfibrous tissue.The junctionofthese twoparts is nar.rowest, termed the isthmus (Fig. IV-2-1).The internal ear (Fig.IV-2-7,8) is medial to theThe bony part, about 12 mm in length, starts frommiddleear,buried within thehard petrous part of thetheanteriortympanicwall,passesforward,downwardtemporal bone.It consists of two parts:the bony lab-and inward, then gradually narrows to isthmus. Theyrinth and the membranous labyrinth.The membra-cartilaginous part, about two thirds of the auditorynous labyrinth is filled with a fluid called endolymph.tube, opens into the nasopharynx, forming a tubalelThe membranous and bony labyrinths are separatedevation behind the pharyngeal orifice.The auditoryby a space containing a fluid called perilymph.Thetube is lined by mucous membrane that continuousendolymph does not communicatewith perilymph.posteriorly with that of the nasopharynx.The internal ear is concerned with the reception ofThe pharyngeal orifice and the cartilaginous partsound and the maintenance of balance.remains closed except during swallowing or yawning. When the cartilaginous part of the auditory tubeopens, it prevents excessive pressure in the tympaniccavityThe auditory tube forms a route through whichinfections may pass from the nasopharynx to thetympanic cavity. The auditory tube is easy to beblocked by swelling of itsmucousmembrane.Whenit is blocked, the residual air in the tympanic cavityis absorbed.This results in lowering of pressure inthe tympanic cavity and the retraction of the tympan-ic membrane.Underthese circumstances fluid mayexude into the tympanic cavity.You might test thismechanism when you are ascending or descending inThe position of internal ear in the skullFig.IV-2-7an airplane start chewing gum to increase your swal-lowing and observe whether this relieves the discom-I.Bony Labyrinthfort in yourears.At youth the auditory tube is about half its adultlength, its direction being more horizontal and itsThe bony labyrinth is a series of intercommuni-bony part relatively shorter but much wider. So thecating cavities in the compact bone of petrous part ofinfammation of the pharynx may easily spread alongthetemporal bone,which is lined by periosteum.Thethe auditory tube into thetympanic cavity and causesbony labyrinth is divided into three parts:thecochlea,the vestibule and the bony semicircular canal (Fig.IVthe otitis media.2-9).They aredifferent in shape,but communicatewith each other. II . Mastoid antrum and AirCellsVestibuleThe mastoid antrum is an airflled spaces contin-The vestibule is the central part of the osseousuous anteriorlywiththeepitympanicrecessthroughlabyrinth and lies medial to the tympanic cavity.thaditusFig4)MastoidaircllsseresSomewhat ovoid in shapebuttransversely narrow,itineommunicatingaviiehatfmflledmeasures4-5mm inlength,and transversely3mm.Itstensionsotheantrumasthemastoidprocessgrows扫描全能王创建
·272·PARTVSENSORYORGANSlabyrinth isathin,pforatedplateofbone whichlateral wall (namely themedial wallof the tympanicparatestheesibumthdhinemalcavity),pierced by the fenestra vestibuli communi-acousticmeaus, throughthsplatepasstheriphcating with the tympanic cavity,which is closed byeral branches of the vestibulocochlear nerve into thethe base of the stapes with its annular ligament inmembranous labyrinth.vivo.The fenestra cochleae is closed by the second-arytympanic membrane.The medial wall of bonyAnterior semicircular ductLateral membranous ampullaPosterior semicircularducAnteriormembranousampullaCupula of cochleaUtricleLateralsemicircular ductCochlearductSacculeSimple bony crusEndolymphaticductUtriculosaccular ductEndolymphatic sacFenestra vestibuliDuctusreuniensPosteriormembranous ampullaFenestra cochleacFig.IV-2-8The internal earAnteriorbonyampullaAnteriorsemicircular canalLateral bony ampullaCommonbonycrusCochleaFenestravestibuliLateral semicircular canalPosterior semicircular canalSimplebony crusPosterior bony ampullaSemicircular canalVestibuleCochleaFig.IV-2-9Thebony labyrinthThere are five openings of the semicircular canalswallof the vestibule, a large opening interconectson the posterior wall of the vestibule. On the anteriorwith the scala vestibuli of the cochlea.扫描全能王创建
Chapter2 Vestibulocochlear Organ ·273 .shelfofbone, the osseous spiral lamina,protrudesfrom the modiolus like the thread on a screw.This2.Cochleastarts at the vestibule and continues to the apex. Thisreaches about halfway across the cochlear canal,partly dividing it into an upper scala vestibuli and aThe Cochlea which is shell like part of the bonylower scala tympani with thebasilarmembrane of thelabyrinth contains the part of the internal ear that iscochlear duct (Fig. IV-2-10).The scala vestibuli andconcerned with hearing, the membranous cochleathe scala tympani pass to the fenestra vestibuli and fe-or cochlear duct, The bony spiral canal surroundsnstracochlearespectivelyand insidethemareflledand forms the central pillar for a spiral tube of21/2-with perilymph.The width of lamina of modiolus2 3/4 turns arranged in the form of a short cone. Thegradually decreases from the basal to the apical coilcochlea is placed anterior to the vestibule. The apexofthe cochlea,andnearthe summitof the cochleaor cupula points anterolateraly, its widest basal coilthe lamina ends in a hook shaped process, called thepoints posteromedially towards thefundus ofthe inhamulus of spiral lamina.The hamulus and the mo-ternal acousticmeatus.diolus form thehelicotrema,through which the scalaThe modiolus is the conical osseous central pillarvestibuli and scala tympani communicate with eachofthe cochlea, in which there are canalsforthe bloodvessels and nerves. It is about 3 mm long.A smallother.Cupula of cochleaSpiral organScala vestibuliVestibularwall ofcochlearductCochlearductOsseous spirallaminaModiolusCochlear ganglionTympanicwall ofcochlear ductScala tympaniFig. IV-2-10 The section of cochleapetrous part of the temporal bone, lying under theanterior surface ofits arcuate eminence.The posterior3.Bony semicircular canalssemicircular canal,also vertical,curves backwards al-most parallel with the posterior surface ofthe petrousThe Bony Semicircular canals are three in num-bone.The horizontal or lateral semicircular canalber: superior (anterior)posterior and horizontaldirected horizontally and posterolaterally.Each canal(lateral) semicircular canals.They lie posterosuperiorhas two bony crura, one of which is dilated, namedto the vestibule and are compressed from side to side.the ampullary bony crus; the other two crura of an-Each of them describes about two thirds of a circle.terior and posterior canals form one common bonycrus, open together into the vestibule, while the an-(Fig.IV-2-9)The superior or anterior semicircular canal isothersimplebonycrus ofthelateral canal opens intovertical and planed transverseto thelong axisofthethe vestibule separately.扫描全能王创建
·274·PARTIV SENSORYORGANSated in its walls.II.Membranous LabyrinthThe membranous labyrinth includes: the utricleand saccule, two small sacs occupying the vestibule,@ thecochlear duct, in the osseous cochlea, threeThe membranous labyrinth is a series of intercom-membranous semicircular ducts in the semicircularmunicating membranous canals and sacs with a fluidcanals.The various parts ofthe membranous labyrinthcalled endolymph, lying within the bony labyrinthform a closed system of communicating channels.(Fig.IV-2-8, 11).It is similar to bony labyrinth inThe membranous labyrinth is lined with epithelumshape.The spiral organ and vestibular organs are situ-andcontainsendolymphinsideCerebralduramaterEndolymphatic sacBony semicircularcanabarachnoidspaceVestibuleCochlear aqueductUtricleEndolymphatic ductSemicircular ductSacculeAmpulla-CochlearductFenestravestibuliScalatympaniAuditory ossiclesTympanic membrScala vestibuliFenestra cochleacAuditorytubeFig. IV-2-11 The membranous labyrinthlinear movements on acceleration or deceleration ofthe head.Utricle and sacculeOn the posterior wall of the utricle there are fiveopenings of the membranous semicircular ducts. TheThe utricle and saccule have membranous wallssmall utriculosaccular duct communicates with theand are suspended within the vestibule. The utricle,utricle and the saccule, which also joins the endo-the larger of the vestibular sacs, is irregularly oblonglymphatic duct.The endolymphatic duct traverses theand occupies theposterosuperior part of the bonyvestibular aqueduct and ends as ablind dilatation, thevestibule. The saccule is an oval vesicle and lies inendolymphatic sac.the anteroinferior part of the vestibule and its lowerend communicates with the cochlearduct through theductus reunions. (Fig.V-2-11)2. Cochlear ductThe macula utriculi is a pale, oval thickening ofthe floor and adjacent anterior wall of the anterior partThe cochlear duct is a spiral, blind tube, extend-of the utricle.The macula sacculi lies on the anterioring from the vestibule to the summit of the cochlea,wall of saccule. The maculae are the organs of stat-which is firmly fixed to the internal and externalic balance.They may be stimulated not only by thewallsofthe cochlearcanal withinthebony labyrinthchanges of the position of the head, but also by the(Fig.IV-2-12)扫描全能王创建
Chapter 2 Vestibulocochlear Organ·275.VestibularmembranCochlear ductArteryScalavestibuliStria vascularisSpiralspiralmembraneorganCochlear ganglionScala tympaniFig.IV-2-12The section of bony spiral canalIt is triangular in transverse section and lies be-tween the osseus spiral lamina and the external wallSemicircular ducts3.of the cochlear canal. The cochlear spiral canal is di-yided bythevestibularmembrane into three separatedThe semicircular ducts are oval in transverse sec-channels, namely the scala tympani, scala vestibulition,and are attached to one wall of themuch largerand cochlear duct.The cochlearduct has three wallssemicircular canal in which they lie. But they are ap-(Fig.IV-2-9).Its roofor superior wall is the vestibularproximately one third of the diameter of them (Fig.IV-membrane that separates the cochlearduct from the2-8).The semicircular ducts also are three in number.scala vestibuli;its lateral wall termed external wall ofIn the bony ampulla, each ducts is dilated and almostcochlearductisformedbythethickenedendosteumfills the space available,forming an membrane am-lining thebonycanal of the cochlea and is concernedpulla. There are the ampullary crests on the wall ofwith theproduction of the endolymph, its floor,infe-membranous ampullae.The semicircular ducts openriorwall isformed bythebasilaror spiral membraneinto the utricle byfive orifices, one being common toand the outer part of the osseous spiral lamina, andthe medial end of the anterior and the superior end ofseparates the cochlear duct from the scala tympani.the posterior duct.The cochlear duct is a blind tube, which ends superi-The ampullary crests are the organs of kineticorly at the apex of the cochlea. The lower end of thebalance,and respond to rotational acceleration oftheduct, through the ductus reunions, communicates withhead.the saccule.The spiral organ,also called organ of Corti, conIl.Internal Acoustic Meatussists of several elements formed from the thickenedepithelium of the cochlear duct on the basilar lamina.The internal acoustic meatus (Fig.IV-2-1) is aThe more central of these structures are two rows ofcells, the internal and external rod cells (of Corti) ornarrow canal running laterallyfor about Icm withinpllar cells. It is the receptor for auditory sensationthepetrous part of the temporal bone.Theopening ofthe meatus, internal acoustic pore, is on the center ofand consists of a number of hair and support cells.the posterior surface of the petrous part.The internalThis complex sensory organ developed from the epi-acousticmeatus is closed laterallybya thin,perforatthelium of the cochlear duct (Fig IV-2-12) .The scala tympani separated from the scala ves-ed plate of bone which separates it from the internalear.Through the fundus of plate thefacial, the vestib-tibulibytheochlearduct,andonlyattheapexothulocochlearnerves and vessels of the labyrinth entercochleatheswoscalacommunicatewitheachothor leave the internal ear.through the helicotrema.扫描全能王创建