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Ch 9 Hearing.doc

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PSYC 280
John Reynolds

Ch 9 Hearing Vestibular perception taste and smellHearing our auditory system detects rapid changes of sound intensity in dB and frequency in HzEar parts and their functionsOuter parts of the auditory system have been shaped through evolution to capture biologically important sound vibrations and direct them into the inner parts of the ear where mechanical force of sound is transduced convert energy into neural activityExternal ear pinnae funnel sound waves into the second part of the external ear ear canalPinna is distinctly mammalian characteristics animals move ears to help find the source of soundReceptorsmuscles in pinnae give info to auditory path of the position of external ears to help find soundhills of the pinna can modify the sound can be enhancedsuppressedeg shape of human ear can increase sounds bw 20005000 Hzshape of external ear is also imp for finding the direction and distance of the soundmiddle ear concentrates on sound energiesmade up of membrane muscle bonetiny microphone auditory canalneural receptor cells of inner earmiddle ear consists of taut tympanic membrane eardrum sealing the end of the auditory canal and chain of tiny bonesossicles that mechanically couple the tympanic membrane to the inner ear at the oval window opening from middleinner earthese ossiclestiny bones malleus incus stapessound waves in the air strikes tympanic membrane causing vibration the same frequency as the soundmovement of tympanic membrane moves the chain of ossicles amplifies sound pressure to allow production of movement in fluid of inner ear2 muscles control the linkage bw the ossicles to improve auditory and protect inner ear from loud noise tensor tympani attached to malleus connected to tympanic membrane and stapedius attached to stapeswhen sound arrives brain signals muscles to contract stiffen ossicles and reduce effectiveness of soundmiddleear muscles also modify selfmade soundswithout this body will be distractingly loudmiddle ear muscles activate just before we produce selfmade sounds like speechcoughingCochlea converts vibrational energy into waves of fluidInner ear where sound converts into neural activityCochlea in temporal bone snail 3 panelsScala vestibuli vestibular canalScala media middle canalScala tympani tympanic canalOval window is under the cochlea movement of fluid inside cochlea in response to push on oval window makes a second window round windowseparate scala tympani from middle ear to bulge outwardOrgan of Corti important component to convert sound into neural activity 3 structuresHair cells sensoryreceptor cells transducer movements of basilar membrane into electric cellsSupporting cellsBasilar membrane base of organ separates scala tympani from scala media and vibrates from soundstapes moves into sound waves hitting eardrumwaves in scala vestibuliwaves in basilar membranehigh frequencies at base membrane is narrow low frequency at apex membrane is wide2 sets of hair cells within organ of Corti inner hair cells IHC and outer hair cells OHC in 3 rowsEach hair cell has stereociliaciliaAtop the organ of Corti tectorial membraneAuditory nerve fibers touch the base of hair cellsOrgan of Corti has 4 synapses and nerve fibersAfferents release messages from hair cells to brain comes from IHCgive rise to perception of soundEfferents release messages from brain to hair cellsFew nerve fibers contact OHC mutant mice that lack IHCdeafOHC cant detect sound pushes tectorial membrane in response to commands from brain w efferent nerve fibersIHC receive efferent messages transduce sound into neural activitySoundsvibrations of basilar membrane vibrations bend hair cell cilia in tectorial membraneSmall displacements of hair bundles cause changes in ionic channels of sterocilia Tip links tips of sterocilia role in generation of hair cell potentials Sounds cause sterocilia to sway increase tension on elastic tip linksopen ion channelsIf hair sway back ion channel snap shut ion channel contain protein TRPA12Opening ion channels allow in rush of K and Cadepolarization
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