Hockenbury Discovering Psychology 5th txtbk

Hearing103the stirrup, transmits the amplified vibration to the oval window. If the tiny bonesof the middle ear are damaged or become brittle, as they sometimes do in old age,conduction deafness may result. Conduction deafness can be helped by a hearingaid, which amplifies sounds.Like the eardrum, the oval window is a membrane, but it is many times smallerthan the eardrum. The oval window separates the middle ear from the inner ear.As the oval window vibrates, the vibration is next relayed to an inner structure calledthe cochlea, a fluid-filled tube that’s coiled in a spiral. The word cochlea comesfrom the Greek word for “snail,” and the spiral shape of the cochlea does resemblea snail’s shell. Although the cochlea is a very complex structure, it is quite tiny—nolarger than a pea.As the fluid in the cochlea ripples, the vibration in turn is transmitted to thebasilar membrane, which runs the length of the coiled cochlea. Embedded inthe basilar membrane are the sensory receptors for sound, called hair cells,which have tiny, projecting fibers that look like hairs. Damage to the hair cellsor auditory nerve can result in nerve deafness, which cannot be helped by a hearingaid. Exposure to loud noise can cause nerve deafness (see Table 3.2 on thenext page).inner earThe part of the ear where sound is transducedinto neural impulses; consists of thecochlea and semicircular canals.cochlea(COCK-lee-uh) The coiled, fluid-filled innerearstructure that contains the basilar membraneand hair cells.basilar membrane(BAZ-uh-ler or BAZE-uh-ler) The membranewithin the cochlea of the ear that containsthe hair cells.hair cellsThe hairlike sensory receptors for sound,which are embedded in the basilar membraneof the cochlea.Sound waves arecollected in theouter ear.Sound waves areamplified in themiddle ear.Sound waves are transformedinto coded neural messagesin the inner ear.AnvilHammerSemicircular canalsOval window Auditory nerveTo thalamus andprimary auditorycortex of brainSoundwavesPinnaEar canalStirrupEardrum(a)Major Structures of the EarOuter ear Middle ear Inner earAnvilCochlea, partially uncoiledHammerStirrupSound waveCochleaFigure 3.8 The Path of Sound Through theHuman Ear The path that sound waves takethrough the major structures of the humanOuterearearis shown in (a). After being caught by theouter ear, sound waves are funneled downthe ear Hamme canal to the eardrum, which transfersthe vibrations to the structures of the middleear. In the middle ear, the vibrations are amplifiedand transferred in turn to the ovalwindow and on to the fluid-filled cochlea inthe inner ear (b). As the fluid in the cochleavibrates, the basilar membrane ripples, bendingthe hair cells, which appear as rows ofyellow tips in the top right section of thecolor-enhanced scanning electro micrograph(c). The bending of the hair cells stimulatesthe auditory nerve, which ultimately transmitsthe neural messages to the auditory cortexin the brain.SoundwavesFluidEar canalEardrum(b)Detail of CochleaHaircellsBasilarmembraneVibrations influid causethe basilarmembrane towave up anddown.(c)