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Ch 15b Hearing and Equilibrium Ear anatomy • external ear external acoustic canal tympanic membrane • middle ear 3 ossicles • inner ear • malleus • incus • stapes – – – cochlea hearing vestibule equilibrium semicircular canals equilibrium HEARING cochlea anatomy • • cochlear duct – – fluid filled membrane fluid endolymph receptor Organ of Corti = spiral organ 2 fluid filled chambers : – – – fluid perilymph scala vestibuli contacts oval window scala tympani contact round window Organ of Corti • • • • = spiral organ – receptors for hearing within cochlear duct basilar membrane support hair cells receptor cells – stereocilia extensions into tectorial membrane tectorial membrane covers stereocilia ; stationary Sound • • • sound is a vibration waves of vibrating air (or any medium) physics terms • • • • • frequency # waves per second wavelength distance betw crests amplitude pitch – – – height of each wave different frequency 20 to 20000 Hz 1500 – 4000 Hz most sensitive range low pitch : low frequency ; large wavelength loudness – – hertz (Hz) 0 dB decibels (dB) amplitude lowest audible sound > 120 dB very painful hearing • • GOAL = depolarize the receptor cells – open Na channels How? stretch their hair path of vibration • • • • • • • • air tympanic membrane ossicles oval window perilymph (scala vestibuli) endolymph (cochlear duct) basilar membrane hair cells transmission of sound / vibration • • • • • • • • • • • • • sound wave (air) vibrates tympanic membrane 3 ossicles amplify the vibration stapes vibrates the oval window oval window vibrates perilymph perilymph vibrates endolymph endolymph vibrates basilar membrane basilar membrane vibrates hair cells excitation of receptor cells • • • • • • • • • • • • organ of Corti basilar membrane vibrates hair cells stereocilia stretch against tectorial membrane open K channels K+ (in endolymph) rushes into cell hair cells depolarize hair cells release NT Pitch • • • • • varied thickness of basilar membrane responds to different frequency frequency ~ pitch multiple pitches possible specific areas of auditory cortex auditory processing • • • pitch loudness localization – number of hair cells stimulated where is sound coming from compares both ears • intensity • timing auditory pathway • • • to temporal lobe – – – – – cochlear nerve spiral ganglion cochlear nuclei thalamus temporal lobe to inferior colliculi – auditory reflex to cerebellum – olivary nuclei problems • • • deafness – – conduction deafness neural deafness tinnitus Meniere’s syndrome hearing loss tinnitus vertigo EQUILIBRIUM equilibrium anatomy • • • 2 structures : vestibule semicircular canals static equilibrium (linear) dynamic equilibrium (rotation) receptors • vestibule – – – macula hair cells otoliths • semicircular canals – – – ampula hair cells cupula excitation of macula • • • • position change moves otoliths otoliths bend sterocilia hair cells depolarize only respond to change of position, movement excitation of ampulla • • • rotation moves endolymph endolymph deforms cupula cupula bends sterocilia equilibrium pathway • • • • • hair cells vestibular nerve vestibular nuclei medulla cerebellum reflex movement cerebrum parietal lobe conscious awareness of position and movement problems • • • motion sickness vertigo nystagmus