Hearing Vestibular System 02 25 2014 AUDITORY SYSTEM Ear Anatomy Outer o Pinna o Auditory Canal Middle o Tympanic Membrane o Ossicles malleus stapes incus Differential size of tympanic membrane oval window lead to large magnification of force of sound vibrations 20x bigger amplify energy of vibrations so strong enough when get to cochlea Transduced into fluid environment of cochlea Evolution in Mammals Aquatic inform animals prey nearby b c water is vibrating Inner o Oval window Transduces vibrations from ossicles to cochlea o Cochlea Spiral shape fluid filled increase sensitivity of low frequency vibrations Takes vibrations and transfer to AP Made up of Organ of Corti Tectorial membrane Amplify vibrations for hair cells Gelatinous Otoliths give weight Modified Hair cells Analogous to photoreceptors o About 20k Inner and Outer Vibrate when fluid around them vibrate Inferior to tectorial membrane Innervation IHCs o When vibration tectorial membrane o Protein bridges between tall and Upon bend rip open lid on K bends hair cells short cells channels Allow depolarization Ca enters Vesicles release contents Leads to signal propagation down auditory nerve o Can fire spontaneously i e hear something when lay in bed Especially when not very active If too loud stereocilia fall down and break cannot recover o Over lifetime lose majority of frequencies between 10 000kHz 20 000kHz Basilar membrane Stiff o Wide apex to narrow base Varies in width thickness o Gives ability to hear many different frequencies o One region in particular vibrates more than rest specific frequency o Very high frequencies are transduced into complex patterns of APs out of cochlea o Range roughly 500Hz 16kHz Bends upon vibration key for audition Tonotopically organized Auditory nerve Brings info back to brain stem Pathway o Cochlear nuclei Very organized specific spots frequencies o Superior olivary nuclei tell brain which ear heard it first determine by difference in arrival at given spot for certain freq o Inferior coliculus Organize fast orienting response to loud sounds Controls sound reflex o Medial geniculate nucleus thalamus Process auditory sensation Gets info from both ears bilateral o Auditory Cortex Tonotopic organization in AI areas 41 and 42 Primary and Secondary specific areas responsible for specific frequency still separation from each other Info goes to both hemispheres o Injury to one side of brain does not procude deafness on that side of the brain VESTIBULAR SYSTEM Cochlea o Semicircular canals 3 Organized in x y z planes roughly Tell if upright or laying down or accelerating Fluid has inertia as head turns quickly and bends stereocilia causes bend of stereocilia If move receives signal that you have moved Continuous movement causes fluid to catch up and start moving Feel like not spinning even shortly after sudden stop even if room is Can use eyes to overwhelm signals of semicircular canals to prevent dizziness from spinning Dancers and ice skaters spin head quick and focus on one point If ever disconnect b t signals of eyes and semicircular canals result nausea Consumption of alcohol less stable than fluid in ear cause unusual asymmetrical movements in semicircular canals I e canal says moving eyes say standing still other canal spinning Nystagmus occur in eyes b c weird signals Basis for eye hand coordination test for DUI
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