Still Chapter 17 Hearing & Balance

HEARING 3 main parts of the ear: Outer Ear Middle Ear Inner Ear

Outer Ear Pinna = outside portion of the ear, focuses sound waves on the eardrum (tympanic membrane) External auditory canal = ear canal, leads to the eardrum, contains ceruminous glands that secrete earwax

The eardrum separates the outer and middle ear

Middle Ear Sound vibrations from the eardrum pass to auditory ossicles (three tiny bones – malleus/hammer, incus/anvil, & stapes/stirrup) which transmit sound to the inner ear Eustachian tube connects to pharynx, allowing air pressure to equalize on both side of the eardrum; can be blocked by infections

The Inner Ear Cochlea filled with fluid picks up vibrations from middle ear which cause hair cells in cochlea to bend Movement of hair converts vibrational energy into nerve impulses

Auditory Pathway Vestibulocochlear nerve VIII takes the information to medulla oblongata and then to auditory cortex in the temporal lobe

Sound Levels of Common Noises Sound Intensity Noise Source 60 dbNormal conversation, bird song 80 dbHeavy traffic, ringing phone 85 – 90 dbMotorcycle, snowmobile 90 dbHair dryer, lawn mower 95 – 105 dbHand drill, bulldozer, spray painter 110 dbChain saw 120 dbAmbulance siren, rock concert 140 dbJet engine at takeoff 165 dbShotgun blast Safe range Risk range Injury range

BALANCE & COORDINATION

Semicircular Canal in Inner Ear Maintain balance and equilibrium Filled with fluid and hair cells When you tilt your head, fluid and hair move and stimulate nerve cells to carry info to cerebellum