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 NoisesSound

IntensityNoise Source

60 db Normal conversation, bird song

80 db Heavy traffic, ringing phone

85 – 90 db Motorcycle, snowmobile

90 db Hair dryer, lawn mower

95 – 105 db Hand drill, bulldozer, spray painter

110 db Chain saw

120 db Ambulance siren, rock concert

140 db Jet engine at takeoff

165 db Shotgun 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