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PHYS 215 (11)
Lecture 11

PHYS 215 Lecture 11: Hearing

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Ball State University
PHYS 215
Kelly Worden

1. Hearing  External, middle, and inner ear o External and middle ear  Transmit sound waves to the fluid-filled inner ears o Inner ear the cochlea  Receptors that convert sound waves into nerve impulse o Vestibular apparatus of the inner ear  Sense of equilibrium o Each inner ear region has mechanoreceptors  Cochlea (inner ear) o Basilar membrane – separates the Scala tympani from the Scala media o Organ of Corti – sits on the basilar membrane and contains the auditory receptor neurons o Tectorial membrane – lies above the organ of Corti o Perilymph – fluid in the Scala vestibule and Scala tympani (similar to CSF, low K+, high Na+) o Endolymph – fluid in the Scala media (similar to ICF, high K+ and low Na+)  How do we hear? o Sound waves that reach the ear into the external auditory canal o Waves strike the tympanic membrane causing the membrane to vibrate o Vibrates slowly in response to low-frequency sounds and rapidly in response to high-frequency sounds o Central area of tympanic membrane is connected to the malleus, which also starts to vibrate. Vibration is then picked up by the incus which transmits the vibration to the stapes o Stapes moves back and forth and pushes the oval window in and out  Middle ear bones conduct a signal (vibrations) from the tympanic membrane to the inner ear o Middle ear amplifies tympanic movements and transmits them to the oval window o Movement of the oval window produces waves that travel through the fluid in the cochlea o Cochlea contains the organ of Corti, sense organ for hearing  Sound waves o Consist of alternating regions of compression and refraction of air molecules o Pitch  Depends on the frequency of air waves  Region of the basilar membrane that vibrates o Loudness  Depends on the amplitude of air waves o Timbre  Determined by overtones  Waves in the cochlea o These waves have the same frequency as the sound waves in the air o Different frequencies of eaves disturb different parts of basilar membrane in the cochlea o Hair cells are mounted on the basi
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