April 17, 2012
pinna to ear drum
filled with air
ear drum to oval window(cochlea)
filed with air
cochlea (oval window to auditory nerves)
filled with fluid
channel sound wave (variations in air pressure) to ear drum
vibrate in resonance with sound wave to drive the ossicles
Equalize pressure on both sides of eardrum
d)
hammer anvil and stirrup – malleus, incus, and stapes
vibrate the oval window causing fluid in cochlea to vibrate
e)
vibration of cochlear fluid causes hairs (cilia) to vibrate which creates electrical impulse
different hairs resonate with different frequencies
transform vibrations of fluid into electrical impulses
f)
send electrical impulses to brain to allow sound to be interpreted
April 17, 2012
Longitudinal, mechanical wave – variations in pressure (eg. Air)
Produced by vibration of object producing sound
Frequency of sound is frequency of object’s vibration – forced oscillation – driving
frequency
force per unit area
\
mechanical advantage that turns a small force at tympanic membrane
into a larger force at oval window (1.5:1) – force multiplier
small area of eardrum and smaller area of oval window (20:1)
Lever action of ossicles increases force which then acts on a smaller area
Sound pressure is amplified by inner ear
PO > P T since F increases and A decreases
(30:1)
Transmission not reflection
Mechanism for pressure transformation between media of different densities (air and fluid)
Without it, most sound would be reflected from cochlear fluid rather transmitted – when densities
are very different at a boundary (impedance matching)