Lecture 17 - Functional Ear Anatomy Flashcards
Outer ear
pinna and auditory canal
pinna
help with sound location and some amplification
differs across individuals
auditory canal
tube-like 3 cm long structure
filled with wax and hair: protective function
It protects the tympanic membrane (eardrum) at the end
of the canal.
• The resonant frequency of the canal amplifies frequencies
between 1,000 and 5,000 Hz. (Excellent for voices.) = why we’re so sensitive to those frequencies !!
middle ear
Two cubic centimeter cavity separating inner from outer ear
tympanic membrane, ossicles
tympanic membrane
(eardrum) responds to pressure waves in the air.
There is air pressure on both sides of the membrane.
• Motion of the eardrum will drive the ossicles of the middle ear.
the three ossicles
take the mechanical vibration (air molecules against the eardrum) and use it to drive the oval window in the inner ear
malleus, incus, stapes
malleus
moves first
moves eveytime the eardrum vibrates
incus
transmits and amplifies vibration
stapes
transmits and also amplifies signal onto oval windo
changing transmission mediums
Outer and middle ear are filled with air.
• Inner ear is filled with fluid that is much denser than air.
• Pressure changes in air transmit poorly into the denser medium.
– Less than 1% of the vibrations can transmit directly.
• Ossicles act to amplify the vibration for better transmission to the fluid.
– Can do this up to a factor of 50.
Middle ear muscles
can dampen the ossicles’ vibrations to protect the inner ear from potentially damaging stimuli.
Stapes is pulled away from the oval window to
keep from transmitting all of the pressure wave.
acoustic reflex of the ossicles
muscles tighten up to reduce transmission of loud sounds by 20 dB, protecting the inner ear so all the force isn’t translated
