Middle Ear IV Flashcards
What is impedance determined by?
Resistance factor and reactance factor
What is resistance factor?
Loss of energy caused by friction
What is reactance factor?
Mass reactance: Objects with greater mass prefer low frequency sounds and offer greater resistance to high frequencies.
Stiffness reactance: Objects with greater stiffness are preferential/will transmit high frequency sounds and impede low frequency sounds.
Does the middle ear prefer low or high frequencies?
Prefers high frequencies, impedes low frequencies, because stiff, hard walled cavity contains a small amount of air. (less compressible)
Which has a larger effect on frequency filtering? Pinna or ear canal?
Ear canal.
What frequencies are human most sensitive to?
Most sensitive to mid-high range, then very high, then low frequency range.
The ossicular chain is dominated by ______.
Stiffness reactance.
How does the stapes react to a high intensity vs low intensity sound?
High=piston movement, low=tilting/rocking
What is the main role of the middle ear?
To function as an impedance matching device for the outer ear and the inner ear.
What three mechanisms contribute to matching impedance?
The area differential, the buckling effect, and the lever action.
What is the area differential?
Largest contributor, TM to oval window ratio. Force that is applied over tympanic membrane is directed toward a smaller structure, the stapes footplate, increasing the force per unit area.
What is the area of the TM? Of the stapes footplate? Therefore, what is the size ratio?
55mm squared/3.2mm squared= 17:1
What does the area differential translate to in terms of dB?
20-25 dB
What is the buckling effect?
Vibrations directed at the tympanic membrane cause it to buckle somewhat. This results in the malleus arm moving a shorter distance than the TM.
What gains in terms of dB are made by the buckling effect?
4-6 dB
