The ossicles mechanically transform impedance to overcome fluid resistance

Evidence

In order to achieve efficient transfer of energy from the tympanic membrane to the oval window, the effective pressure acting on the oval window is arranged by mechanical means to be greater than that acting on the tympanic membrane. This is to overcome the higher resistance to movement of the cochlear fluid compared with that of air at the input to the ear. Resistance to movement can be thought of as “impedance” to movement, and the impedance of fluid to movement is high compared with that of air. The ossicles act as a mechanical “impedance converter” or “impedance transformer,” and this is achieved essentially by two means: ■ the lever effect of the malleus and incus; and ■ the area difference between the tympanic membrane and the stapes footplate. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 526

Categorization

• DEFINE: Introduces the impedance-matching concept that explains why the middle ear is built as it is.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 526
• XREF: connects to: The middle ear functions as an impedance transformer matching air to fluid; Impedance equals applied force divided by attained velocity; Tympanic membrane buckling doubles the force delivered to the malleus (+5 more)

Broader Connections

• The middle ear evolved as an impedance transformer to bridge air-water sound energy loss #corroborates (0.95) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 733
• The middle ear amplifies sound pressure through three mechanical mechanisms #expands (0.85)
• Otosclerosis stiffens ossicle movement and attenuates transmitted sound #complicates (0.75)
• Waves split into reflected and refracted parts at impedance-mismatched interfaces #exemplifies (0.70)