Auditory structure and function in the mouse middle ear: An evaluation by SEM and capacitive probe

Summary

• 1. The anatomic structures of the mouse middle ear were identified and examined with scanning electron microscopy and the area and lever ratios were measured in a number of ears.

• 2. The displacement and velocity response at 100 dB for test frequencies between 1.5 and 35.0 kHz were measured with a capacitive probe at three locations: The tip of the long process of the malleus, the transverse portion of the malleus, and the head of the incus.

• 3. The velocity vs frequency response curve at the tip of the malleus resembled a high-pass filter with a resonant frequency around 12.0 kHz, and a high and low frequency roll-off of about 1.4 dB and 6.7 dB/octave respectively.

• 4. The displacement response at the tip of the malleus was linear for stimulus intensities between 100 and 130 dB.

• 5. A comparison of the velocity frequency response curves measured at the tip of the malleus, at the transverse portion of the malleus, and at the head of the incus, provided some indication of the complexity of ossicular motion in the middle ear.

• 6. The shape of the inverse velocity curve at the transverse portion of the malleus was nearly identical to the threshold sensitivity curve of the mouse above 4.0 kHz.