Malleus vibration modelled as rigid body motion.

Malleus motion is classically regarded as a rotation about a fixed axis whose location is determined by the anatomy and suspension of the middle ear ossicles. In a previous paper (1) we have shown that the mode of vibration is complex and varies with frequency. To define the malleus motion in detail, its vibration was measured interferometrically at a large number of points (about 20) on the manubrium in anesthetized cat. The viewing direction was kept fixed. A pure tone stimulus was used and the frequency was changed from 100 Hz to 25 kHz. Assuming that the malleus moves as a rigid body the observed motion can be decomposed into three components; one translational component along the direction of viewing (z axis) and two rotational components characterized by rotation vector components in the plane perpendicular to the translational component. These motion components were calculated from the experimental data. Our results show that the direction of the malleus rotation axis is changing within each cycle. Results from different animals show large interanimal variations.