Wave Motion in the Cochlea Caused by Bone Conduction

Abstract

In an effort to explain the fact that the vibration pattern of the cochlear partition is independent of the path by which the sound is transmitted to the cochlea, a mathematical analysis was performed. First, by means of the hydrodynamic principle of continuity, it was demonstrated that the vibration of the cochiear partition caused by a tone introduced into the cochlea either through the bony wall or through an artificial window can be canceled by a tone transmitted through the oval window, irrespective of the dynamic properties of the partition. Second, a general differential equation of hydrodynamic surface waves was established, which shows that transverse waves are propagated along the cochiear partition every time there is a difference in pressure between the 2 sides. According to this equation, the wavelength is independent of the place at which the sound is introduced into the cochlea. Third, it was deduced from Hamilton''s principle of stationary energy that transverse waves in the cochlea must travel from the base towards the apex, irrespective of the location of the sound source. Hence, in agreement with the expts., mathematical analysis shows that the vibration pattern of the cochiear partition does not depend upon the way in which sound is transmitted to the inner ear. Furthermore, it shows that the introduction of sound through the bones or through an artificial window does not provide any new clues for the explanation of this pattern.