Extremely Small Motions of the Basilar Membrane in the Inner Ear

Abstract

THERE is a great deal of speculation about the amplitudes of cochlear membrane motion calculated by various authors for the lower threshold of hearing, which indicate an order of magnitude of motion smaller than the diameter of a hydrogen atom. These deflexions are detected and converted by the hair cells into nerve impulses which are recognized by the brain. Because these motions are too small to be observed physically, the various published values are theoretical extensions of experiments performed at much higher amplitudes. For example, von Békésy^1,2 has linearly extrapolated his measurements to give 10⁻¹¹ cm r.m.s. basilar membrane motion for 1,000 Hz at the lower threshold. Because the behaviour of the auditory system is nonlinear, the calculations based on a linear model are questionable.