Observations of the organ of Corti under in vivo-like conditions.

The organ of Corti of the rat has been investigated within minutes after death in different fluids bathing the organ of Corti. Static compliance of the tectorial membrane across the membrane was measured by microsprings, and the response of the membrane to a vibrating micro-electrode was studied. In addition, fluid motion about the organ caused by the placement of a vibrating micro-electrode on the tectorial membrane was observed. The static compliance of the tectorial membrane was unaffected by the bathing solutions. Dynamic characteristics of the membrane could be completed altered by the addition of aldehyde solutions. As the cochleas used by von Békésy (1960) were preserved in formaldehyde solutions, it is concluded that his observations regarding the dynamic characteristics of the tectorial membrane were in part artifact. It is suggested that a proper description of the mechanisms of the organ of Corti must include a tectorial membrane whose limbal attachment allows for both rotation and displacement. Such a description is presented. A streaming of fluid was observed directed from Hensen's cells toward the cochlea wall. Possible mechanisms for the generation of this streaming are discussed.

Fluid motion in the mammalian organ of Corti. A possible source of the second filter.

A mechanical analysis of the functioning of the mammalian organ of Corti as deduced from experimental observations and electronmicroscopic studies of the organ has been conducted. It was found that the arch of Corti is responsible for initiating a fluid motion in the spiral sulcus and reticular lamina which could stimulate the inner hair cells. A three-dimensional linear mathematical model with no arbitrary parameters is proposed to describe the force acting on the inner hair cell cilia as a function of arch displacement. Analysis of the model results show that the model (a) correctly predicts the form of the neural response for a low frequency square wave of arch motion, (b) demonstrates a physiologically reasonable time constant of 245 musec, (c) shows a sharpening of neural stimulation of physiological importance, (d) can explain the qualitative difference of neural responses to arch motions of opposite polarity, (e) demonstrates a phase difference between outer and inner hair cell stimulation, and (f) appears to be chemically and metabolically vulnerable.