Description of Some Mechanical Properties of the Organ of Corti

A short historical introduction is followed by a description of the technique for observing the organ of Corti in a lightly anesthetized guinea pig with the help of a slit lamp. The magnification was around 200 times, and stroboscopic illumination was used with a 1-kilowatt high pressure mercury-arc lamp. The relative stiffness of the Reissner's membrane, the tectorial membrane, the reticular membrane, and the Hensen cells were investigated with test needles. It was possible to demonstrate the earlier anatomical concepts of the stiffness of the reticular membrane and the pillars of Corti. In order to obtain the high sensitivity of the ear, the stiff tissues of the organ of Corti must be mechanically matched (impedance matched) to vibrating energy. of the perilymph. It was found that the organ of Corti is very well suited to work as a transformer for shearing forces. The difference between the vibration pattern of a series of resonators in the sense described by Helmholtz and the pattern of traveling waves is described. The actual observation of the membranes in the organ of Corti showed only traveling waves during stimulation with a pure tone. For every given frequency there was one point along the basilar membrane where a transition in the vibration pattern occurred, and the more radial vibrations of the organ of Corti near the stapes went over into longitudinal vibrations on the wave front facing the helicotrema. The place of transition moves with the frequency of the stimulus. Finally, the different traveling waves which may run along an elastic pad like the organ of Corti are described, and their possible roles in the cochlea are discussed. This leads to some possible explanations of why the cochlea is coiled.