Origin of summating potential.

Abstract

The relationship between sound and cochlear potentials is considered in the light of von Békésy's observations of movement of the cochlear partition and Davis' variable-resistance theory of hair-cell function. An equation is derived relating hair angle to basilar-membrane movement. The equation is φ = arcot (Yα+cotφ0) where φ is the hair angle and α is proportional to basilar-membrane movement. φ0 is the resting hair angle. Y is the ratio of the distance between basilar membrane and hair cell apex to the distance between tectorial membrane and hair-cell apex. It is shown that the sigmoidal shape of this function leads to a linear dependence of microphonics on sound intensity, generation of harmonics, and production of positive and negative summating potentials by inner and outer hair cells, respectively. The behavior of the cochlear potentials, including the effect of sound pressure in reversing summating potential polarity, effect of cochlear pressure changes, and reversal of summating potential polarity with anoxia, is also accounted for. A mechanical model of the organ of Corti, used to illustrate our theory, is described, together with results obtained from the model.