The efferent system or olivocochlear function bundle - fine regulator and protector of hearing perception

Abstract

The efferent system of the ear possesses several distinct functions, in particular noise protection, mediation of selective attention and improvement of signal to noise ratio. It also supports adaptation and frequency selectivity by modification of the micromechanical properties of outer hair cells. There are many differences in anatomy and physiology between the medial and lateral olivocochlear system suggesting that they are functionally separate systems. The efferent system is affected by inner ear stressors, e.g. noise, ototoxic drugs, and might play a key role in tinnitus generation and maintenance. The anatomy, physiology and its realtionships to inner ear pathologies are discussed in this review article.

Keywords: lateral efferent system; medial efferent system; neurotransmitter; olivocochlear bundle; superior olive; tinnitus.

Figure 1

Course of the medial and lateral efferent system. A, The auditory brainstem section. Sound representations from the ear ascend to the olivary complex via the ventral afferent pathway and project back to the ear via dorsal crossed and uncrossed medial and lateral efferent fibers. B Cross-sectional view of the inner ear. The major ascending afferent pathway arises from inner hair cells. Descending olivocochlear projections terminate on inner and outer hair cells. (with permission from Liberman MC. Effects of chronic cochlear de-differentiation on auditory-nerve response. Hear Res 1990; 49: 209–224, © 1990, Elsevier; and May BJ, Budelis J, Niparko JK. Behavioral studies of the olivocohlear efferent system. Arch Otolaryngol Head Neck Surg 2004; 130: 660–664; Copyright © 2004, American Medical Association. All rights reserved).