Functional Significance of the Efferent Control Mechanisms

Abstract

The question of the functional significance of the efferent innervation of the vestibular system is one of the most urgent ones. Ever since the ultrastructural evidence of efferent synapses on the hair cell became available, this matter has been pondered upon by many people. A first guess would be that the efference acts as a setting mechanism of the basic hair cell activity. Results obtained with d.c. polarization which showed that it is possible to shift the working point of a hair cell up and down its S-shaped characteristic make it encouraging to think that hyperpolarization of the hair cell membrane via the efferent synapse could achieve this very effect at any rate unidirectionally by inhibition. This possibility is still to be taken seriously. Two recent findings show convincingly that the basic activity of the hair cells can be affected by efference. In one case, the activity of the hair cells in the lateral line organ of Xenopus is inhibited whenever the ventral horn cells of the spinal cord are activated for swimming movements. In the other, the same happens in a goldfish immobilized by MS 222 when the animal is subjected to an optokinetic stimulus to which paralysis prevents it from responding by an appropriate motor response.