Central Connections of the Octavolateralis System: Evolutionary Considerations

Abstract

The octavolateralis system collectively comprises four classes of sensory end organs and their neuronal connections. These end organs—the auditory and vestibular receptors of the inner ear and the electroreceptors and mechanoreceptors of the lateral line system—have as their sensory elements hair cells or cells believed to be modified hair cells. Various aspects of the octavolateralis system have been repeatedly reviewed in recent years. Information regarding receptor morphology and central anatomy and physiology can be found in this volume (Chaps. 9, 22, 23, 28 and 31–33), as well as in others (e.g., Fessard 1974; Tavolga, Popper, and Fay 1981; Northcutt and Davis 1983; Bullock and Heiligenberg 1986). In this chapter we shall consider the octavolateralis system with respect to the following question: What is the relationship between major evolutionary changes in the sensory periphery and the organization of the CNS? Comparative anatomical and physiological studies have revealed that the octavolateralis system has a complicated and apparently unusual evolutionary history including the loss, invention, and “reinvention” of various receptor classes. It is thus an ideal system to use in such an analysis.