Mechanoneural Transduction and the Primary Afferent Response

Abstract

In Chapter 2 morphological characteristics of the labyrinthine sensory epithelium and their synaptic connections with nerve endings were seen to be remarkably similar throughout the vestibular system. In both ampullary and macular structures, type I and II sensory haircells extend bundles of cilia from their apical surfaces into structural components, the cupula and the otolith membrane, which move relative to the epithelial surface in response to adequate mechanical stimulation of the end organ. This relative movement therefore causes mechanical deflection of the cilia, which in turn is associated with modulation of local electrical potential gradients apparently responsible for the control of synaptic junctions linking the sensory epithelial cells (see Chapter 2) with their primary afferent nerve terminals. In this chapter we examine first the chain of events responsible for converting mechanical deflection of the cilia into trains of action potentials in primary nerve fibers and second the informational coding of these trains expressed as a function of adequate end-organ stimulation.