ULTRASTRUCTURAL ORGANIZATION AND DEVELOPMENT OF VESTIBULAR SENSORY EPITHELIA

Abstract

Light and electron microscopy was used to study the developing and adult sensory epithelia in the vestibular labyrinth in mammals.The ultrastructure of two different types of vestibular sensory cells, type I and II was first reported by Wersall, the innervation of these cells was thoroughly described.Type I sensory cells are directly innervated by only one nerve fiber (chalice). This same chalice nerve may also innervate a neighbouring type I sensory cell. Some type II sensory cells are innervated by the chalice nerve as well as bouton shaped nerve endings. Some type II sensory cells have only bouton shaped nerve endings. Type II sensory cells have direct contact with efferent nerve endings while there is no direct contact between efferent nerve endings and type I sensory cell. Here the efferent nerve fibers form synaptic contacts with the nerve chalice or the afferent dendrite. Thus, the innervation of the vestibular sensory cells is complicate and thorough. (Fig. 2)The sensory cells can be differentiated from simple cylindrical cells when their nerve endings make synaptic contact. The afferent nerve endings in type II sensory cells first appear, then the efferent innervation in type II sensory cells and nerve chalice formation in the type I sensory cells occurrs at birth.