STRUCTURE OF THE MACULA UTRICULI WITH SPECIAL REFERENCE TO DIRECTIONAL INTERPLAY OF SENSORY RESPONSES AS REVEALED BY MORPHOLOGICAL POLARIZATION

The anatomy of the labyrinth and the structure of the macula utriculi of the teleost fish (burbot) Lota vulgaris was studied by dissection, phase contrast, and electron microscopy. The innervating nerve fibers end at the bottom of the sensory cells where two types of nerve endings are found, granulated and non-granulated. The ultrastructure and organization of the sensory hair bundles are described, and the finding that the receptor cells are morphologically polarized by the presence of an asymmetrically located kinocilium in the sensory hair bundle is discussed in terms of directional sensitivity. The pattern of orientation of the hair cells in the macula utriculi was determined, revealing a complicated morphological polarization of the sensory epithelium. The findings suggest that the interplay of sensory responses is intimately related to the directional sensitivity of the receptor cells as revealed by their morphological polarization. The problem of efferent innervation is discussed, and it is concluded that the positional information signaled by the nerve fibers innervating the vestibular organs comprises an intricate pattern of interacting afferent and efferent impulses