OBSERVATION OF APICAL PART AND NERVE-TERMINALS OF HUMAN VESTIBULAR HAIR-CELLS

The human vestibular sensory epithelia of macula utriculi in 3 cases o f acoustic neurinoma were examined by conventional and intermediate vo ltage electron microscopes. The apical part and the nerve terminals of hair cells were studied by means of a computer-aided three-dimensiona l (3-D) reconstruction technique. The sensory epithelia were fairly we ll preserved. Most type I and all type II hair cells appeared as those described in the other reports. However, some type I hair cells were incompletely surrounded by nerve calyces and received direct contacts from the efferent nerve endings. These type I hair cells were also inn ervated by a few neighbouring afferent nerve calyces. The stereocilia and the cuticular plate of type I hair cells differed from those of ty pe II hair cells. The mean diameter of type I hair cell stereocilia wa s 488 +/- 59 nm and that of type II hair cells was 373 +/- 21 nm. The cuticular plate of type I hair cells resembled a cone and was about se veral times as thick as that of type II hair cells which was similar t o a flat disc.