Organization of the sensory hairs in the gravity receptors in utricule and saccule of the squirrel monkey

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Summary

The structural organization of the sensory hairs of the gravity receptors is mainly characterized by the presence of one kinocilium and 40–110 stereocilia on each sensory cell. The spatial arrangement of the kinocilia in relation to the stereocilia presents a polarization, similar to that in the sensory epithelia of the cristae. This polarization, however, is not uniform in the maculae. The direction of polarization varies between groups of several hundred sensory cells. Within one group the sensory cells are all polarized in the same main direction and these groups are considered as functional units.

The apparent stiffness and low metabolic activity of the stereocilia suggest their mechanical transmitter function between the otolithic membrane and the sensory cells.

The presence of modified kinocilia and basal bodies in other sensory systems raises the question of their significance in sensory receptors. Their unmodified structure in the maculae, however, where the basal bodies are almost identical with centrioles, and the presence of one kinocilium with a basal body and an associated centriole in the supporting cells as well, illustrate their unspecific nature. The centrioles, which later probably become basal bodies, are in close relation to the differentiation of apical cytoplasmic structures such as the kinocilium and the cuticula. This is demonstrated by the appearance of those structures at the bottom of the sensory cell, when the centrioles are situated in this part of the cell.

This work was supported by NASA Research Grant NsC 268—62 to the Harvard University Medical School at the Dept. of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Mass, and by U.S.P.H.S. National Institute of Neurological Diseases and Blindness, Grant nos. B 3447 and B. 3779.