Tomoyuki Hoshino

Contact between the tectorial membrane and the cochlear sensory hairs in the human and the monkey

SummaryThe surface structure of the organ of Corti and the overlying tectorial membrane were studied in human and monkey cochleas under a scanning electron microscope.Imprints of small dots, indicating contact between the sensory hair tips and the tectorial membrane, were clearly seen in the outer hair cells. Imprints had a W shape composed of lines of small dots.In the human, at the base of the W, the dots were arranged in 2 or 3 lines in the lower cochlear turn and several lines in the upper turn. This pattern of dots corresponds to the structural pattern of stereocilia of the outer sensory cell; that is, the longest hairs were arranged in several lines at the base of the W and especially numerous in the upper cochlear turn. In the upper turn the lateral margin of the tectorial membrane was perforated. Imprints of the 3rd or 4th row of outer sensory cell hairs were found at the rim of these perforations.No imprints were found corresponding to the inner sensory cell hairs. Round aggregations of small granules and short strands, which were distributed along Hensens stripe in some parts of the human cochlea, suggest the presence of an indirect connection between the tectorial membrane and the inner sensory cell region.Fine grooves, clearly seen at the inner sensory cell region of the monkey cochlea, indicate a type of connection between the tectorial membrane and the sensory hair tips other than by insertion. Findings indicating contact were seen more consistently in the lower turn of the monkey.

Attachment of the Inner Sensory Cell Hairs to the Tectorial Membrane. A Scanning Electron Microscopic Study

The residue of tectorial membrane insertion of cochlear inner sensory cell hairs was studied under a scanning electron microscope. In addition to the clear imprints resulting from outer sensory cell hair insertions, an adjacent medial row of bow-shaped imprints was noted on the base of the tectorial membrane. The relative position of these imprints corresponded to the location and the size of the inner cell hairs. These imprints were thus thought to arise from the insertion of the inner sensory hair cells. Such imprints were found only in the lower turns of the cats cochlea, but not on the guinea pig tectorial membrane. Thus an actual physical contact between the tectorial membrane and the inner sensory cell hiars may exist in some species but not in others, and when there is physical contact, it is thought to be less firm than that of the outer sensory hair cells.

Scanning electron microscopic study of the cat papilla neglecta

SummaryThe papilla neglecta in the cat vestibule was studied under a scanning electron microscope. This papilla appears as a small mound of cells on the utricle near the posterior semicircular canal crista. The number of sensory hair bundles on the papilla ranged from 11–64 in 7 ears examined (average, 37). Although this crista-like endorgan was regularly found in the cat, its function may not be important in that the number of sensory hair cells is only 1/150 of those counted on guinea pig posterior semicircular canal crista.

A Scanning Electron Microscopic Study of the Crista Ampullaris in Vertebrates

The crista ampullaris from various classes of vertebrates were studied under a scanning electron microscope. These animals included the lamprey, the goldfish, the bullfrog, the tortoise, the pigeon, the guinea pig, the cat and the rhesus monkey. The lamprey has only the vertical cristae composed of a gently sloping single ridge. The oblique position of the lateral crista to the longitudinal axis of the ampulla in the goldfish is an unique finding within the vertebrates. The vertical and lateral cristae show different shapes, especially those of the bullfrog, the tortoise and the pigeon. Development of a planum semilunatum was found on both sides of the vertical crista and on the medial side of the lateral crista in these animals and the goldfish. Within the mammals, the vertical and lateral cristae have a similar shape, with a planum semilunatum on both sides of the crista.