Investigations on the morphology of the cupula in semicircular canal ampulla

Background and objective. The cupula in the ampulla of the semicircular can al, like the tectorial membrane in the cochlea,forms the essential link in transferring endolymph fluid movement stimuli to the hair cells. Clear unde rstanding of physiological cupula movement only started evolving towards th e end of the 1970s. Currently, the cupula is assumed to adhere firmly to th e ampulla wall, with diaphragm-like displacement in the central section and at the base. Patients/Methods. In contrast to detailed functional descriptions, there ha ve been very few investigations on cupula morphology. These have proved dif ficult due to the extremely hydrous structure, which inevitably results in shape distortion during fixation. This difficulty applies particularly to e lectron microscopy. Results. The present morphological investigations were performed in artific ial endolymph on fresh preparations in the salmon (Salmo salar). After stai ning and isolating the cupula from the ampulla,a precise morphological inve stigation was performed. A relatively uniform basic structure was observed, with considerable interindividual variability in cupula shape. Conclusions. Such variability suggests that impairment of cupular form can occur and could be associated with altered peripheral vestibular function.