[Morphological studies of the form of the cupula in the semicircular canal ampulla]

The cupula in the ampulla of the semicircular canal, like the tectorial membrane in the cochlea, forms the essential link in transferring endolymph fluid movement stimuli to the hair cells. Clear understanding of physiological cupula movement only started evolving towards the end of the 1970s. Currently, the cupula is assumed to adhere firmly to the ampulla wall, with diaphragm-like displacement in the central section and at the base.

In contrast to detailed functional descriptions, there have been very few investigations on cupula morphology. These have proved difficult due to the extremely hydrous structure, which inevitably results in shape distortion during fixation. This difficulty applies particularly to electron microscopy.

The present morphological investigations were performed in artificial endolymph on fresh preparations in the salmon (Salmo salar). After staining and isolating the cupula from the ampulla, a precise morphological investigation was performed. A relatively uniform basic structure was observed, with considerable interindividual variability in cupula shape.

Such variability suggests that impairment of cupular form can occur and could be associated with altered peripheral vestibular function.