Kuplakalvon

Kuplakalvon, or cupular membrane, is a gelatinous structure in the vestibular organ of the inner ear. It forms part of the crista ampullaris within each semicircular canal and extends as a dome-shaped plate into the endolymphatic space. The membrane is attached at the ampullary crest and envelops the apical surfaces of the vestibular hair cells, with their stereocilia projecting into its substance.

Structurally, kuplakalvon is a flexible extracellular matrix that lacks mineralization, unlike the otolithic membranes. It is anchored to the supporting tissue of the crista ampullaris and moves with the endolymph when the head is rotated. This movement deflects the hair bundles and transduces mechanical stimuli into neural signals.

Functionally, the cupular membrane converts angular acceleration into neural information by bending the hair cell stereocilia, thereby altering the firing rate of the vestibular nerve. Its mechanical properties determine sensitivity to head movements and contribute to the adaptation of responses during sustained rotations.

Clinical relevance is seen in disorders affecting the cupula. In cupulolithiasis, otoconia detach from the otolith organs and adhere to the cupula, causing vertigo that is provoked by specific head positions. In canalithiasis, debris free-floats within the canal, leading to transient vertigo. Diagnoses often use positional tests such as the Dix-Hallpike maneuver, and treatments may involve canalith repositioning maneuvers like the Epley procedure.

Terminology: in Swedish medical literature, kuplakalvon refers to the cupular membrane; in English texts it is commonly called the cupula or cupular membrane of the crista ampullaris.