The cupula is a structure in the vestibular system, sensing proprioception. The cupula is located within the ampullae of each of the three semicircular canals. As fluid rushes by the cupula, hair cells within it sense rotational acceleration, and transmit the corresponding signal to the brain through the vestibulocochlear nerve (CN VIII) In their natural orientation within the head, the cupulae are located on the medial aspect of the semicircular canals. In this orientation, the kinocilia rest on the posterior aspect of the cupula. [WP,unvetted]. [ http://en.wikipedia.org/wiki/Apex_of_cochlea ]