Cupulae:

gelatinous masses in the semicircular canals. The hair cells are embedded in the cupulae; distortions of the cupulae by fluid within the semicircular canals causes hair cells to be activated and to send signals about movement to the brain.

Watch this 2-Minute Neuroscience video to learn more about the vestibular system.

Read more - Know your brain: Vestibular system