How do movements stimulate the hair cells in the vestibular system?

The hair cells have a special type of ion channel that is gated by mechanical deformation. Depending on which way the hair cell bends, the neuron will either become hyperpolarised or depolarised. Deformation of the hair cells is caused by two separate mechanisms depending on which part of the vestibular system is in question. For the semicircular canals (SCCs) - these are filled with a fluid, such that when the head moves, the fluid momentarily lags behind exerting pressure on a membrane called a cupula. At its base are hair cells that project up into the cupula. When the cupula is deflected, so are the hair cells. The second component is the otolithic organs. These consist of a flat, top heavy bed of tissue with hair cells at their base. When the head moves up/down or side-to-side, the tissue (otolithic membrane) momentarily lags behind and the hair cells are deformed. In both cases the transduction is mechanical -> electrical; but whereas the SCCs rely on fluid movement for the mechanical force, the otoliths don't.