Transduction in semicircular ducts

The Velocity is a vector quantity; it has magnitude (speed) and direction. For the circular motion, like head rotation, even if the angular speed is kept steady, the direction in which the velocity vector is acting is constantly changing. Therefore head rotation is an angular acceleration. Both the ends of each semicircular canal insert into the utricle. In the canal is the endolymph-filled semicircular duct. At one end of each duct is the dilation, the ampulla; in which sits the ampullary crest. The Vestibular hair cells in the crest have their stereocilia embedded in a gelatinous sheet, the cupula. The Rotation of the head maximally stimulates hair cells in the canals lying in similar plane as the rotation. The Rotation of the endolymph lags behind head rotation since of its inertia, therefore the endolymph exerts a pressure distorting the cupula, and bending the stereocilia. The transduction mechanism is similar to that of hair cells in otolith organs. Since the cupula is not an ideal pressure transducer the signals transmitted by the duct afferents measure angular acceleration for slow and fast rotations, but encode the velocity for mid-range rotation speeds. The Semicircular ducts on each side lying in similar plane operate in pairs. The Head rotation which causes depolarization of hair cells in the horizontal duct of the left ear will hyperpolarize hair cells in the horizontal duct of the right ear.