Different sound frequencies affect different areas of the basilar membrane, thus some receptors send more action potentials than others. Hair cells in the utricle and saccule respond to changes in head position with respect to gravity and movement in one direction.
Semicircular canals detect rotation of the head due to endolymph movement against the hair cells.
Hearing and Equilibrium in Other Vertebrates Fishes and aquatic amphibians have a lateral line system running along both sides of the body. Mechanoreceptors called neuromasts contain hair cell clusters whose hairs are embedded in a gelatinous cap, the cupula . Water enters the system through numerous pores on the animal's surface and flows along the tube past the neuromasts. Pressure of moving water bends the cupula causing an action potential in the hair cells. Provides information about the body's movement direction and velocity of water currents, and movements or vibrations caused by predators and prey.