Sound waves from the external environment are received by the pinna. The received sound waves pass through the auditory meatus and strike the tympanic membrane. It vibrates the tympanic membrane. These vibrations reach the fenestra ovalis through the malleus, incus and stapes. From the fenestra ovalis passes into the perilymph. In the perilymph, the power of sound waves is increased about 20 times. It stimulates the sensory fibers of the organ of corti and generates nerve impulses. These nerve impulses reach the hearing center of the brain through the auditory nerve and the person hears sound.
At the root of the semicircular duct of the inner ear is the ampulla. Inside the ampulla are endolymph and sensory hair cells. A jelly-like cupula is attached to the follicles. The endolymph and cupula are positioned in the direction in which the human head turns or bends. Sensory cells send this message to the brain. Again, utriculus and saccule have organ called saculae. The saccule carries sensory rhombic cells. When the head tilts to one side, the otolith grains exert pressure on the hair follicles. The hair cells are stimulated and the sensation reaches the brain through the nerves. Then man can understand his relative position. Muscle contraction returns the head to its normal position. Immediately the balance of the body is maintained.