Human Biology
... (b) After sound waves cause the vibration of the tympanic membrane and pass through the ossicles, the movement reaches the middle ear. The oval window is pushed in and out, which causes waves of movement in the perilymph of the scala vestibuli. Movements of the perilymph distort the membranes and bring about movements in the endolymph inside the cochlear duct. Hair cells of the organ of Corti are stimulated and nerve impulses are transmitted to the brain. At the same time stimulation of the sensory cells is occurring, movement in the perilymph in the scala tympani reaches the round window, the round window moves in and out in the opposite direction to the oval window. (c) Utricle & Saccule The utricle and saccule provide information about the position of the head when it is stationary. Inside the utricle and saccule are sensory hair cells. The hair cells are embedded in a jelly-like layer containing small particles of calcium carbonate called otoliths. These increase the weight of the jelly so that it presses on the hairs, causing the sensory cells to send nerve impulses via the auditory nerve to the brain. When the head is tilted the otoliths pulled by gravity, slide downwards moving the whole layer of jelly, which moves the sensory hairs. A different pattern of nerve impulses is sent from the sensory hair cells to the brain, providing information of the new position of the head. Semicircular Canals Located in a part of the bony labyrinth the Semicircular Canals consist of 3 bony tubes arranged in 3 planes at right angles to each other. The Semicircular Canals can detect movement of the head in any direction. When the head moves, the semicircular canals move, but the fluid inside each canal tends to lag behind. This causes movement of the jelly covering the sensory hairs in the ampulla, the hairs are then bent and the nerve impulses initiated are sent through the auditory nerve then to the brain. The signals reaching the brain from the semicircular canals are coordinated...