Sound waves, the auditory stimulus, are directed toward the external acoustic meatus by the pinna of the outer ear and through the ear canal to the tympanic membrane (eFig. 9.79). Vibration of the tympanic membrane, induced by the incoming sound waves, is transmitted to the three ossicle bones (malleus, incus, and stapes) of the middle ear. These bones amplify sound waves so they can be converted to pressure waves at the oval window of the fluid-filled cochlea. To prevent damage from loud or high-decibel sounds, movements of the malleus and stapes are reduced by the tensor tympani and stapedius muscles.