Ear

Ear, organ of hearing and of balance. The ears convert the vibrations of air produced by sound into minute electrical impulses that can be sensed by the brain. They also contain a delicate and vital mechanism that enables the body to maintain its balance. In humans and many other higher animals, the visible part of the ear, or auricle, acts as a funnel for sound waves, directing them into the auditory canal. The auricle and the auditory canal together constitute the outer ear. The vibrations caused by sound waves first strike the eardrum, or tympanum, a membrane across the auditory canal that separates the outer ear from the middle ear. From the eardrum the vibrations are then transmitted to the 3 bones, or auditory ossicles, of the middle ear—the hammer (malleus), the anvil (incus), and the stirrup (stapes). These bones hinge on each other and act like a system of levers, transforming the relatively large but feeble vibrations of the eardrum into finer but much stronger vibrations of the same frequency. These enter the spiral-shaped cochlea of the inner ear via a small opening called the oval window. Within the fluid-filled cochlea the vibrations are converted into nerve signals and transmitted to the brain. Also within the inner ear are 3 semicircular canals and 2 saclike organs at the base where they meet. The canals are at right angles to each other. Two are vertical, one is horizontal, and they are filled with fluid. These organs send signals to the brain indicating the position and movement of the head. The signals are essential for keeping balance.