Ear

The organ of hearing and balance. It consists of three parts: the outer ear, the middle ear, and the inner ear. The outer ear comprises the pinna and the ear canal. The outer part of the ear canal produces earwax, which traps dust and foreign bodies. The canal is closed at its inner end by the eardrum, which vibrates in response to changes in air pressure that make sound. The middle ear is a cavity that conducts sound to the inner ear by means of three tiny, linked, movable bones known as ossicles. The first bone, the malleus, is joined to the inner surface of the eardrum. The second, the incus, is linked to the malleus and to the third bone, the stapes. The base of the stapes fills the oval window leading to the inner ear. The eustachian tube links the middle ear to the back of the nose. The inner ear is an intricate series of structures deep within the skull. The front part, the cochlea, is a tube containing nerve fibres that detect different sound frequencies. The rear part of the inner ear contains three semicircular canals and is concerned with balance. The semicircular canals are connected to a cavity called the vestibule and contain hair cells bathed in fluid. Some of these cells are sensitive to gravity and acceleration; others detect direction of movement. Information from the inner ear is conducted to the brain via the