Hearing

Hearing, one of the five senses, the physiological process of perceiving sound. Mammalian ears may be subdivided into three parts: outer, middle, and inner.

The outer ear is the visible, external part of the ear. It collects sound waves and channels them into the external auditory canal, towards the tympanic membrane (eardrum), which separates the outer ear from the middle ear. The tympanic membrane vibrates as the sound waves hit it. These vibrations are amplified and transmitted across the air-filled middle ear by the movement of a chain of three tiny bones, the auditory ossicles, and pass into the inner ear via a second membrane, the oval window.

The inner ear is a complex system of fluid-filled cavities and ducts.The essential organ of hearing, the Organ of Corti, lies within the coiled duct called the cochlea. Movement of the oval window disturbs the fluid of the cochlea which in turn distorts the Organ of Corti causing hair cells on this membrane to fire off impulses to the brain via the auditory nerve. The louder the sound, the more frequently the nerve impulse is repeated. The location of the hair cells sending the impulse informs the brain of the sound's pitch.