In Depth: Ear
The ears are organs that provide two main functions — hearing and balance — that depend on specialized receptors called hair cells.
- Hearing: The eardrum vibrates when sound waves enter the ear canal. Ossicles, three tiny bones (including the stapes, the smallest bone in the body), pass vibrations to the oval window, which is a membrane at the entrance to the inner ear.
- Balance: Balance is achieved through a combination of the sensory organ in the inner ear, visual input, and information received from receptors in the body, especially around joints. The information processed in the cerebellum and cerebral cortex of the brain allows the body to cope with changes in speed and the direction of the head.
The ear is divided into three parts:
- Outer ear: The outer ear includes an ear canal that is is lined with hairs and glands that secrete wax. This part of the ear provides protection and channels sound. The auricle or pinna is the most visible part of the outer ear and what most people are referring to when they use the word “ear.”
- Middle ear: Three tiny bones — the malleus, incus, and stapes — within the middle ear transfer sound vibrations from the eardrum to the inner ear. The middle ear is important because it is filled with numerous air spaces, which provide routes for infections to travel. It is also the location of the Eustachian tube, which equalizes the air pressure between the inner and outer surfaces of the tympanic membrane (eardrum).
- Inner ear: The inner ear, also called the labyrinth, operates the body’s sense of balance and contains the hearing organ. A bony casing houses a complex system of membranous cells. The inner ear is called the labyrinth because of its complex shape. There are two main sections within the inner ear: the bony labyrinth and the membranous labyrinth. The cochlea, the hearing organ, is located inside the inner ear. The snail-like cochlea is made up of three fluid-filled chambers that spiral around a bony core, which contains a central channel called the cochlear duct. Inside the cochlear duct is the main hearing organ, the spiral shaped organ of Corti. Hair cells inside the organ of Corti detect sound and send the information through the cochlear nerve.
Sound waves enter through the outer ear, move into the middle ear, and finally reach the inner ear and its intricate network of nerves, bones, canals, and cells.