Hearing and Balance Anatomy
William C. Shiel Jr. MD, FACP, FACR
The anatomy of the ear can be a little confusing, especially since the ear is responsible not only for hearing, but also for balance.
There are three components to the ear: the outer ear, the middle ear and the inner ear. All three are involved in hearing but only the inner ear is responsible for balance.
The outer ear is composed of the pinna, or ear lobe, and the external auditory canal. Both structures funnel sound waves towards the ear drum or tympanic membrane allowing it to vibrate. The pinna is also responsible for protecting the ear drum from damage. Modified sweat glands in the ear canal form ear wax .
The middle ear is an air filled space located in the temporal bone of the skull. Air pressure is equalized in this space via the Eustachian
tube which drains into the nasopharynx or the back of the throat and nose. There are three small bones, or ossicles, that are located adjacent to the tympanic membrane. The malleus, incus, and stapes are attached like a chain to the tympanic membrane and convert sound waves that vibrate the membrane into mechanical vibrations of the three bones. The stapes fills the oval window which is the connection to the inner ear.
The inner has two functions; the first is hearing and the second is balance. It is a warren of tubes filled with fluid encased within the temporal bone of the skull. The bony tubes also contain a set of cell membrane lined tubes. The bony tubes are called the bony labyrinth filled with perilymph fluid, which the membranous labyrinth tubes are filed with endolymph. This is where the cells responsible for hearing are located (the hairy cells of Corti).