Anatomy of the middle ear

The tympanic membrane is approximately 1 cm in diameter; it separates the middle from the outer ear.

The ear drum is formed of three layers:

• outer epithelial layer
• middle fibrous layer
• inner mucosal layer of respiratory epithelium

The upper most part of the drum, above the lateral process of the malleus, has a relatively deficient fibrous layer and is called the pars flaccida. The rest of the drum is known as the pars tensa. The centre of the drum is called the umbro. On otoscopic examination, the lower anterior portion exhibits a light reflex.

The middle ear is an air-containing space of about 1 cubic centimetre. It contains three ear ossicles which form a chain running from the tympanic membrane to the oval window of the inner ear; the largest is the malleus which lies embedded in the tympanic membrane; the middle ossicle is the incus; the footplate of the stapes occupies the oval window.

The ossicles articulate with each other at synovial joints; the stapes with the oval window at a simple fibrous joint.

The middle ear is important because of its role in hearing and as a route for spread of infection to vital structures.