The eardrum, or tympanic membrane, is a thin, cone-shaped membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear, and then to the oval window in the fluid-filled cochlea. Hence, it ultimately converts and amplifies vibration in air to vibration in fluid. The malleus bone bridges the gap between the eardrum and the other ossicles.
There are two general regions of the tympanic membrane: the pars flaccida (upper region, see picture on right) and the pars tensa. The pars flaccida consists of two layers, is relatively fragile, and is associated with eustachian tube dysfunction and cholesteatomas. The larger pars tensa region consists of three layers: skin, fibrous tissue, and mucosa. It is comparatively robust, and is the region most commonly associated with perforations.
Rupture or perforation of the eardrum can lead to conductive hearing loss. Collapse or retraction of the eardrum can also cause conductive hearing loss or even cholesteatoma.
The Bajau people of the Pacific intentionally rupture their eardrums at an early age in order to facilitate diving and hunting at sea. Many older Bajau therefore have difficulties hearing. During World War II, the German Luftwaffe was known to pierce the ear drums of fighter pilots in order to prevent air pressure issues, and even inserted grommets in the membrane to prevent the hole from healing up. Pilots involved often suffered from chronic hearing loss later in life.
Unintentional rupture of the ear drum has been described in blast injuries during conflict, but also during air travel, usually when the congestion of an upper respiratory infection has prevented equalization of pressure in the middle ear. It is also described in sport and recreation, such as swimming, diving with a poor entry into the water, scuba diving and martial arts. In the published literature, 80% to 95% have recovered completely without intervention in two to four weeks.  These injuries, even in a recreational or athletic setting, are blast injuries. Many will experience some short-lived hearing loss and ringing in the ear (tinnitus) but can be reassured that this, in all likelehood, will pass. A very few will experience temporary disequilibrium (vertigo). There may be some bleeding from the ear canal if the eardrum has been ruptured. Naturally, the foregoing reassurances become more guarded as the force of injury increases, as in military or combat situations.
External and middle ear, opened from the front. Right side.
Horizontal section through left ear; upper half of section.
The right membrana tympani with the hammer and the chorda tympani, viewed from within, from behind, and from above.
Auditory tube, laid open by a cut in its long axis.
Chain of ossicles and their ligaments, seen from the front in a vertical, transverse section of the tympanum.
Right tympanic membrane as seen through a speculum.
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