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Eardrum
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The tympanic membrane, colloquially known as the eardrum, is a thin membrane that separates the external ear from the middle ear. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles.
Rupture or perforation of the eardrum can lead to conductive hearing loss.
Contents
- 1 Development
- 2 Clinical Aspects
- 3 Additional images
- 4 External links
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Development
The tympanic membrane forms from the joining of the expanding first
pharyngeal pouch and
groove. Around day 30 of
gestation, the
endoderm-lined first pharyngeal pouch expands to form the
tympanic cavity, which subsequently envelops the inner ear
ossicles. Simultaneously, the first pharyngeal groove, which is lined with ectoderm, expands to form the developing
external auditory meatus. Separated by a thin layer of
splanchnic mesoderm, the tympanic cavity and external auditory meatus join to form the tympanic membrane. As a result, the tympanic membrane is one of very few adult structures that is derived from all three
germ layers. The skin that covers the outer surface of the tympanic membrane is derived from
ectoderm, the fibrous tissue that forms the actual membrane is derived from
mesoderm, and the mucus membrane that lines the inner surface of the membrane is derived from
endoderm.
Clinical Aspects
When examining the tympanic membrane with an otoscope, a bright cone of light is seen in the anterior-inferior part of the membrane. This light is known as the "cone of light." The tympanic membrane is separated into four quadrants, with the center of the four quadrants being the umbo. Nerves, specifically the chorda tympani nerve, and arteries pass through the layers of the superior portion of the membrane. Thus, when the tympanic membrane needs to be incised for medical procedures, ENT surgeons will always cut through the inferior and posterior part of the membrane to avoid the vasculature, nerves, and bones associated with the membrane.
Additional images
External and middle ear, opened from the front. Right side.
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Horizontal section through left ear; upper half of section.
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The right membrana tympani with the hammer and the chorda tympani, viewed from within, from behind, and from above.
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Auditory tube, laid open by a cut in its long axis.
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Chain of ossicles and their ligaments, seen from the front in a vertical, transverse section of the tympanum.
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