Eardrum

Template:Short description {{#invoke:other uses|otheruses}} Template:Distinguish Template:Infobox anatomy Template:Ear series In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit changes in pressure of sound from the air to the ossicles inside the middle ear, and thence to the oval window in the fluid-filled cochlea. The ear thereby converts and amplifies vibration in the air to vibration in cochlear fluid.<ref>Template:Cite journal</ref> The malleus bone bridges the gap between the eardrum and the other ossicles.<ref>Template:Cite book</ref>

Rupture or perforation of the eardrum can lead to conductive hearing loss. Collapse or retraction of the eardrum can cause conductive hearing loss or cholesteatoma.

Structure

Orientation and relations

The tympanic membrane is oriented obliquely in the anteroposterior, mediolateral, and superoinferior planes. Consequently, its superoposterior end lies lateral to its anteroinferior end.Template:Citation needed

Anatomically, it relates superiorly to the middle cranial fossa, posteriorly to the ossicles and facial nerve, inferiorly to the parotid gland, and anteriorly to the temporomandibular joint.Template:Citation needed

Regions

The eardrum is divided into two general regions: the pars flaccida and the pars tensa.<ref>Template:Cite journal</ref> The relatively fragile pars flaccida lies above the lateral process of the malleus between the Notch of Rivinus and the anterior and posterior malleal folds. Consisting of two layers and appearing slightly pinkish in hue, it is associated withTemplate:Vague Eustachian tube dysfunction and cholesteatomas.<ref>Template:Cite journal</ref>

The larger pars tensa consists of three layers: skin, fibrous tissue, and mucosa. Its thick periphery forms a fibrocartilaginous ring called the annulus tympanicus or Gerlach's ligament.<ref>Template:Cite book</ref> while the central umbo tents inward at the level of the tip of malleus. The middle fibrous layer, containing radial, circular, and parabolic fibers, encloses the handle of malleus. Though comparatively robust, the pars tensa is the region more commonly associated withTemplate:Vague perforations.<ref>Template:Cite journal</ref>

Umbo

The manubrium (Latin for "handle") of the malleus is firmly attached to the medial surface of the membrane as far as its center, drawing it toward the tympanic cavity. The lateral surface of the membrane is thus concave. The most depressed aspect of this concavity is termed the umbo (Latin for "shield boss").<ref>Gray's Anatomy (1918)</ref>

Nerve supply

Sensation of the outer surface of the tympanic membrane is supplied mainly by the auriculotemporal nerve, a branch of the mandibular nerve (cranial nerve V₃), with contributions from the auricular branch of the vagus nerve (cranial nerve X), the facial nerve (cranial nerve VII), and possibly the glossopharyngeal nerve (cranial nerve IX). The inner surface of the tympanic membrane is innervated by the glossopharyngeal nerve.<ref>Drake, Richard L., A. Wade Vogl, and Adam Mitchell. Gray's Anatomy For Students. 3rd ed. Philadelphia: Churchill Livingstone, 2015. Print. pg. 969</ref>

Clinical significance

Examination

When the eardrum is illuminated during a medical examination, a cone of light radiates from the tip of the malleus to the periphery in the anteroinferior quadrant, this is what is known clinically as 5 o'clock.Template:Citation needed

Rupture

Unintentional perforation (rupture) has been described in blast injuries<ref>Template:Cite journal</ref> and air travel, typically in patients experiencing upper respiratory congestion or general Eustachian tube dysfunction that prevents equalization of pressure in the middle ear.<ref>Template:Cite journal</ref> It is also known to occur in swimming, diving (including scuba diving),<ref>Template:Cite journal</ref> and martial arts.<ref>Template:Cite journal</ref>

Patients with tympanic membrane rupture may experience bleeding, tinnitus, hearing loss, or disequilibrium (vertigo). However, they rarely require medical intervention, as between 80 and 95 percent of ruptures recover completely within two to four weeks.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref name=Garth>Template:Cite journal</ref> The prognosis becomes more guarded as the force of injury increases.<ref name=Garth/>

Surgical puncture for treatment of middle ear infections

In some cases, the pressure of fluid in an infected middle ear is great enough to cause the eardrum to rupture naturally. Usually, this consists of a small hole (perforation), from which fluid can drain out of the middle ear. If this does not occur naturally, a myringotomy (tympanotomy, tympanostomy) can be performed. A myringotomy is a surgical procedure in which a tiny incision is created in the eardrum to relieve pressure caused by excessive buildup of fluid, or to drain pus from the middle ear. The fluid or pus comes from a middle ear infection (otitis media), which is a common problem in children. A tympanostomy tube is inserted into the eardrum to keep the middle ear aerated for a prolonged time and to prevent reaccumulation of fluid. Without the insertion of a tube, the incision usually heals spontaneously in two to three weeks. Depending on the type, the tube is either naturally extruded in 6 to 12 months or removed during a minor procedure.<ref name=Tube />

Those requiring myringotomy usually have an obstructed or dysfunctional Eustachian tube that is unable to perform drainage or ventilation in its usual fashion. Before the invention of antibiotics, myringotomy without tube placement was also used as a major treatment of severe acute otitis media.<ref name=Tube>Template:Cite journal</ref>

Society and culture

The Bajau people of the Pacific intentionally rupture their eardrums at an early age to facilitate diving and hunting at sea. Many older Bajau therefore have difficulties hearing.<ref>Template:Cite news</ref>

See also

• Middle ear
• Valsalva maneuver to equalize pressure across the eardrum

Additional images

• Anatomy of the Human Ear en.svg

  Anatomy of the human right ear.Template:Anatomy of the human ear - color legend

• Gray907.png

  External and middle ear, right side, opened from the front (coronal section)

• Gray908.png

  Horizontal section through left ear; upper half of section

• Gray912.png

  The right membrana tympani with the hammer and the chorda tympani, viewed from within, from behind, and from above

• Gray915.png

  Auditory tube, laid open by a cut in its long axis

• Gray919.png

  Chain of ossicles and their ligaments, seen from the front in a vertical, transverse section of the tympanum (tympanic cavity)

• Gray909.png

  Right eardrum as seen through a speculum

• Normal Left Tympanic Membrane.jpg

  This is a normal left eardrum.

• Tympanic membrane viewed by otoscope.png

  Tympanic membrane viewed by otoscope

• Traumatic Perforation of the Tympanic Membrane.jpg

  The oval perforation in this left tympanic membrane was the result of a slap on the ear

• Subtotal Perforation of the right tympanic membrane.tif

  A subtotal perforation of the right tympanic membrane resulting from a previous severe otitis media

• TM RIGHT NORMAL.jpg

  A normal human right tympanic membrane (eardrum)

• Frog on leaf with eardrum.jpg

  Frog on leaf showing tympanum

External links

• Diagram at Georgia State University
• drtbalu's otolaryngology online

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