fenestra rotunda

Round window
	View of the inner wall of the tympanum. (label is 'fen. rotund.' - lower of two black circles.)
	Interior of right osseous labyrinth. (label is 'cochlear fenestra', at bottom center.)
Latin	fenestra cochleae, fenestra rotunda
Gray's	subject #232 1051
MeSH	Round+Window

WordNet

fenestra leading into the cochlea (同)fenestra_cochleae, round_window, fenestra of the cochlea
a building having a circular plan and a dome
a large circular room
spherical in shape
a small opening covered with membrane (especially one in the bone between the middle and inner ear)

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丸屋根のある円形建築;丸天井の円形大広間
《時におどけて》丸々と太った / (声が)朗々とした

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/12/20 08:44:19」(JST)

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The round window is one of the two openings into the inner ear. It is closed off from the middle ear by the round window membrane, which vibrates with opposite phase to vibrations entering the inner ear through the oval window. It allows fluid in the cochlea to move, which in turn ensures that hair cells of the basilar membrane will be stimulated and that audition will occur.

Anatomy

The round window is situated below and a little behind the oval window, from which it is separated by a rounded elevation, the promontory.

It is placed at the bottom of a funnel-shaped depression (the round window niche) and, in the macerated bone, opens into the cochlea of the internal ear; in the fresh state it is closed by a membrane, the secondary tympanic membrane or round window membrane, which is a complex saddle point shape. The visible central portion is concave toward the tympanic cavity and convex toward the cochlea but towards the edges, where it is hidden in the round window niche, it curves the other way.

This membrane consists of three layers:

an external, or mucous, derived from the mucous lining of the tympanic cavity;
an internal, from the lining membrane of the cochlea;
and an intermediate, or fibrous layer.

Both the oval and round windows are about the same size, approximately 2.5 mm². The entrance to the round window niche is often much smaller than this.

Function

The stapes bone transmits movement to the oval window. As the stapes footplate moves into the oval window, the round window membrane moves out, and this allows movement of the fluid within the cochlea, leading to movement of the cochlear inner hair cells and thus hearing. If the round window were to be absent or rigidly fixed (as can happen in some congenital abnormalities), the stapes footplate would be pushing incompressible fluid against the unyielding walls of the cochlea. It would therefore not move to any useful degree leading to a hearing loss of about 60dB. This is, unsurprisingly, the same as for conditions where the stapes itself is fixed, such as otosclerosis.

Medical implications

The round window sometimes fails to develop correctly and causes the hearing loss mentioned above. Unfortunately round window malformations are often associated with other ear malformations and the hearing loss can be much more severe. Some types of ear surgery (now generally abandoned) used to leave the round window open to the outside world and covered over the oval window. Sound pressure therefore hit the round window but was shielded from the oval window. It therefore travelled "backwards" around the cochlea but still gave useful hearing as the hair cells were still deflected in the same way. The round window is often used as an approach for cochlear implant surgery. It has also recently been used as a site to place middle ear implantable hearing aid transducers. This work has been publicised by Prof. Vittorio Colletti in Verona.^[1]

Additional images

Cochlea

Notes

^ Colletti V, Soli SD, Carner M, Colletti L (2006). "Treatment of mixed hearing losses via implantation of a vibratory transducer on the round window". International journal of audiology 45 (10): 600–8. doi:10.1080/14992020600840903. PMID 17062502.

External links

Diagram (as 'round window') at Southwest Tennessee Community College
Overview at University of Denver

This article incorporates text from a public domain edition of Gray's Anatomy.

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… Fenestra rotunda, 3. … Fenestra ovalis und 4. … Beim Zustandekommen irgend welcher Störungen der Vorhofsfunktionen bei oder nach der Läsion der Cochlea, Fenestra rotunda et ovalis werden im Spatium endolymphaticum vestibuli durch die betreffende Verletzung pathologische Veränderungen hervorgerufen. …
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