Round window
Encyclopedia
The round window is one of the two openings into the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...

. 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
Oval window
The oval window is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.Vibrations that come into contact with the tympanic membrane travel through the three ossicles and into the inner ear...

. It allows fluid in the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

 to move, which in turn ensures that hair cells of the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...

 will be stimulated and that audition will occur.

Anatomy

The round window is situated below and a little behind the oval window
Oval window
The oval window is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.Vibrations that come into contact with the tympanic membrane travel through the three ossicles and into the inner ear...

, 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
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

 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
Saddle point
In mathematics, a saddle point is a point in the domain of a function that is a stationary point but not a local extremum. The name derives from the fact that in two dimensions the surface resembles a saddle that curves up in one direction, and curves down in a different direction...

 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
    Mucus
    In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...

    , derived from the mucous lining of the tympanic cavity
    Tympanic cavity
    The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, an expansion of the first pharyngeal pouch....

    ;
  • 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
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

, 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
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

. It would therefore not move to any useful degree leading to a hearing loss of about 60dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

. This is, unsurprisingly, the same as for conditions where the stapes itself is fixed, such as otosclerosis
Otosclerosis
Otosclerosis is an abnormal growth of bone near the middle ear. It can result in hearing loss.-Clinical description:Otosclerosis can result in conductive and/or sensorineural hearing loss...

.

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
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

 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
Cochlear implant
A cochlear implant is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing...

 surgery. It has also recently been used as a site to place middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...

 implantable hearing aid transducers. This work has been publicised by Prof. Vittorio Colletti in Verona
Verona
Verona ; German Bern, Dietrichsbern or Welschbern) is a city in the Veneto, northern Italy, with approx. 265,000 inhabitants and one of the seven chef-lieus of the region. It is the second largest city municipality in the region and the third of North-Eastern Italy. The metropolitan area of Verona...

.

External links

  • Diagram (as 'round window') at Southwest Tennessee Community College
    Southwest Tennessee Community College
    Southwest Tennessee Community College is a community college operated by the Tennessee Board of Regents in Memphis, Tennessee, USA. It is the result of a 2001 merger between two institutions started by the Regents in the 1960s, the former Shelby State Community College and the former State...

  • Overview at University of Denver
    University of Denver
    The University of Denver is currently ranked 82nd among all public and private "National Universities" by U.S. News & World Report in the 2012 rankings....

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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