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The round window is one of the two openings from the
middle ear The middle ear is the portion of the ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is t ...

middle ear
into the
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear T ...

inner ear
. It is sealed by the secondary tympanic membrane (round window membrane), which vibrates with opposite phase to vibrations entering the inner ear through the
oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, ...
. It allows fluid in the
cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opene ...

cochlea
to move, which in turn ensures that hair cells of the
basilar membrane The basilar membrane is a stiff structural element within the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (c ...
will be stimulated and that audition will occur.


Structure

The round window is situated below (inferior to) and a little behind (posterior to) the oval window, from which it is separated by a rounded elevation, the
promontory A promontory is a raised mass of land Land is the solid surface of Earth that is not permanently submerged in water. Most but not all land is situated at elevations above sea level (variable over geologic time frames) and consists mainly of ...
. It is located at the bottom of a funnel-shaped depression (the round window niche) and, in the
macerated In food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life ...
bone, opens into the
cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opene ...

cochlea
of the
internal ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear T ...
; in the fresh state it is closed by a membrane, the secondary tympanic membrane (Latin: ''membrana tympani secundaria'', or ''membrana fenestrae cochleae'') or round window membrane, which is a complex
saddle point In mathematics, a saddle point or minimax point is a Point (geometry), point on the surface (mathematics), surface of the graph of a function where the slopes (derivatives) in orthogonal directions are all zero (a Critical point (mathematics), ...

saddle point
shape. The visible central portion is concave (curved inwards) toward the tympanic cavity and convex (curved outwards) 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 ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body and covers the surface of internal organs. It consists ...
, derived from the mucous lining of the
tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear The middle ear is the portion of the ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three ...
; * an internal, from the lining membrane of the cochlea; * and an intermediate, or
fibrous Fiber or fibre (from la, fibra, links=no) is a #Natural fibers, natural or #Man-made fibers, man-made substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest enginee ...
layer. The membrane vibrates with opposite phase to vibrations entering the cochlea through the
oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, ...
as the fluid in the cochlea is displaced when pressed by the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its Annular ligament of stapes, annular ligam ...
at the oval window. This ensures that hair cells of the
basilar membrane The basilar membrane is a stiff structural element within the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (c ...
will be stimulated and that audition will occur. Both the oval and round windows are about the same size, approximately . The entrance to the round window niche is often much smaller than this.


Function

The
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its Annular ligament of stapes, annular ligam ...
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 Hair cells are the sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal that coordinates its Be ...
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 60
dB
dB
. This is, unsurprisingly, the same as for conditions where the stapes itself is fixed, such as
otosclerosis Otosclerosis is a condition of the middle ear The middle ear is the portion of the ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear T ...
.


Imaging

The round window is located within the mesotympanum, at the posterior extremity of the basal turn of the
cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opene ...

cochlea
. The
oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, ...
s is also located within the mesotympanum, opening at the inferior and lateral part of the
vestibule Vestibule or Vestibulum can have the following meanings, each primarily based upon a common origin, from early 17th century French, derived from Latin ''vestibulum, -i n.'' "entrance court". Anatomy In general, vestibule is a small space or cavity ...
. Both can be seen readily on CT.


Clinical significance

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 A cochlear implant (CI) is a surgically implanted neuroprosthesis that provides a person who has bilateral moderate-to-profound sensorineural hearing loss Sensorineural hearing loss (SNHL) is a type of hearing loss Hearing loss is a partial ...

cochlear implant
surgery. It has also recently been used as a site to place
middle ear The middle ear is the portion of the ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is t ...

middle ear
implantable hearing aid transducers. This work has been publicised by Prof. Vittorio Colletti in
Verona Verona ( , ; vec, Verona or ''Veròna'') is a city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia' ...

Verona
.


Additional images

File:Cochlea.svg, Cochlea


See also

*
Oval window The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, ...


References


External links


Diagram (as 'round window')
at
Southwest Tennessee Community College Southwest Tennessee Community College is a public community college A community college is a type of educational institution An educational institution is a place where people of different ages gain an education, including preschools, childc ...

Southwest Tennessee Community College

Overview
at
University of Denver The University of Denver (DU) is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, after an absence of ...

University of Denver
{{Authority control Auditory system Ear