Editing Cochlea (section)

==Structure==
[[File:Cochlea.svg|Structural diagram of the cochlea showing how fluid pushed in at the oval window moves, deflects the cochlear partition, and bulges back out at the round window.|alt=|thumb|400x400px]]

The cochlea ({{plural form}}: cochleae) is a spiraled, hollow, conical chamber of bone, in which waves propagate from the base (near the middle ear and the [[oval window]]) to the apex (the top or center of the spiral). The spiral canal of the cochlea is a section of the bony labyrinth of the inner ear that is approximately 30&nbsp;mm long and makes 2{{frac|3|4}} turns about the modiolus. The cochlear structures include:
* Three ''scalae'' or chambers:
** the [[vestibular duct]] or ''scala vestibuli'' (containing [[perilymph]]), which lies superior to the cochlear duct and abuts the oval window
** the [[tympanic duct]] or ''scala tympani'' (containing perilymph), which lies inferior to the cochlear duct and terminates at the [[round window]]
** the [[cochlear duct]]  or ''scala media'' (containing [[endolymph]]) a region of high [[potassium]] ion concentration that the stereocilia of  the hair cells project into
* The [[helicotrema]], the location where the tympanic duct and the vestibular duct merge, at the apex of the cochlea
* [[Reissner's membrane]], which separates the vestibular duct from the cochlear duct
* The ''[[osseous spiral lamina]]'', a main structural element that separates the cochlear duct from the tympanic duct
* The [[basilar membrane]], a main structural element that separates the cochlear duct from the tympanic duct and determines the mechanical wave propagation properties of the cochlear partition
* The [[organ of Corti]], the sensory epithelium, a cellular layer on the basilar membrane, in which sensory hair cells are powered by the potential difference between the perilymph and the endolymph
* [[Hair cells (ear)|Hair cells]], sensory cells in the organ of Corti, topped with hair-like structures called [[Stereocilia (inner ear)|stereocilia]]
* The [[spiral ligament]] is a coiled thickening in the fibrous lining of the cochlear wall. It attaches the membranous cochlear duct to the bony spiral canal.

The cochlea is a portion of the inner ear that looks like a snail shell (''cochlea'' is Greek for snail).<ref>{{Cite book |title=The Kingfisher children's encyclopedia. |year=2012 |orig-year= 2011 |publisher=Kingfisher |others=Kingfisher Publications. |isbn=9780753468142 |edition=3rd ed., fully rev. and updated |location=New York |oclc=796083112}}</ref> The cochlea receives sound in the form of vibrations, which cause the stereocilia to move. The stereocilia then convert these vibrations into nerve impulses which are taken up to the brain to be interpreted. Two of the three fluid sections are canals and the third is the 'organ of Corti' which detects pressure impulses that travel along the auditory nerve to the brain. The two canals are called the vestibular canal and the tympanic canal.

=== Microanatomy ===
The walls of the hollow cochlea are made of bone, with a thin, delicate lining of [[Epithelium|epithelial tissue]]. This coiled tube is divided through most of its length by an inner membranous partition. Two fluid-filled outer spaces (ducts or ''scalae'') are formed by this dividing membrane. At the top of the snailshell-like coiling tubes, there is a reversal of the direction of the fluid, thus changing the vestibular duct to the tympanic duct. This area is called the helicotrema. This continuation at the helicotrema allows fluid being pushed into the vestibular duct by the oval window to move back out via movement in the tympanic duct and deflection of the round window; since the fluid is nearly incompressible and the bony walls are rigid, it is essential for the conserved fluid volume to exit somewhere.

The lengthwise partition that divides most of the cochlea is itself a fluid-filled tube, the third 'duct'. This central column is called the cochlear duct. Its fluid, endolymph, also contains electrolytes and proteins, but is chemically quite different from perilymph. Whereas the perilymph is rich in sodium ions, the endolymph is rich in potassium ions, which produces an [[ion]]ic, electrical potential.

The hair cells are arranged in four rows in the organ of Corti along the entire length of the cochlear coil. Three rows consist of outer hair cells (OHCs) and one row consists of inner hair cells (IHCs). The inner hair cells provide the main neural output of the cochlea. The outer hair cells, instead, mainly 'receive' neural input from the brain, which influences their [[motility]] as part of the cochlea's mechanical "pre-amplifier". The input to the OHC is from the [[olivary body]] via the medial olivocochlear bundle.

The cochlear duct is almost as complex on its own as the ear itself.  The cochlear duct is bounded on three sides by the [[basilar membrane]], the ''[[stria vascularis]]'', and Reissner's membrane.  The ''stria vascularis'' is a rich bed of capillaries and secretory cells; Reissner's membrane is a thin membrane that separates endolymph from perilymph; and the basilar membrane is a mechanically somewhat stiff membrane, supporting the receptor organ for hearing, the organ of Corti, and determines the mechanical wave propagation properties of the cochlear system.

=== Sexual dimorphism ===
Between males and females, there are differences in the shape of the human cochlea. The variation is in the twist at the end of the spiral. Because of this difference, and because the cochlea is one of the more durable bones in the skull, it is used in ascertaining the sexes of human remains found at archaeological sites.<ref>{{Cite journal |last1=Braga |first1=J. |last2=Samir |first2=C. |last3=Risser |first3=L. |last4=Dumoncel |first4=J. |last5=Descouens |first5=D. |last6=Thackeray |first6=J. F. |last7=Balaresque |first7=P. |last8=Oettlé |first8=A. |last9=Loubes |first9=J.-M. |last10=Fradi |first10=A. |date=2019-07-26 |title=Cochlear shape reveals that the human organ of hearing is sex-typed from birth |journal=Scientific Reports |language=en |volume=9 |issue=1 |page=10889 |doi=10.1038/s41598-019-47433-9 |issn=2045-2322 |pmc=6659711 |pmid=31350421|bibcode=2019NatSR...910889B }}</ref>