View source for Cochlea

{{Short description|Snail-shaped part of inner ear involved in hearing}}
{{Infobox anatomy
| Name        = Cochlea
| Latin       = cochlea
| Greek     = κοχλίας
| Image       = Cochlea-crosssection.svg
| Caption     = Cross section of the cochlea
| Image2      = {{Inner ear map|Cochlea|Inline=1}}
| Caption2    = Parts of the inner ear, showing the cochlea
| Precursor   =
| System      = [[Auditory system]]
| part_of = [[Inner ear]]
| Artery      =
| Vein        =
| Nerve       =
| Lymph       =
| pronunciation = {{IPAc-en|ˈ|k|ɒ|k|l|i|ə|,_|ˈ|k|oʊ|k|l|i|ə}}<ref>{{cite Dictionary.com|cochlea}}</ref>
}}
{{ear series|expanded=Inner}}
[[File:3DPX-002432 Cochlea and semicircular canals Nevit Dilmen.stl|thumb|3D model of cochlea and semicircular canals]]
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 (cochlea)|modiolus]].<ref>
{{cite book| title     = Atlas of anatomy|author1=Anne M. Gilroy |author2=Brian R. MacPherson |author3=Lawrence M. Ross | publisher = Thieme| year      = 2008| isbn      = 978-1-60406-151-2| page      = 536| url       = https://books.google.com/books?id=wFkxkpPcBoUC&pg=PA536 }}</ref><ref>{{cite book |last1=Moore |last2=Dalley |name-list-style=amp |title=Clinically Oriented Anatomy |edition=4th |year=1999 |page=974 |publisher=Lippincott Williams & Wilkins |isbn=0-683-06141-0 }}</ref> A core component of the cochlea is the [[organ of Corti]], the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.

==Etymology==
The name 'cochlea' is derived from the Latin word for ''snail shell'', which in turn is from the [[Greek language|Ancient Greek]] κοχλίας ''kokhlias'' ("snail, screw"), and from κόχλος ''kokhlos'' ("spiral shell")<ref>[http://www.etymonline.com/index.php?search=cochlea&searchmode=none etymology of "cochleㄷa"],</ref> in reference to its coiled shape; the cochlea is coiled in mammals with the exception of [[monotreme]]s.

==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>

==Function==
[[File:Journey of Sound to the Brain.ogg|thumb|How sounds make their way from the source to the brain|400x400px]]
The cochlea is filled with a watery liquid, the [[endolymph]], which moves in response to the vibrations coming from the middle ear via the oval window. As the fluid moves, the cochlear partition (basilar membrane and organ of Corti) moves; thousands of [[hair cell]]s sense the motion via their [[stereocilia (inner ear)|stereocilia]], and convert that motion to electrical signals that are communicated via neurotransmitters to many thousands of nerve cells. These primary auditory neurons transform the signals into electrochemical impulses known as [[action potential]]s, which travel along the auditory nerve to structures in the brainstem for further processing.

===Hearing===
{{Main|Hearing}}

The ''[[stapes]]'' (stirrup) ossicle bone of the middle ear transmits vibrations to the ''[[fenestra ovalis]]'' (oval window) on the outside of the cochlea, which vibrates the perilymph in the ''vestibular duct'' (upper chamber of the cochlea). The ossicles are essential for efficient coupling of sound waves into the cochlea, since the cochlea environment is a fluid–membrane system, and it takes more pressure to move sound through fluid–membrane waves than it does through air. A pressure increase is achieved by reducing the area ratio from the tympanic membrane (drum) to the oval window (''stapes'' bone) by 20. As pressure = force/area, results in a pressure gain of about 20 times from the original sound wave pressure in air. This gain is a form of [[impedance matching]] – to match the soundwave travelling through air to that travelling in the fluid–membrane system.

At the base of the cochlea, each 'duct' ends in a membranous portal that faces the middle ear cavity: The [[vestibular duct]] ends at the [[oval window]], where the footplate of the ''stapes'' sits. The footplate vibrates when the pressure is transmitted via the ossicular chain. The wave in the perilymph moves away from the footplate and towards the [[helicotrema]]. Since those fluid waves move the cochlear partition that separates the ducts up and down, the waves have a corresponding symmetric part in perilymph of the tympanic duct, which ends at the round window, bulging out when the oval window bulges in.

The perilymph in the vestibular duct and the [[endolymph]] in the cochlear duct act mechanically as a single duct, being kept apart only by the very thin [[Reissner's membrane]].
The vibrations of the endolymph in the cochlear duct displace the basilar membrane in a pattern that peaks a distance from the oval window depending upon the soundwave frequency. The [[organ of Corti]] vibrates due to [[outer hair cell]]s further amplifying these vibrations. [[Inner hair cell]]s are then displaced by the vibrations in the fluid, and depolarise by an influx of K+ via their [[tip-link]]-connected channels, and send their signals via neurotransmitter to the primary auditory neurons of the [[spiral ganglion]].<ref>{{cite journal |last1=Nin |first1=Fumiaki |last2=Hibino |first2=Hiroshi |last3=Doi |first3=Katsumi |last4=Suzuki |first4=Toshihiro |last5=Hisa |first5=Yasuo |last6=Kurachi |first6=Yoshihisa |title=The endocochlear potential depends on two K + diffusion potentials and an electrical barrier in the stria vascularis of the inner ear |journal=Proceedings of the National Academy of Sciences |date=5 February 2008 |volume=105 |issue=5 |pages=1751–1756 |doi=10.1073/pnas.0711463105|doi-access=free |pmid=18218777 |pmc=2234216 }}</ref>

The hair cells in the organ of Corti are tuned to certain sound frequencies by way of their location in the cochlea, due to the degree of stiffness in the basilar membrane.<ref>{{cite journal |author = Guenter Ehret |date = Dec 1978 |title = Stiffness gradient along the basilar membrane as a way for spatial frequency analysis within the cochlea |url = http://vts.uni-ulm.de/docs/2009/6797/vts_6797_9398.pdf |journal = J Acoust Soc Am | volume = 64 |issue = 6|pages = 1723–6 |pmid = 739099 | doi=10.1121/1.382153}}</ref> This stiffness is due to, among other things, the thickness and width of the basilar membrane,<ref>{{Cite book |last=Camhi |first=Jeffrey M. |url=https://archive.org/details/neuroethologyner0000camh |title=Neuroethology : nerve cells and the natural behavior of animals |date=1984 |publisher=Sunderland, Mass. : Sinauer Associates |isbn=978-0-87893-075-3}}</ref> which along the length of the cochlea is stiffest nearest its beginning at the oval window, where the stapes introduces the vibrations coming from the eardrum. Since its stiffness is high there, it allows only high-frequency vibrations to move the basilar membrane, and thus the hair cells.  The farther a wave travels towards the cochlea's apex (the ''helicotrema''), the less stiff the basilar membrane is; thus lower frequencies travel down the tube, and the less-stiff membrane is moved most easily by them where the reduced stiffness allows: that is, as the basilar membrane gets less and less stiff, waves slow down and it responds better to lower frequencies. In addition, in mammals, the cochlea is coiled, which has been shown to enhance low-frequency vibrations as they travel through the fluid-filled coil.<ref>{{cite journal |vauthors=Manoussaki D, Chadwick RS, Ketten DR, Arruda J, Dimitriadis EK, O'Malley JT |year = 2008 | title = The influence of cochlear shape on low-frequency hearing |journal = Proc Natl Acad Sci U S A |volume = 105 |issue = 16| pages = 6162–6166 |doi = 10.1073/pnas.0710037105 |pmid=18413615 |pmc=2299218 |bibcode = 2008PNAS..105.6162M |doi-access = free }}</ref>  This spatial arrangement of sound reception is referred to as [[tonotopy]].

For very low frequencies (below 20&nbsp;Hz), the waves propagate along the complete route of the cochlea – differentially up vestibular duct and tympanic duct all the way to the ''helicotrema''. Frequencies this low still activate the organ of Corti to some extent but are too low to elicit the perception of a [[pitch (psychophysics)|pitch]].  Higher frequencies do not propagate to the ''helicotrema'', due to the stiffness-mediated tonotopy.

A very strong movement of the basilar membrane due to very loud noise may cause hair cells to die. This is a common cause of partial hearing loss and is the reason why users of firearms or heavy machinery often wear [[earmuff]]s or [[earplug]]s.

=== Pathway to the brain ===
To transmit the sensation of sound to the brain, where it can be processed into the perception of ''hearing'', hair cells of the cochlea must convert their mechanical stimulation into the electrical signaling patterns of the nervous system. Hair cells are modified [[neuron]]s, able to generate action potentials which can be transmitted to other nerve cells. These action potential signals travel through the [[vestibulocochlear nerve]] to eventually reach the anterior [[Medulla oblongata|medulla]], where they [[synapse]] and are initially processed in the [[Cochlear nucleus|cochlear nuclei]].<ref name=":0">{{Cite book |last=Martin |first=John Harry |title=Neuroanatomy: Text and Atlas |publisher=McGraw Hill |year=2021 |isbn=978-1-259-64248-7 |edition=5th |location=New York |language=English |chapter=Chapter 8: The Auditory System}}</ref>

Some processing occurs in the cochlear nuclei themselves, but the signals must also travel to the [[superior olivary complex]] of the [[pons]] as well as the [[Inferior colliculus|inferior colliculi]] for further processing.<ref name=":0" />

===Hair cell amplification===
Not only does the cochlea receive sound, a healthy cochlea generates and amplifies sound when necessary. Where the organism needs a mechanism to hear very faint sounds, the cochlea amplifies by the reverse [[Transduction (physiology)|transduction]] of the OHCs, converting electrical signals back to mechanical in a positive-feedback configuration. The OHCs have a protein motor called [[prestin]] on their outer membranes; it generates additional movement that couples back to the fluid–membrane wave. This "active amplifier" is essential in the ear's ability to amplify weak sounds.<ref>{{Cite journal|last=Ashmore|first=Jonathan Felix|author-link=Jonathan Ashmore|year=1987|title=A fast motile response in guinea-pig outer hair cells: the cellular basis of the cochlear amplifier|journal=[[The Journal of Physiology]]|language=en|volume=388|issue=1|pages=323–347|doi=10.1113/jphysiol.1987.sp016617|issn=1469-7793|pmid=3656195 |pmc=1192551}} {{open access}}</ref><ref>{{Cite journal|last=Ashmore|first=Jonathan|s2cid=17722638|author-link=Jonathan Ashmore|date=2008|title=Cochlear Outer Hair Cell Motility|journal=[[Physiological Reviews]]|language=en|volume=88|issue=1|pages=173–210|doi=10.1152/physrev.00044.2006|issn=0031-9333|pmid= 18195086}} {{open access}}</ref>

The active amplifier also leads to the phenomenon of soundwave vibrations being emitted from the cochlea back into the ear canal through the middle ear (otoacoustic emissions).

===Otoacoustic emissions===

[[Otoacoustic emission]]s are due to a wave exiting the cochlea via the oval window, and propagating back through the middle ear to the eardrum, and out the ear canal, where it can be picked up by a microphone.  Otoacoustic emissions are important in some types of tests for [[hearing impairment]], since they are present when the cochlea is working well, and less so when it is suffering from loss of OHC activity. Otoacoustic emissions also exhibit sex dimorphisms, since females tend to display higher magnitudes of otoacoustic emissions. Males tend to experience a reduction in otoacoustic emission magnitudes as they age. Women, on the other hand, do not experience a change in otoacoustic emission magnitudes with age.<ref>Mishra, Srikanta K.1,2; Zambrano, Samantha2,3; Rodrigo, Hansapani4. Sexual Dimorphism in the Functional Development of the Cochlear Amplifier in Humans. Ear and Hearing 42(4):p 860-869, July/August 2021. | DOI: 10.1097/AUD.0000000000000976</ref>

===Role of gap junctions===
Gap-junction proteins, called [[connexin]]s, expressed in the cochlea play an important role in auditory functioning.<ref>{{Cite journal | last1 = Zhao | first1 = H. -B. | last2 = Kikuchi | first2 = T. | last3 = Ngezahayo | first3 = A. | last4 = White | first4 = T. W. | title = Gap Junctions and Cochlear Homeostasis | doi = 10.1007/s00232-005-0832-x | journal = Journal of Membrane Biology | volume = 209 | issue = 2–3 | pages = 177–186 | year = 2006 | pmid = 16773501 | pmc =1609193 }}</ref> Mutations in gap-junction genes have been found to cause syndromic and nonsyndromic deafness.<ref>{{Cite journal | last1 = Erbe | first1 = C. B. | last2 = Harris | first2 = K. C. | last3 = Runge-Samuelson | first3 = C. L. | last4 = Flanary | first4 = V. A. | last5 = Wackym | first5 = P. A. | title = Connexin 26 and Connexin 30 Mutations in Children with Nonsyndromic Hearing Loss | doi = 10.1097/00005537-200404000-00003 | journal = The Laryngoscope | volume = 114 | issue = 4 | pages = 607–611 | year = 2004 | pmid = 15064611 | s2cid = 25847431 }}</ref>  Certain connexins, including [[GJB6|connexin 30]] and [[GJB2|connexin 26]], are prevalent in the two distinct gap-junction systems found in the cochlea.  The epithelial-cell gap-junction network couples non-sensory epithelial cells, while the connective-tissue gap-junction network couples connective-tissue cells.<ref>{{cite journal |last1=Wang |first1=Bo |last2=Hu |first2=Bohua |last3=Yang |first3=Shiming |title=Cell junction proteins within the cochlea: A review of recent research |journal=Journal of Otology |date=December 2015 |volume=10 |issue=4 |pages=131–135 |doi=10.1016/j.joto.2016.01.003|pmid=29937796 |pmc=6002592 }}</ref>  Gap-junction channels recycle potassium ions back to the endolymph after [[mechanotransduction]] in [[hair cells]].<ref>{{Cite journal | doi = 10.1016/S0165-0173(99)00076-4 | last1 = Kikuchi | first1 = T. | last2 = Kimura | first2 = R. S. | last3 = Paul | first3 = D. L. | last4 = Takasaka | first4 = T. | last5 = Adams | first5 = J. C. | title = Gap junction systems in the mammalian cochlea | journal = Brain Research. Brain Research Reviews | volume = 32 | issue = 1 | pages = 163–166 | year = 2000 | pmid = 10751665| s2cid = 11292387 }}</ref>  Importantly, gap junction channels are found between cochlear supporting cells, but not auditory [[hair cells]].<ref>{{Cite journal | doi = 10.1007/BF00186783 | last1 = Kikuchi | first1 = T. | last2 = Kimura | first2 = R. S. | last3 = Paul | first3 = D. L. | last4 = Adams | first4 = J. C. | title = Gap junctions in the rat cochlea: Immunohistochemical and ultrastructural analysis | journal = Anatomy and Embryology | volume = 191 | issue = 2 | pages = 101–118 | year = 1995 | pmid = 7726389| s2cid = 24900775 }}</ref>

==Clinical significance==
{{expand section|date=September 2015}}

=== Physical damage ===
Damage to the cochlea can result from different incidents or conditions like a severe head injury, a [[cholesteatoma]], an infection, and/or exposure to loud noise which could kill hair cells in the cochlea.

=== Hearing loss ===
{{main|Hearing loss}} {{further|Cochlear implant}}
Hearing loss associated with the cochlea is often a result of outer hair cells and inner hair cells damage or death. Outer hair cells are more susceptible to damage, which can result in less sensitivity to weak sounds. Frequency sensitivity is also affected by cochlear damage which can impair the patient's  ability to distinguish between spectral differences of vowels. The effects of cochlear damage on different aspects of hearing loss like temporal integration, pitch perception, and frequency determination are still being studied, given that multiple factors must be taken into account in regard to cochlear research.<ref>{{Cite journal |last=Moore |first=Brian C. J. |date=April 1996 |title=Perceptual Consequences of Cochlear Hearing Loss and their Implications for the Design of Hearing Aids |url=http://journals.lww.com/00003446-199604000-00007 |journal=Ear and Hearing |language=en |volume=17 |issue=2 |pages=133–161 |doi=10.1097/00003446-199604000-00007 |pmid=8698160 |issn=0196-0202|url-access=subscription }}</ref>

===Bionics===
In 2009, engineers at the [[Massachusetts Institute of Technology]] created an [[Integrated circuit|electronic chip]] that can quickly analyze a very large range of [[Radio frequency|radio frequencies]] while using only a fraction of the power needed for existing technologies; its design specifically mimics a cochlea.<ref>{{cite web | url = http://web.mit.edu/newsoffice/2009/bio-electronics-0603.html | title = Drawing inspiration from nature to build a better radio: New radio chip mimics human ear, could enable universal radio | author = Anne Trafton | publisher = MIT newsoffice | date = June 3, 2009}}</ref><ref>{{cite journal |author1=Soumyajit Mandal |author2=Serhii M. Zhak |author3=Rahul Sarpeshkar | title = A Bio-Inspired Active Radio-Frequency Silicon Cochlea | journal = IEEE Journal of Solid-State Circuits | volume = 44 | issue = 6 | date = June 2009 | pages = 1814–1828 | doi = 10.1109/JSSC.2009.2020465|bibcode=2009IJSSC..44.1814M | url = https://dspace.mit.edu/bitstream/1721.1/59982/2/Mandal-2009-A%20Bio-Inspired%20Active%20Radio-Frequency%20Silicon%20Cochlea.pdf |hdl=1721.1/59982 |s2cid=10756707 | hdl-access = free }}</ref>

==Other animals==
The coiled form of cochlea is unique to [[mammal]]s. In birds and in other non-mammalian [[vertebrate]]s, the compartment containing the sensory cells for hearing is occasionally also called "cochlea," despite not being coiled up. Instead, it forms a blind-ended tube, also called the cochlear duct. This difference apparently [[Evolution of the cochlea#Evolutionary perspective|evolved]] in parallel with the differences in '''frequency range of hearing''' between mammals and non-mammalian vertebrates. The superior '''frequency range''' in mammals is partly due to their unique mechanism of pre-amplification of sound by active cell-body vibrations of outer [[hair cells]]. Frequency resolution is, however, not better in mammals than in most lizards and birds, but the upper frequency limit is – sometimes much – higher. Most bird species do not hear above 4&ndash;5&nbsp;kHz, the currently known maximum being ~ 11&nbsp;kHz in the barn owl. Some marine mammals hear up to 200&nbsp;kHz. A long coiled compartment, rather than a short and straight one, provides more space for additional octaves of hearing range, and has made possible some of the highly derived behaviors involving mammalian hearing.<ref>{{Cite book |last1=Vater |first1=Marianne |url=http://link.springer.com/10.1007/978-1-4419-8957-4_9 |title=Hearing Organ Evolution and Specialization: Early and Later Mammals |last2=Meng |first2=Jin |last3=Fox |first3=Richard C. |date=2004 |publisher=Springer New York |isbn=978-0-387-21093-3 |editor-last=Manley |editor-first=Geoffrey A. |volume=22 |location=New York, NY |pages=256–288 |doi=10.1007/978-1-4419-8957-4_9 |editor-last2=Fay |editor-first2=Richard R. |editor-last3=Popper |editor-first3=Arthur N.}}</ref>

As the study of the cochlea should fundamentally be focused at the level of hair cells, it is important to note the anatomical and physiological differences between the hair cells of various species.  In birds, for instance, instead of outer and inner hair cells, there are tall and short hair cells.  There are several similarities of note in regard to this comparative data.  For one, the tall hair cell is very similar in function to that of the inner hair cell, and the short hair cell, lacking afferent auditory-nerve fiber innervation, resembles the outer hair cell.  One unavoidable difference, however, is that while all hair cells are attached to a [[tectorial membrane]] in birds, only the outer hair cells are attached to the tectorial membrane in mammals.

==Gallery==

<gallery>
File:Right osseous labyrinth svg hariadhi.svg|Right osseous labyrinth. Lateral view.
File:Right_osseous_labyrinth_interior_svg_hariadhi.svg|Interior of right osseous labyrinth.
File:Gray923.png|The cochlea and vestibule, viewed from above.
File:Gray928.png|Cross-section of the cochlea.
</gallery>

==See also==
{{Anatomy-terms}}
* [[Bony labyrinth]]
* [[Membranous labyrinth]]
* [[Cochlear implant]]
* [[Cochlear nerve]]
* [[Cochlear nuclei]]
* [[Evolution of the cochlea]]
* [[Noise health effects]]
* [[Hearing]]

==References==
{{Reflist}}

==Further reading==
*{{cite book |url=https://books.google.com/books?id=gwYJAAAACAAJ |title=The Cochlea |first1=Peter |last1=Dallos |first2=Arthur N. |last2=Popper |first3=Richard R. |last3=Fay }}
*{{cite book |url=https://books.google.com/books?id=JxJVte3xW2cC |title=Audition |first1=Michel |last1=Imbert |first2=R. H. |last2=Kay |year=1992 |publisher=MIT Press |isbn=9780262023313 }}
*{{cite book |url=https://books.google.com/books?id=giFuKH5u7O0C |title=Physiology of the Ear |first1=Anthony F. |last1=Jahn |first2=Joseph |last2=Santos-Sacchi |year=2001 |publisher=Singular/Thomson Learning |isbn=9781565939943 }}
*{{cite book |url=https://books.google.com/books?id=H_j6v1Nt044C |title=Audiology |first1=Ross J. |last1=Roeser |first2=Michael |last2=Valente |first3=Holly |last3=Hosford-Dunn |year=2007 |publisher=Thieme |isbn=9781588905420 }}

==External links==
* {{MeshName|Cochlea}}
* [http://www.cochlea.org/ "Promenade 'Round the Cochlea"] by R. Pujol, S. Blatrix, T. Pujol et al. at [[University of Montpellier]]
* [https://www.kasem.info/histology-videos/second-year-histology-videos/the-ear-histology-videos "Histology Videos of The Ear"]

{{Auditory system}}
{{Authority control}}

[[Category:Auditory system]]
[[Category:Otology]]
[[Category:Audiology]]
[[Category:Otorhinolaryngology]]
[[Category:Human head and neck]]
[[Category:Skull]]
[[Category:Ear]]
[[Category:Inner ear]]
[[Category:Bones of the head and neck]]
[[Category:Hearing]]
[[Category:Articles containing video clips]]