View source for Organ of Corti

{{short description|Receptor organ for hearing}}
{{More citations needed|date=December 2014}}
{{Infobox anatomy
| Name        = Organ of Corti
| Latin       = organum spirale
| Greek       = 
| Image       = Cochlea-crosssection.svg
| Caption     = A cross section of the cochlea illustrating the organ of Corti
| Width       = 300
| Image2      = 
| Caption2    = Section through the spiral organ of Corti (magnified)
| Precursor   = 
| System      = 
| Artery      = 
| Vein        = 
| Nerve       = 
| Lymph       = 
| PartOf      = [[Cochlea]] of the [[inner ear]]
}}
The '''organ of Corti''', or '''spiral organ''', is the receptor organ for hearing and is located in the mammalian [[cochlea]]. This highly varied strip of [[epithelium|epithelial cells]] allows for transduction of auditory signals into nerve impulses' [[action potential]].<ref name=Hudspeth2014>{{cite journal|last=Hudspeth|first=A|title= Integrating the active process of hair cells with cochlear function|journal= Nature Reviews Neuroscience|date=2014|volume=15|issue=9|pages=600–614|pmid=25096182|doi=10.1038/nrn3786 |s2cid=3716179}}</ref> Transduction occurs through vibrations of structures in the inner ear causing displacement of cochlear fluid and movement of [[hair cell]]s at the organ of Corti to produce electrochemical signals.<ref name=Pujol2013>[http://www.cochlea.org/en/hearing/ear The Ear] {{Webarchive|url=https://web.archive.org/web/20181008090116/http://www.cochlea.org/en/hearing/ear |date=2018-10-08 }} Pujol, R., Irving, S., 2013</ref>

Italian anatomist [[Alfonso Giacomo Gaspare Corti]] (1822–1876) discovered the organ of Corti in 1851.<ref name=Betlejewski2008>{{cite journal|last=Betlejewski|first=S|title= Science and life – the history of Marquis Alfonso Corti|journal= Otolaryngologia Polska|date=2008|volume=62|issue=3|pages=344–347|pmid=18652163|doi=10.1016/S0030-6657(08)70268-3 }}</ref> The structure evolved from the [[basilar papilla]] and is crucial for [[mechanotransduction]] in mammals.

==Structure==
[[File:Organ of corti.svg|thumb|Cross-section through the spiral organ of Corti at greater magnification, showing position of the hair cells on the basement membrane.]]

The organ of Corti is located in the [[scala media]] of the [[cochlea]] of the [[inner ear]] between the [[vestibular duct]] and the [[tympanic duct]] and is composed of mechanosensory cells, known as [[hair cell]]s.<ref name=Pujol2013/> Strategically positioned on the [[basilar membrane]] of the organ of Corti are three rows of [[hair cell#Outer hair cells – acoustical pre-amplifiers|outer hair cells]] (OHCs) and one row of [[hair cell#Inner hair cells – from sound to nerve signal|inner hair cells]] (IHCs).<ref name=Malgrange2002>{{cite journal|last=Malgrange|first=B|author2=Van de Water, T.R|author3=Nguyen, L|author4=Moonen, G|author5=Lefebvre, P.P|title= Epithelial supporting cells can differentiate into outer hair cells and Deiters' cells in the cultured organ of Corti|journal=Cellular and Molecular Life Sciences|date=2002|volume=59|issue=10|pages=1744–1757|pmid=12475185|doi=10.1007/pl00012502|s2cid=2962483|pmc=11337542}}</ref> Surrounding these hair cells are supporting cells: [[Deiters cell]]s, also called [[phalangeal cell]]s, which have a close relation with the OHCs, and pillar cells, which separate and support both the OHCs and the IHCs.<ref name=Malgrange2002 />

Projecting from the tops of the hair cells are tiny finger-like projections called [[stereocilia]], which are arranged in a graduated fashion with the shortest stereocilia on the outer rows and the longest in the center. This gradation is thought to be the most important anatomic feature of the organ of Corti because this allows the sensory cells superior tuning capability.<ref name=Lim1986>{{cite journal|last=Lim|first=D|title= Functional structure of the organ of Corti: a review|journal= Hearing Research|date=1986|volume=22|issue=1–3|pages=117–146|pmid=3525482|doi=10.1016/0378-5955(86)90089-4|s2cid=4764624}}</ref>

If the cochlea were uncoiled, it would roll out to be about 33&nbsp;mm long in women and 34 mm in men, with about 2.28&nbsp;mm of standard deviation for the population.<ref>{{Cite journal | pmid = 17471760| year = 2007| last1 = Miller| first1 = J. D.| title = Sex differences in the length of the organ of Corti in humans| journal = The Journal of the Acoustical Society of America| volume = 121| issue = 4| pages = EL151-5 | doi=10.1121/1.2710746| bibcode = 2007ASAJ..121L.151M| doi-access = free}}</ref> The cochlea is also tonotopically organized, meaning that different frequencies of sound waves interact with different locations on the structure. The base of the cochlea, closest to the outer ear, is the most stiff and narrow and is where the high-frequency sounds are transduced. The apex, or top, of the cochlea is wider and much more flexible and loose and functions as the transduction site for low-frequency sounds.<ref name=Fritzsch2012>{{cite journal|last=Fritzsch|first=B|date=2012|title=Dissecting the molecular basis of organ of Corti development: where are we now?|journal=Hearing Research|volume=276|issue=1–2|pages=16–26|doi=10.1016/j.heares.2011.01.007|pmid=21256948|author2=Jahan, I|author3=Pan, N|author4=Kers, J|author5=Duncan, J|author6=Kopecky, B|pmc=3097286}}</ref>

==Function==
[[File:Anatomy of the Human Ear.svg|thumb|Image showing the [[outer ear]], [[middle ear]], and [[inner ear]], and how sound is conducted through the outer ear, to the [[ossicles]] of the middle ear, through to the inner ear and the cochlea, where the organ of Corti sits.]]
The function of the organ of Corti is to convert ([[signal transduction|transduce]]) sounds into electrical signals that can be transmitted to the brainstem through the auditory nerve.<ref name=Pujol2013/> It is the [[auricle (anatomy)|auricle]] and [[middle ear]] that act as mechanical transformers and amplifiers so that the sound waves end up with amplitudes 22 times greater than when they entered the ear.

=== Auditory transduction ===
In normal hearing, the majority of the auditory signals that reach the organ of Corti in the first place come from the outer ear. [[Sound waves]] enter through the [[auditory canal]] and vibrate the [[tympanic membrane]], also known as the eardrum, which vibrates three small bones called the [[ossicles]]. As a result, the attached [[oval window]] moves and causes movement of the [[round window]], which leads to displacement of the cochlear fluid.<ref name=NB>{{cite book|author=Nichols, J.G|author2=Martin, A.R.|author3=Fuchs, P.A|author4=Brown, D.A|author5=Diamond, M.E|author6=Weisblat, D.A|year=2012 |title=From Neuron to Brain, 5th Edition|publisher=Sinauer Associates, Inc|location= Sunderland, MA|pages= 456–459|isbn= 978-0-87893-609-0 }}</ref>
However, the stimulation can happen also via direct vibration of the cochlea from the skull. The latter is referred to as Bone Conduction (or BC) hearing, as complementary to the first one described, which is instead called Air Conduction (or AC) hearing. Both AC and BC stimulate the basilar membrane in the same way (Békésy, G.v., Experiments in Hearing. 1960).

The basilar membrane on the tympanic duct presses against the hair cells of the organ as [[perilymph]]atic pressure waves pass. The stereocilia atop the IHCs move with this fluid displacement and in response their [[cation]], or positive ion selective, channels are pulled open by [[cadherin]] structures called [[stereocilia (inner ear)#Morphology|tip links]] that connect adjacent stereocilia.<ref>{{Cite journal|last1=Müller|first1=Ulrich|last2=Gillespie|first2=Peter G.|last3=Williams|first3=David S.|last4=Reynolds|first4=Anna|last5=Dumont|first5=Rachel A.|last6=Lillo|first6=Concepcion|last7=Siemens|first7=Jan|date=April 2004|title=Cadherin 23 is a component of the tip link in hair-cell stereocilia|journal=Nature|volume=428|issue=6986|pages=950–955|doi=10.1038/nature02483|pmid=15057245|bibcode=2004Natur.428..950S|s2cid=3506274|issn=1476-4687}}</ref> The organ of Corti, surrounded in potassium-rich fluid [[endolymph]], lies on the [[basilar membrane]] at the base of the [[scala media]]. Under the organ of Corti is the [[scala tympani]] and above it, the [[scala vestibuli]]. Both structures exist in a low potassium fluid called [[perilymph]].<ref name=NB /> Because those stereocilia are in the midst of a high concentration of potassium, once their cation channels are pulled open, potassium ions as well as calcium ions flow into the top of the hair cell. With this influx of positive ions the IHC becomes [[depolarization|depolarized]], opening voltage-gated calcium channels at the basolateral region of the hair cells and triggering the release of the neurotransmitter [[glutamate]]. An electrical signal is then sent through the [[auditory nerve]] and into the [[auditory cortex]] of the brain as a neural message.

=== Cochlear amplification ===
{{Further|Cochlear amplifier}}
The organ of Corti is also capable of modulating the auditory signal.<ref name=Fritzsch2012/> The outer hair cells (OHCs) can amplify the signal through a process called [[electromotility]] where they increase movement of the basilar and tectorial membranes and therefore increase deflection of stereocilia in the IHCs.<ref name=NB /><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]]|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|author-link=Jonathan Ashmore|date=2008|title=Cochlear Outer Hair Cell Motility|journal=[[Physiological Reviews]]|volume=88|issue=1|pages=173–210|doi=10.1152/physrev.00044.2006|issn=0031-9333|pmid= 18195086|s2cid=17722638}} {{open access}}</ref>

A crucial piece to this [[cochlear amplifier|cochlear amplification]] is the motor protein [[prestin]], which changes shape based on the voltage potential inside of the hair cell. When the cell is depolarized, prestin shortens, and because it is located on the membrane of OHCs it then pulls on the basilar membrane and increasing how much the membrane is deflected, creating a more intense effect on the inner hair cells (IHCs). When the cell hyperpolarizes prestin lengthens and eases tension on the IHCs, which decreases the neural impulses to the brain. In this way, the hair cell itself is able to modify the auditory signal before it even reaches the brain.

==Development==
The organ of Corti, in between the [[scala tympani]] and the [[scala media]], develops after the formation and growth of the [[cochlear duct]].<ref name=Fritzsch2012 /> The inner and outer hair cells then differentiate into their appropriate positions and are followed by the organization of the supporting cells. The topology of the supporting cells lends itself to the actual mechanical properties that are needed for the highly specialized sound-induced movements within the organ of Corti.<ref name=Fritzsch2012 />

Development and growth of the organ of Corti relies on specific genes, many of which have been identified in previous research ([[SOX2]], [[GATA3]], [[EYA1]], [[FOXG1]], [[BMP4]], [[RAC1]], and more),<ref name=Fritzsch2012 /> to undergo such differentiation. Specifically, the cochlear duct growth and the formation of hair cells within the organ of Corti.

Mutations in the genes expressed in or near the organ of Corti before the differentiation of hair cells will result in a disruption in the differentiation, and potential malfunction of, the organ of Corti.

==Clinical significance==

=== Hearing loss ===
{{Main|Hearing impairment}}
The organ of Corti can be damaged by excessive sound levels, leading to [[Noise health effects|noise-induced impairment]].<ref>{{Cite journal|last=Lim|first=David J.|date=March 1986|title=Effects of noise and ototoxic drugs at the cellular level in the cochlea: A review|journal=American Journal of Otolaryngology|volume=7|issue=2|pages=73–99|doi=10.1016/S0196-0709(86)80037-0|pmid=3515985}}</ref>

The most common kind of hearing impairment, [[sensorineural hearing loss]], includes as one major cause the reduction of function in the organ of Corti.  Specifically, the active amplification function of the [[outer hair cell]]s is very sensitive to damage from exposure to trauma from overly-loud sounds or to certain [[Ototoxicity|ototoxic]] drugs.  Once outer hair cells are damaged, they do not regenerate, and the result is a loss of sensitivity and an abnormally large growth of loudness (known as ''recruitment'') in the part of the spectrum that the damaged cells serve.<ref>{{cite book | title = Medical-Legal Evaluation of Hearing Loss | author = Robert A. Dobie | url = https://books.google.com/books?id=7dLVJDTUfdAC&q=%22outer+hair+cells%22+%22organ+of+corti%22+%22hearing+loss%22&pg=PA27 | publisher = Thomson Delmar Learning | year = 2001 | isbn = 0-7693-0052-9 }}</ref>

While hearing loss has always been considered irreversible in mammals, fish and birds routinely repair such damage. A 2013 study has shown that the use of particular drugs may reactivate genes normally expressed only during hair cell development. The research was carried out at [[Harvard Medical School]], [[Massachusetts Eye and Ear]], and the [[Keio University]] School of Medicine in Japan.<ref>{{cite web|url=http://beyondthedish.wordpress.com/tag/cochlear-hair-cells/|title=Cochlear hair cells - Beyond the Dish|work=wordpress.com}}</ref><ref>{{Cite journal |last1=Askew |first1=Charles |last2=Rochat |first2=Cylia |last3=Pan |first3=Bifeng |last4=Asai |first4=Yukako |last5=Ahmed |first5=Hena |last6=Child |first6=Erin |last7=Schneider |first7=Bernard L. |last8=Aebischer |first8=Patrick |last9=Holt |first9=Jeffrey R. |date=8 July 2015 |title=Tmc gene therapy restores auditory function in deaf mice |journal=[[Science Translational Medicine]] |language=en |volume=7 |issue=295 |page=295ra108 |doi=10.1126/scitranslmed.aab1996 |issn=1946-6234 |pmc=7298700 |pmid=26157030}}</ref>

==Additional images==
<gallery>
 File:Gray903.png|Transverse section of the cochlear duct of a fetal cat.
 File:Gray928.png|Diagrammatic longitudinal section of the cochlea
 File:Gray929.png|Floor of ductus cochlearis
 File:Gray930.png|Limbus laminæ spiralis and membrana basilaris
 File:Gray931.png|Section through the spiral organ of Corti (magnified)
</gallery>

==Notes==
{{Reflist}}

== References ==
*{{cite journal | author = Corti A | year = 1851 | title = Recherches sur l'organe de l'ouïe des mammiferes | journal = Zeitschrift für Wissenschaftliche Zoologie | volume = 3 | pages = 106–169 }}
*{{cite journal |vauthors= Fritzsch B, Jahan I, Pan N, Kersigo J, Duncan J, Kopecky B |year= 2012 |title= Dissecting the molecular basis of organ of Corti development: where are we now?|journal= Hearing Research |volume= 276 |issue= 1–2 |pages= 16–26 |doi=10.1016/j.heares.2011.01.007 |pmid=21256948 |pmc=3097286}}
History. (n.d.).
*{{cite journal | author = Hudspeth A | year = 2014 | title = Integrating the active process of hair cells with cochlear function | journal = Nature Reviews Neuroscience | volume = 15 | issue = 9| pages = 600–614 | doi=10.1038/nrn3786 | pmid=25096182| s2cid = 3716179 }}
*{{cite journal | author = Lim D | year = 1986 | title = Functional structure of the organ of Corti: a review | journal = Hearing Research | volume = 22 | issue = 1–3| pages = 117–146 | doi=10.1016/0378-5955(86)90089-4 | pmid=3525482| s2cid = 4764624 }}
*{{cite journal |vauthors= Malgrange B, Thiry M, Van de Water TR, Nguyen L, Moonen G, Lefebvre PP |year= 2002 |title= Epithelial supporting cells can differentiate into outer hair cells and Deiters' cells in the cultured organ of Corti |journal= Cellular and Molecular Life Sciences |volume= 59 |issue= 10 |pages= 1744–1757 |doi=10.1007/PL00012502 |pmid=12475185|s2cid= 2962483 |pmc= 11337542 }}
*Nicholls, J. G., Martin, A. R., Fuchs, P. A., Brown, D. A., Diamond, M. E., & Weisblat, D. A. (2012). From Neuron to Brain (5th ed., pp.&nbsp;456–459). Sunderland, MA: Sinauer Associates, Inc.
*Pritchard U. "On the organ of Corti in mammals". 2 March 1876, ''[[Proceedings of the Royal Society of London]]'', volume 24, pp.&nbsp;346–52 {{OCLC|1778190}}
*Pujol, R., & Irving, S. (2013). The Ear.

==External links==
{{Commons category|Organ of Corti}}
*[https://www.youtube.com/watch?v=1JE8WduJKV4 Organ of Corti 3D animation]
* http://lobe.ibme.utoronto.ca/presentations/OHC_Electromotility/sld005.htm {{Webarchive|url=https://web.archive.org/web/20050330181655/http://lobe.ibme.utoronto.ca/presentations/OHC_Electromotility/sld005.htm |date=2005-03-30 }} Diagram at University of Toronto
* http://mayoresearch.mayo.edu/mayo/research/ent_research/images/image02.gif {{Webarchive|url=https://web.archive.org/web/20070305105000/http://mayoresearch.mayo.edu/mayo/research/ent_research/images/image02.gif |date=2007-03-05 }} Diagram at Mayo
* http://www.iurc.montp.inserm.fr/cric51/audition/english/corti/fcorti.htm {{Webarchive|url=https://web.archive.org/web/20061130222722/http://www.iurc.montp.inserm.fr/cric51/audition/english/corti/fcorti.htm |date=2006-11-30 }} at University of Montpellier 1

== See also ==

* [[Hearing]]
* [[Inner ear]]
* [[List of distinct cell types in the adult human body]]

{{Auditory and vestibular anatomy}}
{{Authority control}}

[[Category:Auditory system]]
[[Category:Ear]]
[[Category:Otology]]
[[Category:Audiology]]