Changes: Organ of Corti

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Organ of Corti

A cross section of the cochlea illustrating the organ of Corti.
Latin	organum spirale
Gray's	subject #232 1056
System
MeSH	A09.246.631.246.577

Section through the spiral organ of Corti. Magnified.

Main article: Cochlea

The organ of Corti, found only in mammals, is part of the cochlea of the inner ear and is provided with hair cells or auditory sensory cells. ^[1] It evolved from the basilar papilla found in all tetrapods, except for a few derived species that have lost it. ^[2] .

Structure and function

The organ of Corti has highly specialized structures that respond to fluid-borne vibrations in the cochlea with a shearing vector in the hairs of some cochlear hair cells. It contains between 15,000-20,000 auditory nerve receptors. Each receptor has its own hair cell. The shear on the hairs opens non-selective transduction ion channels that are permeable to potassium and calcium, leading to hair cell plasma membrane depolarization, activation of voltage-dependent calcium channels at the synaptic basolateral pole of the cells which triggers vesicle exocytosis and liberation of glutamate neurotransmitter to the synaptic cleft and electrical signaling to the auditory cortex via spiral ganglion neurons. The pinna and middle ear act as mechanical transformers and amplifiers, so that by the time sound waves reach the organ of Corti, their pressure amplitude is 22 times that of the air impinging on the pinna. The organ of Corti can be damaged by excessive sound levels, leading to noise-induced health effects. The organ of Corti is the structure that transduces pressure waves to action potentials. The organ of Corti sits inside the cochlear duct, between the scala vestibuli and the scala tympani. The basilar membrane on the scala tympani presses against the hair cells of the organ as perilymphatic pressure waves pass.

The discoverer: Alfonso Corti

The organ was named after the Italian anatomist Marquis Alfonso Giacomo Gaspare Corti (1822-1876), who conducted microscopic research of the mammalian auditory system from 1849 to 1851 at the Koelliker laboratory in Würzburg (Germany). He developed new coloring techniques in microscopic anatomy, which enabled him to distinguish and describe individual components inside the highly complex cochlea that had previously been unidentified. In 1851 he was the first to describe the core sensory organ in the mammalian cochlea, the organ of Corti.

Hearing loss

Main article: Hearing impairment

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 cells is very sensitive to damage from exposure to trauma from overly-loud sounds or to certain 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.^[3]

While hearing loss has always been considered irreversible in mammals, fish and birds routinely repair such damage. A recent 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, the Massachusetts Eye and Ear Infirmary, and the Keio University School of Medicine in Japan.^[4]

Additional images

References

↑ Definition of Organ of Corti - Merriam Webster - Retrieved 30 April 2012.
↑ Dissecting the molecular basis of organ of Corti development
↑ Robert A. Dobie (2001). Medical-Legal Evaluation of Hearing Loss, Thomson Delmar Learning.
↑ Drug Induces Hearing Restoration in Rodents

External links

http://lobe.ibme.utoronto.ca/presentations/OHC_Electromotility/sld005.htm Diagram at University of Toronto
http://mayoresearch.mayo.edu/mayo/research/ent_research/images/image02.gif Diagram at Mayo
http://www.iurc.montp.inserm.fr/cric51/audition/english/corti/fcorti.htm at University of Montpellier 1

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de:Cortisches Organ es:Órgano de Corti pt:Órgão de Corti ru:Корти, Альфонсо

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[1] Definition of Organ of Corti - Merriam Webster - Retrieved 30 April 2012.

[2] Dissecting the molecular basis of organ of Corti development

[3] Robert A. Dobie (2001). Medical-Legal Evaluation of Hearing Loss, Thomson Delmar Learning.

[4] Drug Induces Hearing Restoration in Rodents

[1]

[2]

[3]

[4]

@@ Line 20: / Line 20: @@
+The '''organ of Corti''', found only in [[mammal]]s, is part of the [[cochlea]] of the [[inner ear]] and is provided with [[hair cell]]s or auditory sensory cells. <ref>[http://www.merriam-webster.com/medical/organ%20of%20corti Definition of Organ of Corti] - ''Merriam Webster'' - Retrieved 30 April 2012.</ref> It evolved from the [[basilar papilla]] found in all [[tetrapods]], except for a few derived species that have lost it. <ref>[http://pubmedcentralcanada.ca/pmcc/articles/PMC3097286/ Dissecting the molecular basis of organ of Corti development]</ref> .
-The '''organ of Corti''' (or '''spiral organ''') is the organ in the [[inner ear]] of [[mammal]]s that contains auditory sensory cells, or "[[hair cell]]s".
 ==Structure and function==
-It has highly specialized structures that respond to fluid-borne vibrations in the [[cochlea]] with a shearing vector in the hairs of some cochlear hair cells. The Organ of Corti contains between 15,000-20,000 auditory nerve recepetors. Each receptor has its own hair cell. The shear on the hairs opens [[ion channel]]s, leading to neural, electrical signaling to the [[auditory cortex]].  The [[pinna]] and [[middle ear]] amplify sound levels, so that by the time these longitudinal waves reach the Organ of Corti, they are 20 times that of the levels impinging on the pinna.  This amplification is partly responsible for the delicacy of the Organ of Corti with respect to excessive sound levels, and helps to understand [[noise health effects|noise induced health effects]].
+The organ of Corti has highly specialized structures that respond to fluid-borne vibrations in the [[cochlea]] with a shearing vector in the hairs of some cochlear hair cells. It contains between 15,000-20,000 auditory nerve receptors. Each receptor has its own hair cell. The shear on the hairs opens non-selective transduction [[ion channel]]s that are permeable to potassium and calcium, leading to hair cell plasma membrane depolarization, activation of voltage-dependent calcium channels at the synaptic basolateral pole of the cells which triggers vesicle exocytosis and liberation of glutamate neurotransmitter to the synaptic cleft and electrical signaling to the [[auditory cortex]] via spiral ganglion neurons.  The [[pinna (anatomy)|pinna]] and [[middle ear]] act as mechanical transformers and amplifiers, so that by the time sound waves reach the organ of Corti, their pressure amplitude is 22 times that of the air impinging on the pinna.  The organ of Corti can be damaged by excessive sound levels, leading to [[noise health effects|noise-induced health effects]]. The organ of Corti is the structure that transduces pressure waves to action potentials. The organ of Corti sits inside the cochlear duct, between the scala vestibuli and the scala tympani. The basilar membrane on the scala tympani presses against the hair cells of the organ as perilymphatic pressure waves pass.
 ==The discoverer: Alfonso Corti==
-The organ was named after the Italian anatomist Marquis Alfonso Giacomo Gaspare Corti (1822-1876), who conducted microscopic research of the mammalian auditory system from 1849 to 1851 at the Koelliker laboratory in Würzburg (Germany). He developed new coloring techniques in microscopic anatomy, which enabled him to distinguish and describe individual components inside the highly complex cochlea that had previously been unidentified. In 1851 he was the first to describe the core sensory organ in the mammalian cochlea, the organ of Corti.
+The organ was named after the Italian anatomist Marquis [[Alfonso Giacomo Gaspare Corti]] (1822-1876), who conducted microscopic research of the mammalian [[auditory system]] from 1849 to 1851 at the Koelliker laboratory in Würzburg (Germany). He developed new coloring techniques in microscopic anatomy, which enabled him to distinguish and describe individual components inside the highly complex cochlea that had previously been unidentified. In 1851 he was the first to describe the core sensory organ in the mammalian cochlea, the organ of Corti.
-==Hearing Loss==
+==Hearing loss==
-As stated in the <i>Modern Biology</i> textbook, "Different pitches stimulate different parts of the cochlea. Normally, the human ear can detect sounds ranging from 16 to 20,000 [[hertz|cycles]] per second. The hair cells that line the cochlea are a delicate and vulnerable part of the ear. Repeated or sustained exposure to loud noise destroys the neurons of the Organ of Corti. Once destroyed, the hair cells are not replaced, and the sound [[frequency|frequencies]] interpreted by them are no longer heard. Hair cells that respond to high frequency sound are very vulnerable to destruction, and loss of these neurons typically produces difficulty understanding human voices. Much of this type of permanent [[hearing impairment|hearing loss]] is avoidable by reducing exposure to loud noises in the environment, such as industrial and machinery noise, gunfire, and loud music."<ref>Alcamo, I. Edward, Ph.D., and others. ''Modern Biology''. Edited by Susan Feldkamp and others. Austin: Holt, Rinehart and Winston, 2002.</ref>
+{{main|Hearing impairment}}
-==Notes==
+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 = http://books.google.com/books?id=7dLVJDTUfdAC&pg=PA27&dq=%22outer+hair+cells%22+%22organ+of+corti%22+%22hearing+loss%22#PPA29,M1 | 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 recent 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]], the [[Massachusetts Eye and Ear Infirmary]], and the [[Keio University]] School of Medicine in Japan.<ref>[http://beyondthedish.wordpress.com/tag/cochlear-hair-cells/ Drug Induces Hearing Restoration in Rodents]</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>
+==See also==
+==References==
 <div class="references-small">
 <references/>
 </div>
-==References==
+==Further reading==
 *Corti A (1851) ''Recherches sur l'organe de Corti de l'ouïe des mammifères''. Z wiss Zool 3: 1-106.
+*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}}
 ==External links==
@@ Line 48: / Line 65: @@
 [[Category:Auditory system]]
-[[Category:Eponymous anatomical structures]]
+[[Category:Cochlea]]
+[[Category:Ear]]
 [[de:Cortisches Organ]]