View source for Cone cell

{{Short description|Photoreceptor cells responsible for color vision made to function in bright light}}
{{Use US English|date=January 2018}}

{{Infobox neuron
| name = Cone cells
| image= Cone-fundamentals-with-srgb-spectrum.svg
| caption = Normalized [[responsivity]] spectra of human cone cells, S, M, and L types
|location = [[Retina]] of vertebrates
|function = [[Color vision]]
|neurotransmitter =
|morphology =
|afferents =
|efferents =
}}

'''Cone cells''' or '''cones''' are [[photoreceptor cells]] in the [[retina]] of the vertebrate [[eye]]. Cones are active in daylight conditions and enable [[photopic vision]], as opposed to [[rod cell]]s, which are active in dim light and enable [[scotopic vision]]. Most vertebrates (including humans) have several classes of cones, each sensitive to a different part of the [[visible spectrum]] of [[light]]. The comparison of the responses of different cone cell classes enables [[color vision]]. There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration occurring towards the [[macula]] and most densely packed in the [[fovea centralis]], a {{val|0.3|u=mm}} diameter rod-free area with very thin, densely packed cones. Conversely, like rods, they are absent from the [[optic disc]], contributing to the [[Blind spot (vision)|blind spot]].<ref>{{cite web |title=The Rods and Cones of the Human Eye |url=http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html |website=HyperPhysics Concepts - Georgia State University}}</ref>

Cones are less sensitive to light than the [[Rod cell|rod cells]] in the retina (which support vision at low light levels), but allow the [[Visual perception|perception]] of color. They are also able to perceive finer detail and more rapid changes in images because their response times to [[Stimulus (physiology)#Vision|stimuli]] are faster than those of rods.<ref name="Kandel">{{cite book
| first = E.R.
| last = Kandel
|author2=Schwartz, J.H |author3=Jessell, T. M.
| year = 2000
| title = Principles of Neural Science
| url = https://archive.org/details/isbn_9780838577011
| url-access = registration
| edition = 4th
| pages = [https://archive.org/details/isbn_9780838577011/page/507 507–513]
| publisher = McGraw-Hill
| location = New York
| isbn = 9780838577011
}}</ref> In humans, cones are normally one of three types: S-cones, M-cones and L-cones, with each type bearing a different [[Opsin#Vertebrate_visual_opsins|opsin]]: [[OPN1SW]], [[OPN1MW]], and [[OPN1LW]] respectively. These cones are sensitive to visible wavelengths of light that correspond to short-wavelength, medium-wavelength and longer-wavelength light respectively.<ref>Schacter, Gilbert, Wegner, "Psychology", New York: Worth Publishers,2009.</ref> Because [[Human|humans]] usually have three kinds of cones with different [[photopsin]]s, which have different response curves and thus respond to variation in color in different ways, humans have [[trichromatic vision]]. Being [[color blindness|color blind]] can change this, and there have been some verified reports of people with four types of cones, giving them [[tetrachromat]]ic vision.<ref name="Jameson 2001" >
{{cite journal
|doi=10.3758/BF03196159
|author=Jameson, K. A.
|author2=Highnote, S. M.
|author3=Wasserman, L. M.
|name-list-style=amp
|year=2001
|title=Richer color experience in observers with multiple photopigment opsin genes
|journal=Psychonomic Bulletin and Review
|volume=8 |issue=2 |pages=244–261
|pmid=11495112
|s2cid=2389566
|url=https://link.springer.com/content/pdf/10.3758/BF03196159.pdf
|doi-access=free
}}<!---former link broken: http://www.klab.caltech.edu/cns186/papers/Jameson01.pdf---></ref><ref>{{cite news |date=7 March 2007 |title=You won't believe your eyes: The mysteries of sight revealed |newspaper=[[The Independent]] |url=http://news.independent.co.uk/world/science_technology/article2336163.ece |url-status=dead |access-date=22 August 2009 |archive-url=https://web.archive.org/web/20080706001354/http://news.independent.co.uk/world/science_technology/article2336163.ece |archive-date=6 July 2008 |quote=Equipped with four receptors instead of three, Mrs M - an English social worker, and the first known human "tetrachromat" - sees rare subtleties of colour.}}</ref><ref name="Roth 2006">{{cite news |author=Mark Roth |date=September 13, 2006 |title=Some women may see 100,000,000 colors, thanks to their genes |newspaper=Pittsburgh Post-Gazette |url=http://www.post-gazette.com/pg/06256/721190-114.stm |quote=A tetrachromat is a woman who can see four distinct ranges of color, instead of the three that most of us live with. |access-date=August 22, 2009 |archive-date=November 8, 2006 |archive-url=https://web.archive.org/web/20061108171635/http://www.post-gazette.com/pg/06256/721190-114.stm |url-status=dead }}</ref>
The three pigments responsible for detecting light have been shown to vary in their exact chemical composition due to [[Mutation|genetic mutation]]; different individuals will have cones with different color sensitivity.

==Structure==

===Classes===
Most vertebrates have several different classes of cone cells, differentiated primarily by the specific [[photopsin]] expressed within. The number of cone classes determines the degree of [[color vision]]. Vertebrates with one, two, three or four classes of cones possess [[monochromacy]], [[dichromacy]], [[trichromacy]] and [[tetrachromacy]], respectively.

Humans normally have three classes of cones, designated '''L''', '''M''' and '''S''' for the long, medium and short wavelengths of the visible spectrum to which they are most sensitive.<ref>{{Cite journal |last=Roorda |first=A. |last2=Williams |first2=D. R. |date=1999-02-11 |title=The arrangement of the three cone classes in the living human eye |url=https://pubmed.ncbi.nlm.nih.gov/10028967/ |journal=Nature |volume=397 |issue=6719 |pages=520–522 |doi=10.1038/17383 |issn=0028-0836 |pmid=10028967}}</ref> L cones respond most strongly to light of the longer red [[Wavelength|wavelengths]], peaking at about {{val|560|u=nm}}. M cones, respond most strongly to yellow to green medium-wavelength light, peaking at {{val|530|u=nm}}. S cones respond most strongly to blue short-wavelength light, peaking at {{val|420|u=nm}}, and make up only around 2% of the cones in the human retina. The peak wavelengths of L, M, and S cones occur in the ranges of {{val|564|-|580|u=nm}}, {{val|534|-|545|u=nm}}, and {{val|420|-|440|u=nm}} nm, respectively, depending on the individual.{{cn|date=January 2025}} The typical human photopsins are coded for by the genes [[OPN1LW]], [[OPN1MW]], and [[OPN1SW]]. The [[CIE 1931 color space]] is an often-used model of spectral sensitivities of the three cells of a typical human.<ref name="Wyszecki">{{cite book |last=Wyszecki |first=Günther |url=https://archive.org/details/colorscienceconc00unse |title=Color Science: Concepts and Methods, Quantitative Data and Formulae |author2=Stiles, W.S. |publisher=Wiley Series in Pure and Applied Optics |year=1981 |isbn=978-0-471-02106-3 |edition=2nd |location=New York |url-access=registration}}</ref><ref>{{cite book |author=R. W. G. Hunt |url=https://archive.org/details/reproductionofco0000hunt/page/11 |title=The Reproduction of Colour |publisher=Wiley–IS&T Series in Imaging Science and Technology |year=2004 |isbn=978-0-470-02425-6 |edition=6th |location=Chichester UK |pages=[https://archive.org/details/reproductionofco0000hunt/page/11 11–12] |url-access=registration}}</ref>

===Histology===
[[File:Cone cell eng.svg|thumb|The structure of a cone cell]]
Cone cells are shorter but wider than [[Rods (eye)|rod cells]]. They are typically {{val|40|-|50|u=um}} long, and their diameter varies from {{val|0.5|-|4.0|u=um}}. They are narrowest at the fovea, where they are the most tightly packed. The S cone spacing is slightly larger than the others.<ref>{{cite book | author = Brian A. Wandel | year = 1995 | title = Foundations of Vision | url = https://foundationsofvision.stanford.edu/chapter-3-the-photoreceptor-mosaic/ | access-date = 2015-07-31 | archive-url = https://web.archive.org/web/20160305155309/https://foundationsofvision.stanford.edu/chapter-3-the-photoreceptor-mosaic/ | archive-date = 2016-03-05 | url-status = dead }}</ref>

Like rods, each cone cell has a synaptic terminal, inner and outer segments, as well as an interior nucleus and various [[mitochondria]]. The synaptic terminal forms a [[synapse]] with a neuron [[bipolar cell]]. The inner and outer segments are connected by a [[cilium]].<ref name="Kandel"/> The inner segment contains [[organelle]]s and the cell's nucleus, while the outer segment contains the light-absorbing [[photopsins]], and is shaped like a [[cone]], giving the cell its name.<ref name="Kandel"/>

The outer segments of cones have invaginations of their [[cell membrane]]s that create stacks of membranous disks. [[Photopigments]] exist as [[transmembrane protein]]s within these disks, which provide more surface area for light to affect the pigments. In cones, these disks are attached to the outer membrane, whereas they are pinched off and exist separately in rods. Neither rods nor cones divide, but their membranous disks wear out and are worn off at the end of the outer segment, to be consumed and recycled by [[phagocytosis|phagocytic]] cells.

===Distribution===
[[File:ConeMosaics.jpg|thumb|250px|Illustration of the distribution of cone cells in the fovea of an individual with normal color vision (left), and a color blind (protanopic) retina. Note that the center of the fovea holds very few blue-sensitive cones.]]
[[File:Human photoreceptor distribution.svg|thumb|250px|Distribution of rods and cones along a line passing through the fovea and the blind spot of a human eye<ref>[https://foundationsofvision.stanford.edu/chapter-3-the-photoreceptor-mosaic Foundations of Vision], Brian A. Wandell</ref>]]
While rods outnumber cones in most parts of the retina, the [[Fovea centralis|fovea]], responsible for sharp central vision, consists almost entirely of cones. The distribution of photoreceptors in the retina is called the [[retinal mosaic]], which can be determined using [[photobleaching]]. This is done by exposing dark-adapted retina to a certain wavelength of light that paralyzes the particular type of cone sensitive to that wavelength for up to thirty minutes from being able to dark-adapt, making it appear white in contrast to the grey dark-adapted cones when a picture of the retina is taken. The results illustrate that '''S''' cones are randomly placed and appear much less frequently than the '''M''' and '''L''' cones. The ratio of '''M''' and '''L''' cones varies greatly among different people with regular vision (e.g. values of 75.8% '''L''' with 20.0% '''M''' versus 50.6% '''L''' with 44.2% '''M''' in two male subjects).<ref>{{cite journal | author = Roorda A. | author2 = Williams D.R. | year = 1999 | title = The arrangement of the three cone classes in the living human eye | journal = Nature | volume = 397 | issue = 6719| pages = 520–522 | pmid=10028967 | doi = 10.1038/17383 | bibcode = 1999Natur.397..520R | s2cid = 4432043 }}</ref>

==Function==
[[File:BirdCone.png|thumb|left|[[Bird vision|Bird]], [[reptile|reptilian]], and [[monotreme]] cone cells]]

The difference in the signals received from the three cone types allows the brain to perceive a continuous range of colors through the [[opponent process]] of color vision. [[Rod cells]] have a peak sensitivity at {{val|498|u=nm}}, roughly halfway between the peak sensitivities of the S and M cones.

All of the receptors contain the protein [[photopsin]]. Variations in its conformation cause differences in the optimum wavelengths absorbed.

The color yellow, for example, is perceived when the L cones are stimulated slightly more than the M cones, and the color red is perceived when the L cones are stimulated significantly more than the M cones. Similarly, blue and violet hues are perceived when the S receptor is stimulated more. S Cones are most sensitive to light at wavelengths around {{val|420|u=nm}}. At moderate to bright light levels where the cones function, the eye is more sensitive to yellowish-green light than other colors because this stimulates the two most common (M and L) of the three kinds of cones almost equally. At lower light levels, where only the rod cells function, the sensitivity is greatest at a blueish-green wavelength.

Cones also tend to possess a significantly elevated visual acuity because each cone cell has a lone connection to the optic nerve, therefore, the cones have an easier time telling that two stimuli are isolated. Separate connectivity is established in the
[[inner plexiform layer]] so that each connection is parallel.<ref name="pmid20362067">{{cite journal|last=Strettoi|first=E|author2=Novelli, E |author3=Mazzoni, F |author4=Barone, I |author5= Damiani, D |title=Complexity of retinal cone bipolar cells.|journal=Progress in Retinal and Eye Research|date=Jul 2010|volume=29|issue=4|pages=272–83|doi=10.1016/j.preteyeres.2010.03.005|pmid=20362067|pmc=2878852}}</ref>

The response of cone cells to light is also directionally nonuniform, peaking at a direction that receives light from the center of the pupil; this effect is known as the [[Stiles–Crawford effect]].

S cones may play a role in the regulation of the [[Circadian rhythm|circadian system]] and the secretion of [[melatonin]], but this role is not clear yet. Any potential role of the S cones in the circadian system would be secondary to the better established role of [[melanopsin]] (see also [[Intrinsically photosensitive retinal ganglion cell]]).<ref>{{Cite web |last=Soca |first=R |date=Feb 13, 2021 |title=S-cones and the circadian system |url=https://keldik.com/blogs/sleep-circadian-binnacle/s-cones-and-the-circadian-system |url-status=live |archive-url=https://web.archive.org/web/20210214035406/https://keldik.com/blogs/sleep-circadian-binnacle/s-cones-and-the-circadian-system |archive-date=2021-02-14 |access-date= |website=Keldik}}</ref> 

=== Color afterimage ===
Sensitivity to a prolonged stimulation tends to decline over time, leading to [[neural adaptation]]. An interesting effect occurs when staring at a particular color for a minute or so. Such action leads to an exhaustion of the cone cells that respond to that color – resulting in the [[afterimage]]. This vivid color aftereffect can last for a minute or more.<ref>Schacter, Daniel L. ''Psychology: the second edition.'' Chapter 4.9.</ref>

==Associated diseases==
* [[Achromatopsia]] (rod [[monochromacy]]){{dash}}a form of [[monochromacy]] with no functional cones
* [[Blue cone monochromacy]]{{dash}}a rare form of monochromacy with only functional S-cones
* [[Congenital red–green color blindness]]{{dash}}partial color blindness where either one cone class is absent ([[dichromacy]], including [[protanopia]], [[deuteranopia]] & [[tritanopia]]) or the spectral sensitivity of one cone class is shifted ([[anomalous trichromacy]], including [[protanomaly]], [[deuteranomaly]])
* Oligocone trichromacy{{dash}}poor visual acuity and impairment of cone function according to [[Electroretinography|ERG]], but without significant color vision loss.<ref name="MICHAEL1">{{cite journal |last1=Aboshiha |first1=Jonathan |last2=Dubis |first2=Adam M |last3=Carroll |first3=Joseph |last4=Hardcastle |first4=Alison J |last5=Michaelides |first5=Michel |title=The cone dysfunction syndromes: Table 1 |journal=British Journal of Ophthalmology |date=January 2016 |volume=100 |issue=1 |pages=115–121 |doi=10.1136/bjophthalmol-2014-306505|pmid=25770143 |pmc=4717370 |doi-access=free }}</ref>
* [[Bradyopsia]]{{dash}}[[photopic vision|photopic vision has defects in detecting rapid changes in light]] .<ref name="MICHAEL1"/>
* Bornholm eye disease{{dash}}X-linked recessive [[myopia]], [[astigmatism]], impaired [[visual acuity]] and red–green [[dichromacy]].<ref name="MICHAEL1"/>
* [[Cone dystrophy]]{{dash}}a degenerative loss of cone cells
* [[Retinoblastoma]]{{dash}}a type of cancer originating from cone precursor cells

==See also==
{{col div|colwidth=30em}}
* [[Disc shedding]]
* [[Double cone (biology)|Double cones]]
* [[RG color space]]
* [[Tetrachromacy]]
* [[Melanopsin]]
* [[Color vision]]
* [[Monochromacy]]
{{colend}}[[List of distinct cell types in the adult human body]]

==References==
{{Reflist|30em}}

==External links==
* [http://ccdb.ucsd.edu/sand/main?stype=lite&keyword=cone&Submit=Go&event=display&start=1 Cell Centered Database&nbsp;– cone cell]
* [https://web.archive.org/web/20050224231545/http://webvision.umh.es/webvision/photo1.html Photoreceptors - Webvision]
* [https://www.neuinfo.org/mynif/search.php?q=Cone%20Cell&t=data&s=cover&b=0&r=20 NIF Search&nbsp;– Cone Cell] {{Webarchive|url=https://web.archive.org/web/20141216130113/https://www.neuinfo.org/mynif/search.php?q=Cone%20Cell&t=data&s=cover&b=0&r=20 |date=2014-12-16 }} via the [[Neuroscience Information Framework]]
* [https://archive.today/20130104021248/http://www.nanobotmodels.com/node/33 Model and image of cone cell]

{{Eye anatomy}}
{{Authority control}}

[[Category:Color vision]]
[[Category:Photoreceptor cells]]
[[Category:Human eye anatomy]]
[[Category:Human cells]]
[[Category:Neurons]]