Editing Cone cell (section)

==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>