Cone cell
Cone cells | |
---|---|
Details | |
Location | Retina of vertebrates |
Function | Color vision |
Identifiers | |
MeSH | D017949 |
NeuroLex ID | sao1103104164 |
TH | H3.11.08.3.01046 |
FMA | 67748 |
Anatomical terms of neuroanatomy |
Cone cells or cones are
Cones are less sensitive to light than the
The three pigments responsible for detecting light have been shown to vary in their exact chemical composition due to genetic mutation; different individuals will have cones with different color sensitivity.Structure
Types
Humans normally have three types of cones, usually designated L, M and S for long, medium and short wavelengths respectively. The first responds the most to light of the longer red
While it has been discovered that there exists a mixed type of bipolar cells that bind to both rod and cone cells, bipolar cells still predominantly receive their input from cone cells.[9]
Other animals might have a different number of cone types (see Color vision).
Shape and arrangement
Cone cells are somewhat shorter than rods, but wider and tapered, and are much less numerous than rods in most parts of the retina, but greatly outnumber rods in the fovea. Structurally, cone cells have a cone-like shape at one end where a pigment filters incoming light, giving them their different response curves. They are typically 40–50 µm long, and their diameter varies from 0.5 to 4.0 µm, being smallest and most tightly packed at the center of the eye at the fovea. The S cone spacing is slightly larger than the others.[10]
Photobleaching can be used to determine cone arrangement. 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).[11]
Like rods, each cone cell has a synaptic terminal, inner and outer segments, as well as an interior nucleus and various
The outer segments of cones have invaginations of their
Function
The difference in the signals received from the three cone types allows the brain to perceive a continuous range of colors, through the
All of the receptors contain the protein
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 420 nm. However, the
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.[9]
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.
It is possible that S cones may play a role in the regulation of the circadian system and the secretion of melatonin but this role is not clear yet. The exact contribution of S cone activation to circadian regulation is unclear but any potential role would be secondary to the better established role of melanopsin (see also Intrinsically photosensitive retinal ganglion cell).[13]
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.[14]
Associated diseases
- Achromatopsia (Rod monochromacy) - a form of monochromacy with no functional cones
- Blue cone monochromacy- a rare form of monochromacy with only functional S-cones
- deuteranopia, etc.
- Oligocone trichromacy - poor visual acuity and impairment of cone function according to ERG, but without significant color vision loss.[15]
- Bradyopsia - photopic vision cannot respond quickly to stimuli.[15]
- Bornholm eye disease - X-linked recessive myopia, astigmatism, impaired visual acuity and red-green dichromacy.[15]
- Cone dystrophy - a degenerative loss of cone cells
- Retinoblastoma - a type of cancer originating from cone precursor cells
See also
- Disc shedding
- Double cones
- RG color space
- Tetrachromacy
- Melanopsin
- Color vision
List of distinct cell types in the adult human body
References
- ^ "The Rods and Cones of the Human Eye". HyperPhysics Concepts - Georgia State University.
- ^ ISBN 9780838577011.
- ^ Schacter, Gilbert, Wegner, "Psychology", New York: Worth Publishers,2009.
- ^
Jameson, K. A.; Highnote, S. M. & Wasserman, L. M. (2001). "Richer color experience in observers with multiple photopigment opsin genes" (PDF). Psychonomic Bulletin and Review. 8 (2): 244–261. S2CID 2389566.
- ^ "You won't believe your eyes: The mysteries of sight revealed". The Independent. 7 March 2007. Archived from the original on 6 July 2008. Retrieved 22 August 2009.
Equipped with four receptors instead of three, Mrs M - an English social worker, and the first known human "tetrachromat" - sees rare subtleties of colour.
- ^ Mark Roth (September 13, 2006). "Some women may see 100,000,000 colors, thanks to their genes". Pittsburgh Post-Gazette. Archived from the original on November 8, 2006. Retrieved August 22, 2009.
A tetrachromat is a woman who can see four distinct ranges of color, instead of the three that most of us live with.
- ISBN 978-0-471-02106-3.
- ISBN 978-0-470-02425-6.
- ^ PMID 20362067.
- ^ Brian A. Wandel (1995). Foundations of Vision. Archived from the original on 2016-03-05. Retrieved 2015-07-31.
- S2CID 4432043.
- ^ Let the light shine in: You don't have to come from another planet to see ultraviolet light The Guardian, David Hambling (May 30, 2002)
- ^ Soca, R (Feb 13, 2021). "S-cones and the circadian system". Keldik. Archived from the original on 2021-02-14.
- ^ Schacter, Daniel L. Psychology: the second edition. Chapter 4.9.
- ^ PMID 25770143.