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What is a Cone Cell?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 27 November 2016
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A cone cell or simply “cone” is a specialized light-sensitive cell found in the retina of the eye and used for discrimination of color and detail. In humans, three cone cell types are present, sensitized to different ranges of wavelength to provide a range of color perception. Different organisms have varying numbers of cones, sensitized to different areas of the spectrum, allowing animals like bees to perceive infrared light while humans cannot.

As the name suggests, part of the shape of a cone cell is indeed like that of a cone. The cone-shaped segment sits on top of the cell and reacts to different wavelengths of light, depending on the concentration of photopigment present in the structure. As this structure reacts, it sends a signal to the main body of the cone cell, and the input from scores of cone cells is used to create a complete picture for the brain. There are over four million cone cells in the eye, and they are especially densely packed in the fovea, a key area of the eye.

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These cells are less sensitive to light than their fellow rod cells. Rod cells function in very low light, but do not respond to color, and have a rod-like structure. Organisms have varying concentrations of rod and cone cells depending on the environments where they evolved. Animals in need of good vision in low-light settings, like nocturnal animals, have many more rods, as these cells are more useful. Animals used to bright light and in need of color differentiation, like humans, tend to have an increased number of cone cells, although rods still outnumber cones.

Cones are sensitive to yellowish-green, blue-violet, and green light. When people perceive scenes in color, they do so with assistance from millions of these cells, each providing a small piece of the puzzle. When the cells sensitive to green light fire most strongly, for example, it is an indicator that the person is looking at something green, like a tree. Varying intensities of light provided by rods create shading and selective firing of yellow-green cones may reveal new growth, typically a lighter green.

People with disorders of color vision may have a cone cell problem, although there are other causes of colorblindness. Some people have no cones at all and cannot perceive color, while others have decreased numbers or defective cones, experiencing impaired color vision. When people are diagnosed with colorblindness, tests can be performed to learn more about why they have difficulties with color vision.

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JimmyT
Post 4

@TreeMan - You are on the right track, but colorblindness is actually found on the X chromosomes. Females are much less likely to be colorblind, but the fact that they can be means it can't be on the Y chromosome. The reason that females are less likely is because males only have one X chromosome, so a bad gene on that one chromosome means they will be colorblind, but a female has a second X that can make up for the first X chromosome having the colorblind gene. In other words, to be colorblind, a female would have to have two colorblind genes, whereas a male just has to have one.

Something I have been wondering about is kind of

the reverse of colorblindness. I am curious if it is possible for some people to have extra sensitive cone cells or else just extra cone cells in general. Are there some people who are able to see colors more vividly than the normal person or see outside the normal range of colors? I have never heard of it, but it seems like it could be possible.
TreeMan
Post 3

Wow, I knew about people being colorblind, of course, but I had no idea that some people weren't able to see color at all. Is that some sort of a rare genetic disorder, or what causes that? Even with colorblindness, what is the cause? I would assume it is genetic, but how? I have heard that males are more likely to have trouble seeing colors than females, so is it somthing to do with the Y chromosome?

Is there any way that a person can become colorblind just through natural causes? I mean like, can a person be born seeing fine and then lose their color vision sometime later in life?

Izzy78
Post 2

@matthewc23 - Good question. As for dogs, though, they actually can see in color. It is just a common thing that a lot of people say dogs can't see in color. Scientists have found cones and rods in dog eyes. Like the article talks about, though, dogs just have a lot more rods than they do cones, and I don't think they have all of the same types as humans do.

I know the example I alway hear and have seen with my dogs is that if you have a green ball and throw it in the grass at a distance, it will be harder for the dogs to find it, since they have a harder time picking out different

shades of green.

As far as humans go with colorblindness, I'm not sure. I want to say that at some point I heard something about colorblind people actually having cones that weren't shaped correctly. I'm not sure how accurate that is, though.

matthewc23
Post 1

I always wondered what the difference was between rods and cones. I always hear the words used, but never really knew the difference.

Since dogs can't see in color, I guess that would mean they don't have cones, right? Wouldn't they have more rods, though, since they can see better in the dark?

I am not colorblind, but I know a couple of people who are. I know one of the biggest problems is that people can't tell the difference between red and green. Does that mean they they just have many more red color cone cells than green or are the green ones somehow defective, and it makes them seed green as red? I have never really understood how it works. Does anyone know?

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