Anatomy of
The visual system is a perfect anatomical organization, where each element behaves in a functional task that has to perform. The shape of the eye is close to that of the sphere, its diameter is about 2.7 cm. The eye, being composed of rigid materials, maintains its shape thanks to the fluid inside. Much of the outer covering of the eye is composed of a fibrous membrane called the sclera than in the front takes the shape of a transparent window called the cornea. The characteristic of the cornea is to be more convex the sclera. This part of the body, being devoid of blood vessels, can be considered independent of the eye. The maximum deviation of the light signals that the image is formed on the corneal surface. The fundamental task of this transparent membrane is to protect the eye from external agents. Wanting to make a comparison easy, we can say that the cornea is like the windshield of our Car that protects us from all that is external to the passenger compartment. Under the cornea lies the iris, with its wide range of eye pigment that gives intense color and detail to all of us known. The color of the iris, which can vary in the range of colors known to us, has no relevance to the vision, it only serves to shield the eyes from the rays coming from outside. Its function is to allow light to pass only through the pupil, which is nothing but the hole in the iris. Eyes dark in color and have increased protection for intense blue eyes. Pupil dilation, which can vary from 2 to 8 mm, is of particular importance for a correct view, because its aim is to pass the same amount of light signals. The image from the pupil ends up on the lens or crystalline, with its concave convex behavior, stimulated by the ciliary muscle has the task of accommodating the view, the lens is given the task of focus images. When the lens sits on near objects, the tension of the suspensory ligaments become loose allowing the lens to assume a convex shape. The same lens flattens when we focus on distant objects. Characteristic of the lens is to be made up of cells that renew themselves and then with the passage of time function of the lens stiffens the resulting lack of presbidia, typical in adults. While the lens is immediately behind the pupil and in contact with the iris, the greater distance between the lens and retina. This gap is filled by a gelatinous substance called vitreous humor. Signals accommodated by the lens, end up on the retina lining the concave side of the eye, which, through the optic nerve is in direct contact with the brain. The thin membrane that forms the retina, rich in blood vessels, is made up of nerve cells. Close to the optic nerve is the cavity which is a small foveal depression with the purpose of collecting the prevalence of the images in the form of electrochemical impulses are transmitted to the cervello.Fotorecettori retina.La retina consists of two groups of cells, called photoreceptors, which are called rods and cones. The cones, collected mainly near the fovea are those that allow us a photopic (color), while the rods allow us a vision of light and shade. Instead of the rods that are also active with very little light, the cones need a good light stimulation. All types of photoreceptors (rods and cones) in the presence of low light behave like rods. The discovery of the retinal function is relatively recent, considering the time between first theories of vision and the birth of modern optics. To find out the minute people receptor has had to await the discovery of the microscope. Only in 1835 Trevianus or the inclusion of a description similar to those recognized by modern science. Since the rods and cones sensitive cells attached to the optic nerve fibers, may be considered somewhat an expansion of the brain. That particular state of momentary blindness we experience when we move from a situation of strong light to one that has poor lighting, and depends on the sudden change in the role of rods and cones that must adapt quickly to a different condition. Normally, the transition from photopic to scotopic that occurs gradually and thus the light-sensitive cells have plenty of time to adapt to the lighting conditions present at the time. In such cases, the transition is sudden and abrupt, just before the cones that were responsible for color vision, assume the role of photoreceptors sensitive to just how many of luce.Visione cromatica.L 'aspect that differentiates these two groups of cells retina is of fundamental importance for what concerns color vision, which depends exclusively from the cones of the retina. It must be said first of all to see that the colors are not all species of animals. Color vision depends on the shape of the visual system which is different in the present case. The color vision requires two basic conditions: that there is a light source and that the cones in the retina are able to receive the stimulation of light. A high value for visual acuity and color perception is given by the fovea centralis. This small depression that could be called a kind of funnel where they end up images of color, has the important task of enabling the color vision of the world. When we look at an object to see it better we rotate the eye, allowing the image to fall within this cavity. The special activities just described is called a reflection of fixation. All the points on which we fix our gaze form the retinal images in the fovea, which is the only part of the eye where there are only cone cells fotorecettive. The explanation of the small number of these cells is that these are directly related to the nerve fibers, so you can work as individual connections with the brain. It can not be so for all the rods and cones, because their number is far higher than the optic nerve fibers. There are about 1,000,000 of optical fibers compared to 6,000,000 100,000,000 of rods and cones, but all the more delicate work is done by a few thousand cones in the fovea centralis. The field of view of the eye is the region of outer space, but the visual field of the eye motion is greater. When we rotate the eye to see, in fact broaden the field of view. Cells coniche.Le conical cells in turn are divided into three groups (three groups of ball boys imagine a football field), each of which is sensitive to certain wavelengths of light. A region is sensitive to wavelengths of red and orange, a significant power at wavelengths of green and yellow, the other in the blue and violet. Received the stimulus from the object that is as visible light, all three types of receptors capture the signal and send it to the brain according to the stimulation they received. The apparatus brain receives three different signals from the retina, which are then added resulting in the stimulation of the observed object. The colors in nature are not those spectral (rainbow), but the result of a more complex mix of electromagnetic waves. An orange that we would not hesitate to recognize in his traditional colors, reflected radiation between 510 and 680 nanometers. This means that the stimulus received by the eye activates the cones that can respond to these wavelengths. The brain always comes a hat-trick of electrochemical signals: if a group does not respond to certain wavelengths, the brain sends a stimulus equivalent to zero. We use color to television prove experimentally in a simple substance of these allegations. An experiment that can do all that it does not cost anything, is to spray a droplet of water on our television screen. That will show that the drop in us a magnifying glass, will be merged three diskettes and repeated endlessly, red, green and blue primary colors that, needless to say, correspond to regions of chromatic sensitivity of the cones of the retina . All the colors we see when we are watching a television program to be generated in primary secondary, tertiary and so on. These three little lights lit properly produce a color rather than another. If the blue disk is turned off while the green and red are on the same intensity as additive synthesis will get the yellow that is just the sum of green and red lights projected. E 'by the constant and continuous change in brightness of these disks on the screen that creates the sensation of color, which will make us seem like we're seeing the natural colors. On the other hand it is known that a minimum number of primary (three) can give rise to a wide range of colors possibili.Visone acromatica.Va have to remember that if a rattlesnake is able to see infrared, almost all mammals do not have a color vision. With man see the colors of insects, fish and birds: the visual acuity of the falcon is 7 times ours. Having a vision achromatic does not mean having to deal with limited vision. Each animal has a vision in keeping with requirements of survival. For a predator is more important to have a motion-sensitive device, optimally in low light conditions. If we, through peripheral vision on the rod, we can sense movement in the ear, which is a feline tiger or cat feel the movement from behind the head. In place of non-color vision, the presence of a wide gray scale, which offers a more flattering view of any animal.
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