Thanks to vision, a person perceives the surrounding reality and orients himself in space. Of course, without the other senses it is difficult to form a complete picture of the world, but the eyes perceive almost 90% of general information, which enters the brain from the outside.

By using visual function a person is able to see phenomena occurring near him, can analyze various events, find differences between one object and another, and also notice an impending threat.

The organs of vision are designed in such a way that they distinguish not only the objects themselves, but also the color diversity of living and inanimate nature. The responsibility for this lies with special microscopic cells - rods and cones present in the retina of the eye. They are the ones the initial link in the chain of transmitting information about the object seen to occipital part brain.

IN structural structure The retina has a very specific area allocated to the cones and rods. These visual receptors, penetrating the nervous tissue that forms the retina of the eye, contribute to the rapid conversion of the resulting light flux into a combination of impulses.

An image is formed in the retina, designed with the direct participation of the eye area of ​​the cornea and lens. At the next stage, the image is processed, after which nerve impulses, moving along the visual pathway, deliver information to the desired part of the brain. The complex and fully formed structure of the eyes makes it possible to instantly process any information.

The main share of photographic receptors is concentrated in the so-called macula. This is the area of ​​the retina located in its central zone. Because of its corresponding color, the macula is also called the yellow spot of the eye.

Cones are the visual receptors that respond to light waves. Their functioning is directly related to a special pigment - iodospin. This multi-component pigment consists of chlorolab (responsible for the perception of the green-yellow spectrum) and erythrolab (sensitive to the red-yellow spectrum). Today these are two thoroughly studied pigments.

In a person with perfect vision There are almost seven million cones in the retina. They are microscopic in size and inferior in geometric parameters to rods. The length of a single cone is about fifty micrometers, and the diameter is about four. It should be noted that the sensitivity of cones to light rays is approximately one hundred times lower than that of rods. However, thanks to them, the eye can qualitatively perceive sudden movements of objects.

The cones form four distinct zones. The outer region is represented by half-discs. The banner acts as a connecting section. The inner region contains a set of mitochondria. Finally, the fourth zone is the area of ​​neural contacts.

1. The outer region is entirely formed by half-discs formed from the plasma membrane. These are membrane folds of microscopic size, completely covered with sensitive pigments. Regular phagocytosis of these formations, as well as their constant renewal in the receptor body, allows the outer region of the cone to be renewed. Pigment production occurs in this area. Up to one hundred half-disc plasma membranes can be renewed in a day. It will take approximately two weeks to fully restore the entire set of half-discs.
2. The connecting region, protruding the membrane, creates a bridge between the outer and inner sections of the cones. Communication is established with the participation of a pair of cilia and the internal contents of cells. Cilia and cytoplasm can move from one area to another.
3. The inner region is a zone of active metabolism. The mitochondria that fill this zone transport the energy substrate for visual function. This part contains the core.
4. Synaptic area. This is where the energetic contact of bipolar cells occurs.

Visual acuity is influenced by monosynaptic bipolar cells connecting cones and ganglion cells.

There are three types of cones depending on their sensitivity to spectral waves:

• S-type. They demonstrate sensitivity to short wavelengths of blue-violet light.
• M-type. Cones that detect from the mid-wave spectrum. This is a yellow-green color scheme.
• L-type. Sensitive to long wavelengths of red-yellow color.

The shape of the sticks is similar to a cylinder, having a uniform diameter along the entire length. The length of these eye receptors is almost thirty times greater than their diameter, so the shape of the rods is visually elongated. The retinal rods consist of four elements: membrane discs, cilia, mitochondria and nerve tissue.

The sticks have maximum light sensitivity, which guarantees their response to the slightest flash of light. The rod receptor apparatus will be activated even when exposed to one photon of energy. This unique ability of the rods helps a person navigate in the twilight and ensures maximum clarity of objects in dark time days.

Unfortunately, rods contain only one pigment element, called rhodopsin. It is also referred to as visual purple. The fact that the pigment is only in a single copy does not allow these visual receptors to distinguish shades and colors. Rhodopsin does not have the ability to instantly respond to an external light stimulus, as cone pigments can do.

Being a complex protein compound containing a set visual pigments, rhodopsin belongs to the group of chromoproteins. It owes its name to its bright red color. The purple hue of the retinal rods has been discovered as a result of numerous laboratory research. Visual purple has two components - a yellow pigment and a colorless protein.

Under the influence of light rays, rhodopsin begins to rapidly decompose. Its breakdown products influence the formation of visual excitability. Once restored, rhodopsin supports twilight vision. In bright light, the protein decomposes, and its light sensitivity shifts to the blue area of ​​vision. Full recovery squirrel sticks healthy person may take approximately half an hour. During this period of time, night vision reaches its maximum level, and the person begins to view the outlines of objects.

Symptoms of damage to the rods and cones of the eyes

Pathologies marked by damage to these visual receptors are accompanied by the following symptoms:

• Visual acuity is lost.
• Sudden flashes and glare appear before the eyes.
• The ability to see in the dark decreases.
• A person cannot tell the difference between different colors.
• The fields are narrowing visual perception. IN in rare cases tubular vision is formed.

Diseases that are associated with impaired photoreceptor functions of rods and cones:

• Colorblindness m. Hereditary congenital pathology, expressed in the inability to distinguish colors.
• Hemeralopia. The pathology of the rods causes a decrease in visual acuity in the dark.
• Retinal detachment eyes.
• Macular degeneration. Impaired nutrition of the blood vessels of the eye leads to a decrease in central vision.

There are two types of photoreceptors: rods, which are sensitive to low level lighting, and cones, which are sensitive to light various areas spectrum

The vast majority of photoreceptors in the eye are rods. It is estimated that the retina contains approximately 120 million rods and only 6 million cones. In addition, rods are approximately 300 times more sensitive to light than cones.

Night vision

Their abundance and high light sensitivity make the rods an ideal tool for seeing at dusk and in low light levels. However, rods transmit to the brain only black and white image low definition. This is because “the number of rods, especially in the periphery of the retina, greatly exceeds the number of bipolar cells, which, in turn, transmit electrical impulses to the brain through an even smaller number of ganglion neurons.

Thus, it turns out that one ganglion cell transmitting information from the eye through optic nerve, gives the brain information collected from a large number of rods. That is why the visible image at twilight appears to be composed of a large number of large gray spots.

Electron micrograph of a group of rods (shown in green). The sticks are very sensitive to light and are therefore used mainly at dusk.

Day vision

Unlike rods, cones function primarily in strong light and allow the brain to construct a high-quality color image. This is facilitated by the fact that each individual cone has a “straight line” connecting it to the brain: one cone is connected to one bipolar cell, which, in turn, interacts with only one ganglion neuron. Thus, the brain receives information about the activity of each individual cone.

With the help of vision, a person gets acquainted with the world around him and orients himself in space. Undoubtedly, other organs are also important for normal life, but it is through the eyes that people receive 90% of all information. The human eye is unique in its structure; it is capable of not only recognizing objects, but also distinguishing shades. The rods and cones of the retina are responsible for color perception. They are the ones who transmit information obtained from environment, into the brain.

The eyes take up very little space, but at the same time they contain a huge number of different anatomical structures with the help of which a person sees.

The visual apparatus is almost directly connected to the brain, during special ophthalmological examinations the intersection of the optic nerve can be seen.

The eye includes elements such as vitreous, lens, anterior and posterior chambers. The eyeball visually resembles a ball and is located in a recess called the orbit, which forms the bones of the skull. On the outside, the visual apparatus is protected in the form of sclera.

Eye shells

The sclera occupies approximately 5/6 of the entire surface of the eye; its main purpose is to prevent injury to the organ of vision. Part of the inner shell comes out and is constantly in contact with negative external factors, it is called the cornea. This item has a number of characteristics thanks to which a person clearly distinguishes objects. These include:

• Light transmittance and refractive ability;
• Transparency;
• Smooth surface;
• Humidity;
• Specularity.

The hidden part of the inner shell is called the sclera, it consists of dense connective tissue. Below it is located vascular system. Middle section includes the iris, ciliary body and choroid. It also includes the pupil, which is a microscopic hole into which the iris does not extend. Each of the elements has its own functions necessary to ensure the smooth operation of the organ of vision.

The structure of the retina

The inner shell of the visual apparatus is an important part of the brain matter. It consists of numerous neurons that cover the inside of the entire eye. It is thanks to the retina that a person distinguishes objects around him. Refracted light rays are concentrated on it and a clear image is formed.

The nerve endings of the retina pass along the visual fibers, from where information is transmitted to the brain along the fibers. Also located here small speck yellow called the macula. It is located in the center of the retina and has the greatest capacity for visual perception. The macula is home to the rods and cones, which are responsible for day and night vision.

Cones and rods - functions

Their main purpose is to give a person the opportunity to see. The elements act as unique converters of black-and-white and color vision. Both types of cells belong to the category of light-sensitive receptors.

The cones of the eye get their name from their shape, which visually resembles a cone. They connect the central nervous system and the retina. The main function is to convert light signals from external environment into electrical impulses processed by the brain. The rods of the eye are responsible for night vision; they also contain a pigment element - rhodopsin; when rays of light hit it, it becomes discolored.

Cones

Photoreceptor by appearance resembles a cone. The retina contains up to seven million cones. However, large number does not mean gigantic parameters. The element has a modest length (only 50 microns), the width is four millimeters. Contains the pigment iodopsin. Less sensitive than sticks, but quicker to respond to movements.

Cone structure

The receptor contains:

• External element (membrane discs);
• Intermediate part (constriction);
• Internal section (mitochondria);
• Synaptic area.

Three-component hypothesis of color perception

There are three types of cones, each containing a unique variety of iodopsin and perceiving a specific part of the color spectrum:

• Chlorolab (M-type). Reacts to yellow and green shades;
• Erythrolab (L-type). Perceives yellow-red colors;
• Cyanolab (S-type). Responsible for the reaction to the blue and violet part of the spectrum.

Modern scientists studying the three-component system of visual perception note its imperfection, since the existence of three types of cones has not been scientifically proven. In addition, to date the cyanolab pigment has not been discovered.

Two-component hypothesis of color perception

This hypothesis states that the cones contain only eritolab and chlorolab, which perceive the long and middle parts of the color spectrum, respectively. Rhodopsin, which is the main component of rods, is responsible for short waves.

This statement is supported by the fact that patients who cannot distinguish the blue spectrum (i.e. short waves) suffer from problems with night vision.

Sticks

This receptor starts working when there is not enough light outside or indoors. In appearance they resemble a cylinder. There are approximately one hundred and twenty million rods concentrated in the retina. This large element has modest parameters. It is characterized by its small length (about 0.06 mm) and width (about 0.002 mm).

Structure

The sticks consist of four main elements:

• External department. Presented in the form of membrane disks;
• Intermediate area (eyelash);
• Internal sector (mitochondria);
• Tissue base with nerve endings.

The receptor reacts to the weakest flashes of light because it has a high degree of sensitivity. The sticks contain unique substance called visual purple. In good lighting conditions, it disintegrates and sensitively perceives the blue visual spectrum. At night or in the evening, the substance is regenerated, and the eye distinguishes objects even in pitch darkness.

Rhodopsin received an unusual name due to its blood-red hue, which turns yellow in the light and then becomes completely discolored.

Features of the transmission of light pulses

Rods and cones perceive the flow of light and direct it to the central nervous system. Both cells are able to work fruitfully in daytime days. The main difference is that cones are more sensitive to light than rods.

Interneurons are responsible for signal transmission; several receptors are simultaneously attached to each cell. By connecting a series of rods, the degree of sensitivity of the visual apparatus increases. In ophthalmology, the phenomenon is called “convergence”. Thanks to it, a person can simultaneously examine several visual fields at once and catch the slightest fluctuations in light fluxes.

Ability to perceive colors

Both photoreceptors are required by the eyes to distinguish between day and night vision and detect color images. The unique structure of the eye gives a person a huge number of opportunities: to see at any time of the day, to perceive a large area of ​​the surrounding world, etc.

Also, human eyes have an unusual ability - binocular vision, significantly expanding the overview. Rods and cones take part in the perception of the entire color spectrum, therefore, unlike animals, people distinguish all shades of the surrounding world.

Symptoms of damage to rods and cones

When a disease develops in the body that affects the main receptors of the retina, the following signs are observed:

• Decrease in visual acuity;
• Colorblindness;
• The appearance of bright glare before the eyes;
• Problems with night vision;
• Narrowing of visual field.

Some pathologies have specific symptoms, so it won’t be difficult to diagnose them. These include color blindness and " night blindness" To identify other diseases, you will need to undergo additional medical examination.

Diagnostic methods for damage to rods and cones

If you suspect the development pathological processes in the visual apparatus, the patient is sent for the following studies:

• Ophthalmoscopy. Used to analyze the condition of the fundus;
• Perimetry. Studies visual fields;
• Computer refractometry. Used to identify diseases such as myopia, hypermetropia or astigmatism;
• Ultrasound examination;
• Diagnostics of color perception. To do this, ophthalmologists most often use the Ishihara test;
• Fluorescence hagiography. Helps visually assess the condition of the vascular system.

The sticks have maximum light sensitivity, which ensures their response to even the most minimal external light flashes. The rod receptor begins to operate even when receiving energy of one photon. This feature allows the rods to provide twilight vision and helps to see objects as clearly as possible in the evening hours.

However, since the retinal rods contain only one pigment element, designated rhodopsin or visual purple, shades and colors cannot differ. The rod protein rhodopsin cannot react as quickly to light stimuli as the pigment elements of cones do.

Cones

The coordinated work of rods and cones, despite the fact that their structure differs significantly, helps a person to see the entire surrounding reality in full qualitative volume. Both types of retinal photoreceptors complement each other in their work, this helps to obtain the most clear, clear and bright image possible.

Cones get their name because their shape is similar to the flasks used in various laboratories. The adult retina contains about 7 million cones.
One cone, like a rod, consists of four elements.

• The outer (first) layer of the cones of the retina is represented by membrane discs. These discs are filled with iodopsin, a color pigment.
• The second layer of cones in the retina is the connecting tier. It acts as a constriction, which allows the formation of a certain shape of this receptor.
• The inner part of the cones is represented by mitochondria.
• In the center of the receptor there is a basal segment that acts as a connecting link.

Iodopsin is divided into several types, which allows for full sensitivity of cones visual pathway in perception various parts light spectrum.

By dominance different types pigment elements, all cones can be divided into three types. All these types of cones work in concert, and this allows a person to normal vision appreciate all the richness of shades of the objects he sees.

Structure of the retina

IN general structure The rods and cones occupy a very specific place in the retina. The presence of these receptors on the nervous tissue that makes up the retina helps quickly convert the received light flux into a set of impulses.

The retina receives the image, which is projected by the eye area of ​​the cornea and the lens. After this, the processed image in the form of impulses arrives through the visual pathway to the corresponding part of the brain. The complex and fully formed structure of the eye allows complete processing of information in a matter of moments.

Most of the photoreceptors are concentrated in the macula - the central region of the retina, which, due to its yellowish tint, is also called macular spot eyes.

Functions of rods and cones

The special structure of the rods allows them to detect the slightest light stimuli at the lowest degree of illumination, but at the same time these receptors cannot distinguish the shades of the light spectrum. Cones, on the contrary, help us see and appreciate all the richness of the colors of the world around us.

Despite the fact that, in fact, rods and cones have different functions, ensure uninterrupted operation the whole eye can only be coordinated by the participation of both groups of receptors.

Thus, both photoreceptors are important for our visual function. This allows us to always see a reliable picture, regardless of weather conditions and time of day.

Rhodopsin - structure and functions

Rhodopsin is a group of visual pigments, the structure of a protein belonging to chromoproteins. Rhodopsin, or visual purple, gets its name from its bright red hue. The purple coloration of the retinal rods has been discovered and proven in numerous studies. The retinal protein rhodopsin consists of two components - a yellow pigment and a colorless protein.

Under the influence of light, rhodopsin decomposes, and one of the products of its decomposition affects the occurrence of visual stimulation. Reduced rhodopsin acts in twilight lighting, and the protein is responsible for night vision at this time. In bright light, rhodopsin decomposes and its sensitivity shifts to the blue region of vision. The retinal protein rhodopsin is completely restored in humans in about 30 minutes. During this time, twilight vision reaches its maximum, that is, a person begins to see more clearly in the dark.

ROD AND CONES

ROD AND CONES(photoreceptors), cells of the RETINA, sensitive to light. The rods are located in the colored layer, secrete RHODOPSIN and are RECEPTORS for low intensity light. Cones secrete iodope-syn and are adapted to distinguish colors. The rods distinguish only shades of black and white, but are especially sensitive to movement.

Scientific and technical encyclopedic dictionary.

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