Cones perceive the following colors. Functions of rods and cones in the retina

STICKS AND CONES

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

Scientific and technical encyclopedic dictionary.

See what "STICKS AND CONES" are in other dictionaries:

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AND; and. Anat. Inner photosensitive membrane of the eye; retina. * * * Retina (retina), the inner shell of the eye, consisting of many light-sensitive rod and cone cells (a person has about 7 million cones and 75 ... ... encyclopedic Dictionary

The organ of vision that perceives light. The human eye has spherical shape, its diameter is approx. 25 mm. The wall of this sphere ( eyeball) consists of three main shells: the outer, represented by the sclera and the cornea; middle, vascular tract,… … Collier Encyclopedia

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38. Photoreceptors (rods and cones), differences between them. Biophysical processes that occur when a light quantum is absorbed in photoreceptors. Visual pigments of rods and cones. Photoisomerization of rhodopsin. Mechanism of color vision.

.3. BIOPHYSICS OF LIGHT PERCEPTION IN THE RETINA The structure of the retina

The structure of the eye on which the image is obtained is called retina(mesh). In it, in the outermost layer, there are photoreceptor cells - rods and cones. The next layer is formed by bipolar neurons, and the third layer is formed by ganglion cells (Fig. 4). Between rods (cones) and bipolar dendrites, as well as between bipolar axons and ganglion cells, there are synapses. Axons of ganglion cells form optic nerve. Outside the retina (counting from the center of the eye) lies a black layer of the pigment epithelium, which absorbs the unused (not absorbed by the photoreceptors) radiation that has passed through the retina. On the other side of the retina (closer to the center) is choroid supplying oxygen and nutrients to the retina.

Rods and cones consist of two parts (segments) . Inner segment - this is an ordinary cell with a nucleus, mitochondria (there are a lot of them in photoreceptors) and other structures. Outer segment. almost entirely filled with discs, which are formed by phospholipid membranes (in rods up to 1000 discs, in cones about 300). The disc membranes contain approximately 50% phospholipids and 50% a special visual pigment, which in rods is called rhodopsin(for its pink color; rhodes is Greek for pink), and in cones iodopsin. For the sake of brevity, we will only talk about sticks in the following; the processes in cones are similar. The differences between cones and rods will be discussed in another section. Rhodopsin is made up of a protein opsin, to which is attached a group called retinal. . Retinal in its chemical structure is very close to vitamin A, from which it is synthesized in the body. Therefore, a lack of vitamin A can cause visual impairment.

Differences between rods and cones

1. difference in sensitivity. . The threshold for sensing light in rods is much lower than that of cones. This, firstly, is explained by the fact that there are more disks in rods than in cones and, therefore, there is a greater probability of absorption of light quanta. However, main reason in a different. Neighboring rods using electrical synapses. combined into complexes called receptive fields .. electrical synapses (connexons) can open and close; therefore, the number of rods in the receptive field can vary widely depending on the amount of illumination: the weaker the light, the larger the receptive fields. In very low light, over a thousand sticks can combine in a field. The meaning of such a combination is that it increases the ratio of useful signal to noise. As a result of thermal fluctuations on the membranes of the rods, a randomly changing potential difference arises, which is called noise. In low light, the amplitude of the noise can exceed the useful signal, that is, the amount of hyperpolarization caused by the action of light. It may seem that under such conditions the reception of light will become impossible. However, in the case of perception of light not by a separate stick, but by a large receptive field, there is a fundamental difference between noise and a useful signal. The useful signal in this case arises as the sum of the signals generated by the sticks combined into a single system - receptive field . These signals are coherent, they come from all rods in the same phase. Noise signals due to the chaotic nature of thermal motion are incoherent, they come in random phases. It is known from the theory of addition of oscillations that for coherent signals the total amplitude is equal to : Asum = A 1 n, Where A 1 - single signal amplitude, n- number of signals. In the case of incoherent. signals (noise) Asumm=A 1 5.7n. Let, for example, the amplitude of the useful signal be 10 μV, and the amplitude of the noise be 50 μV. It is clear that the signal will be lost against the background of noise. If 1000 rods are combined into a receptive field, the total useful signal will be 10 μV

10 mV, and the total noise is 50 μV 5. 7 \u003d 1650 μV \u003d 1.65 mV, that is, the signal will be 6 times more noise. With this attitude, the signal will be confidently received and will create a feeling of light. Cones work in good light, when even in a single cone the signal (PRP) is much more than noise. Therefore, each cone usually sends its own signal to the bipolar and ganglion cells independently of the others. However, if the light is reduced, the cones can also combine into receptive fields. True, the number of cones in the field is usually small (several tens). In general, cones provide daytime vision, rods provide twilight vision.

2.Resolution difference.. The resolving power of the eye is characterized by the minimum angle at which two adjacent points of the object are still visible separately. Resolution is mainly determined by the distance between adjacent photoreceptor cells. In order for two points not to merge into one, their image must fall on two cones, between which there will be another one (see Fig. 5). On average, this corresponds to a minimum visual angle of about one minute, that is, the resolution of cone vision is high. Rods are usually combined into receptive fields. All points whose images fall on one receptive field will be perceived

swear as one point, since the entire receptive field sends a single total signal to the central nervous system. That's why resolving power (visual acuity) with rod (twilight) vision is low. With insufficient illumination, the rods also begin to combine into receptive fields, and visual acuity decreases. Therefore, when determining visual acuity, the table must be well lit, otherwise a significant mistake can be made.

3. The difference in placement. When we want to get a better view of an object, we turn so that this object is in the center of the field of view. Since cones provide high resolution, it is cones that predominate in the center of the retina - this contributes to good visual acuity. Since the color of the cones is yellow, this area of the retina is called the macula lutea. On the periphery, on the contrary, there are much more rods (although there are also cones). There visual acuity is noticeably worse than in the center of the field of view. In general, there are 25 times more rods than cones.

4. Difference in color vision.Color vision is unique to cones; the image given by the chopsticks is one-color.

Color vision mechanism

In order for a visual sensation to arise, it is necessary that light quanta be absorbed in photoreceptor cells, or rather, in rhodopsin and iodopsin. The absorption of light depends on the wavelength of the light; each substance has a specific absorption spectrum. Studies have shown that there are three types of iodopsin with different absorption spectra. At

of one type, the absorption maximum lies in the blue part of the spectrum, the other - in green and the third - in red (Fig. 5). There is one pigment in each cone, and the signal sent by this cone corresponds to the absorption of light by this pigment. Cones containing a different pigment will send different signals. Depending on the spectrum of light incident on a given area of the retina, the ratio of signals coming from different types of cones turns out to be different, and in general, the totality of signals received by the visual center of the CNS will characterize the spectral composition of the perceived light, which gives subjective sense of color.

Information about the world around 90% of a person receives through the organ of vision. The role of the retina is a visual function. The retina consists of photoreceptors of a special structure - cones and rods.

Rods and cones are photographic receptors with a high degree of sensitivity; they convert light signals coming from outside into impulses perceived by the central nervous system - the brain.

When illuminated - during daylight hours – increased load cones are tested. The rods are responsible for twilight vision - if they are not active enough, night blindness.

The cones and rods in the retina of the eye have different structure because their functions are different.

The structure of the human eye

The organ of vision also includes vascular part and the optic nerve, which transmits signals received from the outside to the brain. The part of the brain that receives and converts information is also considered one of the parts of the visual system.

Where are the rods and cones located? Why are they not listed? These are receptors nervous tissue that make up the retina. Thanks to cones and rods, the retina receives an image fixed by the cornea and the lens. The impulses transmit the image to the central nervous system, where the information is processed. This process is carried out in a matter of fractions of a second - almost instantly.

Most of the sensitive photoreceptors are located in the macula - this is the name of the central region of the retina. The second name of the macula is yellow spot eyes. This name was given to the macula because when examining this area, a yellowish tint is clearly visible.

The structure of the outer part of the retina includes pigment, the inner part contains light-sensitive elements.

Cones in the eye

Cones got their name because they are similar in shape to flasks, only very small. In an adult, the retina includes 7 million of these receptors.

Each cone consists of 4 layers:

outer - membrane discs with a color pigment iodopsin; it is this pigment that provides high sensitivity when perceiving light waves of various lengths;
connecting tier - the second layer - constriction, which allows to form the shape of a sensitive receptor - consists of mitochondria;
the inner part - the basal segment, the link;
synaptic area.

Currently, only 2 light-sensitive pigments in the composition of photoreceptors of this type, chlorolab and erythrolab, have been fully studied. The first is responsible for the perception of the yellow-green spectral region, the second - the yellow-red.

Sticks in the eyes

The rods of the retina are cylindrical in shape, the length exceeds the diameter by 30 times.

The composition of the sticks includes the following elements:

membrane discs;
cilia;
mitochondria;
nervous tissue.

Maximum light sensitivity is provided by the pigment rhodopsin (visual purple). He cannot distinguish between color shades, but he reacts even to minimal light flashes that he receives from the outside. The rod receptor is excited even by a flash, the energy of which is only one photon. It is this ability that allows you to see at dusk.

Rhodopsin is a protein from the group of visual pigments, belongs to chromoproteins. It received its second name - visual purple - during research. Compared to other pigments, it stands out sharply with a bright red tint.

Rhodopsin contains two components - a colorless protein and a yellow pigment.

The reaction of rhodopsin to a light beam is as follows: when exposed to light, the pigment decomposes, causing excitation optic nerve. IN daytime the sensitivity of the eye shifts to the blue region, to the night - visual purple is restored within 30 minutes.

During this time, the human eye adapts to twilight and begins to more clearly perceive the surrounding information. It is this that can explain that in the dark, over time, they begin to see more clearly. The less light enters, the more acute twilight vision.

Cones and rods of the eye - functions

It is impossible to consider photoreceptors separately - in visual apparatus they form a whole and are responsible for visual functions and color perception. Without the coordinated work of both types of receptors, the central nervous system receives garbled information.

Color vision is provided by the symbiosis of rods and cones. Rods are sensitive in the green part of the spectrum - 498 nm, no more, and then cones with different types pigment.

To assess the yellow-red and blue-green range, long-wave and medium-wave cones with wide light-sensitive zones and internal overlap of these zones are involved. That is, photoreceptors react simultaneously to all colors, but they are excited more intensively to their own.

At night, it is impossible to distinguish colors, one color pigment can only respond to light flashes.

Diffuse biopolar cells in the retina form synapses (the point of contact between a neuron and a cell receiving a signal, or between two neurons) with several rods at once - this is called synaptic convergence.

Increased perception of light radiation is provided by monosynaptic bipolar cells that connect cones with a ganglion cell. A ganglion cell is a neuron that is located in the retina of the eye and generates nerve impulses.

Together, rods and cones bind amacrylic and horizontal cells, so that the first processing of information occurs even in the retina itself. This provides a quick reaction of a person to what is happening around him. Amacrylic and horizontal cells are responsible for lateral inhibition - that is, the excitation of one neuron produces "soothing" action on another, which increases the sharpness of perception of information.

Despite the different structure of photoreceptors, they complement each other's functions. Thanks to their coordinated work, it is possible to obtain a sharp and clear image.

The cones of the retina of the eyeball are one of the varieties of photoreceptors, which is part of the layer responsible for photosensitivity. Cones are one of the most complex and important structures of the structure. human eye responsible for the ability to distinguish color scheme. By changing the received light energy into electrical impulses, they send information about the world that surrounds a person to certain parts of the brain. Neurons process the received signal and recognize a large number of colors and their shades, but not all of these processes have been studied today.

The cones got their name because they appearance very similar to an ordinary laboratory flask.

Rods and cones are sensitive receptors in the retina of the eye that transform light stimuli into nervous

The cone is 0.05 mm long and 0.004 wide. The diameter of the narrowest point of the cone is 0.001 mm. Despite the fact that their size is very small, the accumulation of cones on the retina is in the millions. This photoreceptor, despite its microscopic size, has one of the most complex anatomy and consists of several departments:

In the outdoor department there is an accumulation of plasmalemes, from which semi-disks are formed. The number of such accumulations in the organs of vision is estimated in the hundreds. Also in the outer section contains the pigment iodopsin, which is involved in the mechanisms of color vision.
Binding Department- the tightest part of the cone. The cytoplasm located in the department has the structure of a very thin rope. In the same section, there are two eyelashes with an unusual structure.
In internal department cells responsible for the functioning of the receptor are located. Also here are the nucleus, mitochondria and ribosome. Such a neighborhood may indicate that in the internal section, intensive processes of energy production are taking place, which are necessary for the proper functioning of photoreceptors.
Synaptic department, serves as a link between receptors that are sensitive to light and nerve cells. It is in this section that contains a substance that plays a major role in the transmission of impulses from the layer of the retina responsible for light perception to the optic nerve.

How photoreceptors work

The process by which cones work is still not understood. Today there are two leading versions that can most accurately describe this process.

Cones are responsible for visual acuity and color perception (day vision)

Three-component vision hypothesis

Adherents of this version say that in the retina of the human eye, there are several types of cones containing different pigments. Iodopsin - the main pigment located in the outer part of the cones, has 3 varieties:

erythrolab;
chlorolab;
cyanolab;

And if the first two varieties of the pigment have already been studied in detail, then the existence of the third takes place only in theory, and its existence is confirmed only by indirect facts. So what color are the retinal cones sensitive to? If we use this theory as the main one, we can say the following. Cones, which contain erythrolab, are capable of perceiving only radiation that has long waves, and this is the yellow-red part of the spectrum. Radiation having an average length or a yellow-green part of the spectrum is perceived by cones containing chlorolab.

The assertion that there are cones that process short-wave radiation (shades of blue color), and it is on this statement that the three-component structure theory is built eye retina.

Nonlinear two-component theory

Proponents of this theory completely deny the existence of a third type of pigment. They are justified by the fact that for normal light perception of the remaining parts of the spectrum, it is sufficient to have the operation of such a mechanism as sticks. Based on this, it can be argued that retina eyeball is able to perceive the entire color gamut only when joint work cones and rods. This theory also implies that the interaction of these structures gives rise to the ability to determine the presence of yellow shades in the gamut. visible colors. To what color the cones of the retina are selectively sensitive, there is no answer today, since this issue is not resolved.

There are about 7 million cones on the retina of a healthy adult.

The existence of people with a rare anomaly - an additional cone of the eye retina has been scientifically proven. This means that in people with this phenomenon, another photoreceptor is located in the eyeball. People with this anomaly are able to distinguish 10 times more shades than a person with normal amount receptors. Conflicting studies provide the following data.

Identified pathology occurs only in 2% of the population, and exclusively female. However, the second research group claims that today such a feature is found in a quarter of the Earth's population.

Retina - the retina of the eyeball, is able to perceive information fully, only when correct work all internal mechanisms. If one of the components does not produce necessary substances, then the perception of the color spectrum is significantly narrowed. This phenomenon has received common name colorblindness. Patients with this diagnosis do not have the ability to distinguish certain colors, since the disease is genetic heredity and does not have a specific method of treatment.

The sticks have the shape of a cylinder with an uneven, but approximately equal diameter of the circle along the length. In addition, the length (equal to 0.000006 m or 0.06 mm) is 30 times their diameter (0.000002 m or 0.002 mm), which is why the elongated cylinder is really very similar to a stick. in the eye healthy person there are about 115-120 million sticks.

The wand of the human eye consists of 4 segments:

1 - Outer segment (contains membrane discs),

2 - Connecting segment (eyelash),

4 - Basal segment (nerve connection)

The sticks are extremely light sensitive. Enough energy of one photon (the smallest, elementary particle of light) for the reaction of sticks. This fact helps with so-called night vision, allowing you to see at dusk.

The rods are not able to distinguish colors, first of all, this is due to the presence of only one rhodopsin pigment in the rods. Rhodopsin, or otherwise it is called visual purple, due to the inclusion of two groups of proteins (chromophore and opsin) has two light absorption maxima, although, given that one of these maxima is beyond the light visible to the human eye (278 nm is the ultraviolet region, not visible to the eye), it is worth calling them wave absorption maxima. However, the second absorption maximum is still visible to the eye - it is located at around 498 nm, which is, as it were, on the border between green color spectrum and blue.

It is reliably known that the rhodopsin contained in the rods reacts to light more slowly than the iodopsin in the cones. Therefore, the sticks are less responsive to the dynamics of the light flux and poorly distinguish objects in motion. For the same reason, visual acuity is also not a specialization of the rods.

Cones of the retina

Cones got their name because of their shape, similar to laboratory flasks. The length of the cone is 0.00005 meters, or 0.05 mm. Its diameter at its narrowest point is about 0.000001 meters, or 0.001 mm, and 0.004 mm at its widest. There are about 7 million cones in a healthy adult.

Cones are less sensitive to light, in other words, to excite them, a light flux is required ten times more intense than to excite rods. However, cones are able to process light more intensely than rods, which is why they perceive changes in the light flux better (for example, rods are better at distinguishing light in dynamics when objects move relative to the eye), and also determine a clearer image.

The cone of the human eye consists of 4 segments:

1 - Outer segment (contains membrane disks with iodopsin),

2 - Connecting segment (constriction),

3 - Inner segment (contains mitochondria),

4 - Area of synaptic connection (basal segment).

The reason for the above properties of cones is the content of the biological pigment iodopsin in them. At the time of writing this article, two types of iodopsin were found (isolated and proven): erythrolab (pigment sensitive to the red part of the spectrum, to long L-waves), chlorolab (pigment sensitive to the green part of the spectrum, to medium M-waves). To date, a pigment that is sensitive to the blue part of the spectrum, to short S-waves, has not been found, although the name cyanolab has already been assigned to it.

The division of cones into 3 types (according to the dominance of color pigments in them: erythrolab, chlorolab, cyanolab) is called the three-component hypothesis of vision. However, there is also a non-linear two-component theory of vision, whose adherents believe that each cone simultaneously contains both erythrolab and chlorolab, which means that it is able to perceive the colors of the red and green spectrum. At the same time, the faded rhodopsin from the rods takes on the role of cyanolalab. In support of this theory, it is also said that people suffering, namely in the blue part of the spectrum (tritanopia), also have difficulty with twilight vision(night blindness), which is a sign of abnormal work of the rods of the retina.