Sticks provide. Functions of rods and cones in the retina

Cones and rods are sensitive photoreceptors located in the retina. They convert light stimulation into nerve irritation, that is, in these receptors, a photon of light is transformed into an electrical impulse. Further, these impulses enter the central structures of the brain along the fibers of the optic nerve. Rods perceive mainly light in low visibility conditions, we can say that they are responsible for night perception. Due to the work of cones, a person has color perception and visual acuity. Now let's take a closer look at each group of photoreceptors.

Rod apparatus

Photoreceptors of this type resemble a cylinder in shape, the diameter of which is uneven, but the circumference is approximately the same. The length of the rod photoreceptor, which is 0.06 mm, is thirty times its diameter (0.002 mm). In this regard, this cylinder, rather, looks exactly like a stick. In the human eyeball, there are normally about 115-120 million rods.

Four segments can be distinguished in this type of photoreceptor:

• In the outer segment there are membrane discs;
• The connecting segment is an eyelash;
• The inner segment contains mitochondria;
• The basal segment is the nerve plexus.

The sensitivity of the sticks is very high, so the energy of even one photon is enough for them to produce an electrical impulse. It is this property that allows you to perceive surrounding objects in low light conditions. At the same time, the rods cannot distinguish colors due to the fact that in their structure there is only one type of pigment (rhodopsin). This pigment is also called visual purple. It contains two groups of protein molecules (opsin and chromophore), so there are also two peaks in the absorption curve of light waves. One of these peaks is located in the zone (278 nm) in which a person cannot perceive light (ultraviolet). The second maximum is located in the region of 498 nm, that is, on the border of the blue and green spectra.

It is known that the pigment rhodopsin, which is located in the rods, reacts to light waves much more slowly than iodopsin, which is in the cones. In this regard, the reaction of rods to the dynamics of light fluxes is also slower and weaker, that is, in the dark it is more difficult for a person to distinguish moving objects.

cone apparatus

The shape of cone photoreceptors, as you might guess, resembles laboratory flasks. Its length is 0.05 mm, the diameter at the narrow point is 0.001 mm, and at the wide point it is four times larger. The retina of the eyeball normally contains approximately seven million cones. By themselves, cones are less susceptible to light rays than rods, that is, their excitation requires tens of times more photons. However, cone photoreceptors process the received information much more intensively, and therefore it is easier for them to distinguish any dynamics of the light flux. This allows you to better perceive moving objects, and also determines the high visual acuity of a person.

There are also four elements in the structure of the cone:

• The outer segment, which consists of membrane discs with iodopsin;
• Connecting element represented by a constriction;
• The inner segment, which includes mitochondria;
• Basal segment responsible for the synaptic connection.

Cone photoreceptors can perform their functions, since they contain iodopsin. This pigment can be of different types, thanks to which a person is able to distinguish colors. Two types of pigment have already been isolated from the retina: erythrolab, which is particularly sensitive to red wavelengths, and chlorolab, which is highly sensitive to green light wavelengths. The third type of pigment, which should be sensitive to blue light, has not yet been isolated, but it is planned to call it cyanolab.

This (three-component) theory of color perception is based on the assumption that there are three types of cone receptors. Depending on what wavelength of light waves fall on them, a further formation of a color image occurs. However, in addition to the three-component theory, there is also a two-component nonlinear theory. According to her, each cone photoreceptor contains both types of pigment (chlorolab and erythrolab), that is, this receptor can perceive both green and red. The role of cyanolalab is played by rhodopsin faded from the sticks. In support of this hypothesis, one can cite the fact that people with color blindness (tritanopsia), who have lost color perception in the blue spectrum, have difficulty with twilight vision. This indicates a violation of the work of the rod apparatus.

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 dealt with 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, the main reason is 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 conditions, the noise amplitude 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 rod, 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 BUT 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. So 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 falling 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.

The human eye is one of the most complex organs responsible for the perception of all the surrounding information. Rods and cones play an important role in image formation, with the help of which light and color signals are converted into nerve impulses. Rods and cones are located on the retina of the eye, form a photosensory layer that forms and transmits an image to the brain. Thanks to them, a person distinguishes colors, can see in the dark.

Basic information about sticks

The shape of the rods in the eye resembles elongated rectangles, the length of which is approximately 0.06 mm. Each adult has more than 120 million rods, which are mostly located on the periphery of the retina. Receptors consist of the following layers:

• external with membranes containing a special pigment rhodopsin;
• a binder, represented by multiple cilia, transmitting signals from the external to the internal and vice versa;
• internal, which contains mitochondria designed for the production and redistribution of energy;
• basal, in which there are nerve fibers that transmit all impulses.

Rods located in the retina of the eye are light-sensitive elements responsible for night vision. They are not able to perceive colors, but they react even to a single photon. It is thanks to them that a person is able to see in the dark, but the image will be exclusively black and white.

The ability to perceive light even in the dark is provided by the pigment rhodopsin. When exposed to bright light, it "burns out", and responds only to short waves. After entering the darkness, the pigment is regenerated and captures even slight rays of light.

Basic data about cones

The cones are shaped like the chemical research vessels they are named after. These receptors are approximately 0.05 mm long and 0.004 mm wide. The average human eye has over seven million cones located mostly in the central part of the retina. They have low sensitivity to light rays, but they perceive the entire color gamut and quickly respond to moving objects.

The structure of cones includes the following segments:

• External, in which there are membrane folds filled with iodopsin pigment. This segment is constantly updated, providing full color vision.
• Internal, in which mitochondria are located and energy metabolism is carried out.
• Synaptic, which includes contacts (synapses) that transmit signals to the optic nerve.
• The constriction, which is a plasma-type membrane, through which energy flows from the inner segment to the outer. To do this, it has a huge number of microscopic cilia.

A full perception of the entire color gamut is provided by iodopsin, which in turn can be of several types:

• Erythrolab (L type) is responsible for the perception of long waves that transmit red-yellow shades.
• Chlorolab (M type) perceives medium waves characteristic of green-yellow shades.
• Cyanolab (S type) reacts exclusively to short wavelengths responsible for blue colors.

It is worth noting that the division of cones into three categories (three-component visual hypothesis) is not considered the only correct one. There is a theory that only two types of rhodopsin are present in cones - erythrolab and chlorolab, from which it follows that they are able to perceive only red, yellow and green shades. The blue color is transmitted with the help of burnt rhodopsin. In support of this theory, the fact that people suffering from tritanopia (lack of perception of the blue spectrum) additionally complain of difficulty with vision at night is used. And the so-called "night blindness" occurs when the rods dysfunction.

Diagnosis of the state of receptors

If there is a suspicion of malfunctioning of the rods and cones in the eye, then you should make an appointment with an ophthalmologist. The main signs of damage include:

• a sharp decrease in visual acuity;
• the appearance before the eyes of bright flashes, glare, butterflies and stars;
• deterioration of visual function at dusk;
• lack of color image;
• contraction of visual fields.

To establish an accurate diagnosis, you will need not only consultation with an ophthalmologist, but also the passage of specific studies. These include:

• Examination of the function of color perception using the 100-shade test or Ishihara charts.
• Ophthalmoscopy - examination of the fundus to determine the condition of the retina.
• Ultrasound examination of the eyeball.
• Perimetry - determination of visual fields.
• Hagiography of the fluorescent type, necessary for highlighting the vessels.
• Computer refractometry, which determines the refractive power of the eye.

After receiving the data, one of the diseases can be established. Most often diagnosed:

• Color blindness, in which there is an inability to distinguish colors of a certain spectrum.
• Hemeralopia or "night blindness" is a pathology in which a person is not able to see normally at dusk.
• Macular degeneration is an anomaly that affects the central part of the retina and leads to a rapid loss of visual acuity.
• Retinal detachment, which can provoke a huge number of diseases and external factors.
• Pigmentary retinal degeneration is a hereditary pathology that leads to serious visual impairment.
• Chorioretinitis is an inflammatory process that affects all layers of the retina.

Violations in the work of cones and rods can be provoked by trauma, as well as advanced inflammatory eye diseases, general severe infectious diseases.

Cones and rods belong to the receptor apparatus of the eyeball. They are responsible for the transmission of light energy by transforming it into a nerve impulse. The latter passes along the fibers of the optic nerve to the central structures of the brain. Rods provide vision in low light conditions, they are able to perceive only light and dark, that is, black and white images. Cones are able to perceive different colors, they are also an indicator of visual acuity. Each photoreceptor has a structure that allows it to perform its functions.

Structure of rods and cones

The sticks are shaped like a cylinder, which is why they got their name. They are divided into four segments:

• Basal, connecting nerve cells;
• A binder that provides a connection with the cilia;
• Outer;
• Internal, containing mitochondria that produce energy.

The energy of one photon is enough to excite the rod. This is perceived by a person as light, which allows him to see even in very low light conditions.

The rods have a special pigment (rhodopsin) that absorbs light waves in the region of two ranges.
Cones are similar in appearance to flasks, which is why they have their name. They contain four segments. Inside the cones is another pigment (iodopsin), which provides the perception of red and green colors. The pigment responsible for blue color recognition has not yet been identified.

Physiological role of rods and cones

Cones and rods perform the main function, which is to perceive light waves and transform them into a visual image (photoreception). Each receptor has its own characteristics. For example, sticks are needed in order to see at dusk. If for some reason they cease to perform their function, a person cannot see in low light conditions. Cones are responsible for clear color vision in normal light.

In another way, we can say that the rods belong to the light-perceiving system, and the cones - to the color-perceiving system. This is the basis for differential diagnosis.

Video about the structure of rods and cones

Symptoms of rod and cone damage

In diseases accompanied by damage to rods and cones, the following symptoms occur:

• Decreased visual acuity;
• The appearance of flashes or glare before the eyes;
• Decreased twilight vision;
• Inability to distinguish colors;
• Narrowing of the visual fields (in extreme cases, the formation of tubular vision).

Some diseases have very specific symptoms that make it easy to diagnose pathology. This applies to hemeralopia or. Other symptoms may be present in various pathologies, and therefore it is necessary to conduct an additional diagnostic examination.

Diagnostic methods for rod and cone lesions

To diagnose diseases in which there is a lesion of rods or cones, it is necessary to perform the following examinations:

• with state definition ;
• (study of visual fields);
• Diagnosis of color perception using Ishihara tables or a 100-shade test;
• Ultrasound procedure;
• Fluorescent hagiography, which provides visualization of blood vessels;
• Computer refractometry.

It is worth recalling once again that photoreceptors are responsible for color perception and light perception. Due to work, a person can perceive an object, the image of which is formed in the visual analyzer. With pathologies

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 - cones experience an increased load. The rods are responsible for twilight vision - if they are not active enough, night blindness appears.

Cones and rods in the retina of the eye have a different structure, since their functions are different.

The cornea is a transparent membrane with blood vessels and nerve endings, bordering on the sclera, located on the front of the organ of vision. The anterior chamber, between the cornea and the iris, contains intraocular fluid. The iris is the area of ​​the eye with the opening for the pupil. Its structure: muscles that change the diameter of the pupil with changes in lighting and regulate the flow of light. The pupil is the hole through which light passes into the eye. The lens is an elastic transparent lens that can instantly adjust to visual images - change focus to assess the size of objects and the distance to them. The vitreous body is an absolute transparent substance of a gel-like consistency, thanks to which the eye has a spherical shape. Performs an exchange function in the organ of vision. The retina - consists of 3 layers, is responsible for vision and color perception, it includes blood vessels, nerve fibers and high sensitivity photoreceptors. It is thanks to the similar structure of the retina that impulses enter the brain, which arise as a result of the perception of light waves of different lengths. Thanks to this ability of the retina, a person distinguishes between primary colors and their numerous shades. Different types of people have different color sensitivity. The sclera is the outer layer of the eye that extends into the cornea.

The organ of vision also includes the 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 in the 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 the yellow spot of the eye. 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 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 in the perception of 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 region.

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.

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 of the optic nerve. In the daytime, the sensitivity of the eye shifts to the blue area, at 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.

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

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 a "calming" effect on the other, which increases the sharpness of information perception.

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.

Vision is one of the ways to know the world around us and navigate in space. Despite the fact that other senses are also very important, with the help of the eyes, a person perceives about 90% of all information coming from the environment. Thanks to the ability to see what is around us, we can judge the events taking place, distinguish objects from each other, and also notice threatening factors. Human eyes are arranged in such a way that in addition to the objects themselves, they also distinguish the colors in which our world is painted. Special microscopic cells are responsible for this - rods and cones, which are present in the retina of each of us. Thanks to them, the information we perceive about the type of surroundings is transmitted to the brain.

The structure of the eye: diagram

Despite the fact that the eye takes up so little space, it contains many anatomical structures, thanks to which we have the ability to see. The organ of vision is almost directly connected with the brain, and with the help of a special study, ophthalmologists see the intersection of the optic nerve. The eyeball has the shape of a ball and is located in a special recess - the orbit, which is formed by the bones of the skull. To understand why the numerous structures of the organ of vision are needed, it is necessary to know the structure of the eye. The diagram shows that the eye consists of such formations as the vitreous body, the lens, the anterior and posterior chambers, the optic nerve and membranes. Outside, the organ of vision is covered by the sclera - the protective frame of the eye.

Shells of the eye

The sclera performs the function of protecting the eyeball from damage. It is the outer shell and occupies about 5/6 of the surface of the organ of vision. The part of the sclera that is outside and goes directly to the environment is called the cornea. It has properties due to which we have the ability to clearly see the world around us. The main ones are transparency, specularity, moisture, smoothness and the ability to transmit and refract rays. The rest of the outer shell of the eye - the sclera - consists of a dense connective tissue base. Under it is the next layer - the vascular. The middle shell is represented by three formations located in series: the iris, the ciliary (ciliary) body and the choroid. In addition, the vascular layer includes the pupil. It is a small hole that is not covered by the iris. Each of these formations has its own function, which is necessary to ensure vision. The last layer is the retina of the eye. It communicates directly with the brain. The structure of the retina is very complex. This is due to the fact that it is considered the most important shell of the organ of vision.

The structure of the retina

The inner shell of the organ of vision is an integral part of the medulla. It is represented by layers of neurons that line the inside of the eye. Thanks to the retina, we get an image of everything that is around us. All refracted rays are focused on it and are composed into a clear object. Nerve cells in the retina pass into the optic nerve, along the fibers of which information reaches the brain. There is a small spot on the inner shell of the eye, which is located in the center and has the greatest ability to see. This part is called the macula. In this place are visual cells - rods and cones of the eye. They provide us with both day and night vision of the world around us.

Functions of rods and cones

These cells are located on the retina of the eye and are essential for seeing. Rods and cones are converters of black and white and color vision. Both types of cells act as light-sensitive receptors in the eye. The cones are so named because of their conical shape, they are the link between the retina and the central nervous system. Their main function is the conversion of light sensations received from the external environment into electrical signals (impulses) processed by the brain. Specificity for daylight recognition belongs to cones due to the pigment they contain - iodopsin. This substance has several types of cells that perceive different parts of the spectrum. The rods are more sensitive to light, so their main function is more difficult - providing visibility at dusk. They also contain a pigment base - the substance rhodopsin, which discolors when exposed to sunlight.

Structure of rods and cones

These cells got their name due to their shape - cylindrical and conical. Rods, unlike cones, are located more along the periphery of the retina and are practically absent in the macula. This is due to their function - providing night vision, as well as peripheral fields of vision. Both types of cells have a similar structure and consist of 4 parts:

The outer segment - it contains the main pigment of the rod or cone, covered with a shell. Rhodopsin and iodopsin are in special containers - disks.
The cilium is a part of the cell that provides the relationship between the outer and inner segments. Mitochondria - they are necessary for energy metabolism. In addition, they contain EPS and enzymes that ensure the synthesis of all cellular components. All this is in the inner segment. Nerve endings.

The number of photosensitive receptors on the retina varies greatly. Rod cells make up about 130 million. The cones of the retina are significantly inferior to them in number, on average there are about 7 million of them.

Features of the transmission of light pulses

Rods and cones are able to perceive the light flux and transmit it to the central nervous system. Both types of cells are able to work during the daytime. The difference is that cones are much more sensitive to light than rods. The transmission of the received signals is carried out thanks to interneurons, each of which is attached to several receptors. Combining several rod cells at once makes the sensitivity of the organ of vision much greater. This phenomenon is called "convergence". It provides us with an overview of several fields of vision at once, as well as the ability to capture various movements occurring around us.

The ability to perceive colors

Both types of retinal receptors are necessary not only to distinguish between day and twilight vision, but also to determine color pictures. The structure of the human eye allows a lot: to perceive a large area of ​​the environment, to see at any time of the day. In addition, we have one of the interesting abilities - binocular vision, which allows us to significantly expand the field of view. Rods and cones are involved in the perception of almost the entire color spectrum, due to which people, unlike animals, distinguish all the colors of this world. Color vision is largely provided by cones, which are of 3 types (short, medium and long wavelengths). However, rods also have the ability to perceive a small part of the spectrum.