Light sensitivity in rods. Light sensitivity

The most anterior part of the eye is called the cornea. It is transparent (transmits light) and convex (refracts light).

Behind the cornea is Iris, in the center of which there is a hole - the pupil. The iris is made up of muscles that can change the size of the pupil and thus regulate the amount of light entering the eye. The iris contains the pigment melanin, which absorbs harmful ultra-violet rays. If there is a lot of melanin, then the eyes turn brown, if the average amount is green, if there is little, blue.

Behind the pupil is the lens. It is a transparent capsule filled with liquid. Due to its own elasticity, the lens tends to become convex, while the eye focuses on close objects. When the ciliary muscle is relaxed, the ligaments holding the lens are stretched and it becomes flat, the eye focuses on distant objects. This property of the eye is called accommodation.

Behind the lens is vitreous body filling the eyeball from the inside. This is the third and last component of the refractive system of the eye (cornea - lens - vitreous body).

Per vitreous body, on the inner surface eyeball the retina is located. It consists of visual receptors - rods and cones. Under the action of light, receptors are excited and transmit information to the brain. The rods are located mainly on the periphery of the retina, they give only a black and white image, but they have enough low light (they can work at dusk). The visual pigment of the rods is rhodopsin, a derivative of vitamin A. The cones are concentrated in the center of the retina, they give a color image, they require bright light. There are two spots in the retina: yellow (it contains the most high concentration cones, the place of greatest visual acuity) and blind (there are no receptors in it at all, optic nerve).

Behind the retina ( retina eyes, innermost) is located choroid(medium). It contains blood vessels that nourish the eye; at the front, it changes into iris and ciliary muscle.

Per choroid situated albuginea covering the outside of the eye. It performs the function of protection, in front of the eye it is modified into the cornea.

Choose the one most correct option. The function of the pupil in the human body is to
1) focusing light rays on the retina
2) regulation of the luminous flux
3) conversion of light stimulation into nervous excitement
4) color perception

Answer

Choose one, the most correct option. A black pigment that absorbs light is located in the human organ of vision in
1) blind spot
2) choroid
3) protein shell
4) vitreous body

Answer

Choose one, the most correct option. The energy of light rays entering the eye causes nervous excitement
1) in the lens
2) in the vitreous body
3) in visual receptors
4) in the optic nerve

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Choose one, the most correct option. Behind the pupil in the human organ of vision is located
1) choroid
2) vitreous body
3) lens
4) retina

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1. Set the path of the light beam in the eyeball
1) pupil
2) vitreous body
3) retina
4) lens

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2. Establish the sequence of passage of the light signal to the visual receptors. Write down the corresponding sequence of numbers.
1) pupil
2) lens
3) vitreous body
4) retina
5) cornea

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3. Establish the sequence of location of the structures of the eyeball, starting with the cornea. Write down the corresponding sequence of numbers.
1) retinal neurons
2) vitreous body
3) the pupil in the pigment membrane
4) light sensitive rod cells and cones
5) convex transparent part of the albuginea

Answer

4. Set the sequence of signals passing through the touch visual system. Write down the corresponding sequence of numbers.
1) optic nerve
2) retina
3) vitreous body
4) lens
5) cornea
6) visual area of the cerebral cortex

Answer

5. Establish the sequence of processes for the passage of a beam of light through the organ of vision and a nerve impulse in visual analyzer. Write down the corresponding sequence of numbers.
1) converting a beam of light into nerve impulse in the retina
2) information analysis
3) refraction and focusing of a beam of light by the lens
4) transmission of a nerve impulse along the optic nerve
5) the passage of light rays through the cornea

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Choose one, the most correct option. The light-sensitive receptors of the eye - rods and cones - are in the shell
1) rainbow
2) protein
3) vascular
4) mesh

Answer

1. Choose the three correct options: the refractive structures of the eye include:
1) cornea
2) pupil
3) lens
4) vitreous body
5) retina
6) yellow spot

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2. Choose three correct answers from six and write down the numbers under which they are indicated. Optical system the eye is made up of
1) lens
2) vitreous body
3) optic nerve
4) yellow spots of the retina
5) cornea
6) albuginea

Answer

Refraction of rays in the eyeball is carried out with the help of
1) blind spot
2) yellow spot
3) pupil
4) lens

Answer

1. Select three correctly labeled captions for the figure "Structure of the eye". Write down the numbers under which they are indicated.
1) cornea
2) vitreous body
3) iris
4) optic nerve
5) lens
6) retina

Answer

2. Select three correctly labeled captions for the drawing “The structure of the eye”. Write down the numbers under which they are indicated.
1) iris
2) cornea
3) vitreous body
4) lens
5) retina
6) optic nerve

Answer

3. Choose three correctly marked captions for the figure, which shows internal structure organ of vision. Write down the numbers under which they are indicated.
1) pupil
2) retina
3) photoreceptors
4) lens
5) sclera
6) yellow spot

Answer

4. Choose three correctly labeled captions for the drawing, which shows the structure of the human eye. Write down the numbers under which they are indicated.
1) retina
2) blind spot
3) vitreous body
4) sclera
5) pupil
6) cornea

Answer

Establish a correspondence between the visual receptors and their features: 1) cones, 2) rods. Write the numbers 1 and 2 in the correct order.
A) perceive colors
B) active in good light
B) visual pigment rhodopsin
D) exercise black and white vision
D) contain the pigment iodopsin
E) evenly distributed over the retina

Answer

Choose three correct answers from six and write down the numbers under which they are indicated. Differences between human daytime vision and twilight vision are that
1) cones work
2) color discrimination is not carried out
3) visual acuity is low
4) sticks work
5) color discrimination is carried out
6) visual acuity is high

Answer

Choose one, the most correct option. When viewing an object, a person's eyes move continuously, providing
1) eye glare prevention
2) transmission of impulses along the optic nerve
3) the direction of light rays to the yellow spot of the retina
4) perception of visual stimuli

Answer

Choose one, the most correct option. Human vision depends on the state of the retina, since it contains light-sensitive cells in which
1) vitamin A is formed
2) visual images arise
3) black pigment absorbs light rays
4) nerve impulses are formed

Answer

Establish a correspondence between the characteristics and the membranes of the eyeball: 1) protein, 2) vascular, 3) retina. Write down the numbers 1-3 in the order corresponding to the letters.
A) contains several layers of neurons
B) contains pigment in cells
B) contains the cornea
D) contains an iris
D) protects the eyeball from external influences
E) contains a blind spot

Answer

Rods and cones are light-sensitive receptors in the eye, also called photoreceptors. Their main task is to convert light stimuli into nervous ones. That is, it is they who turn light rays into electrical impulses that enter the brain along, which, after a certain processing, become the images we perceive. Each type of photoreceptor has its own task. Rods are responsible for light perception in low light conditions (night vision). The cones are responsible for visual acuity, as well as color perception (daytime vision).

retinal rods

These photoreceptors are cylindrical in shape, about 0.06 mm long and about 0.002 mm in diameter. Thus, such a cylinder is indeed very similar to a stick. Eye healthy person contains approximately 115-120 million sticks.

The wand of the human eye can be divided into 4 segmental zones:

1 - Outer segmental zone (includes membrane discs containing rhodopsin),
2 - Connecting segmental zone (eyelash),

4 - Basal segmental zone (nerve connection).

The rods are highly photosensitive. So, for their reaction, the energy of 1 photon (the smallest, elementary particle of light) is enough. This fact is very important for night vision, which allows you to see in low light.

The rods cannot distinguish colors, this is primarily due to the presence of only one pigment in them - rhodopsin. The pigment rhodopsin, otherwise called visual purple, due to the included protein groups (chromophores and opsins) has 2 light absorption maxima. True, one of the maxima exists beyond the light visible to the human eye (278 nm - the UV radiation region), therefore, it is probably worth calling it the wave absorption maximum. But, the second maximum is visible to the eye - it exists at around 498 nm, located on the border of green and blue color spectrum.

It is well known that rhodopsin present in rods reacts to light much more slowly than iodopsin contained in cones. Therefore, sticks are characterized by a weak reaction to the dynamics of light fluxes, and in addition, they poorly distinguish between the movements of objects. And visual acuity is not their prerogative.

Cones of the retina

These photoreceptors also get their name from characteristic form similar to the shape of laboratory flasks. The length of the cone is approximately 0.05 mm, its diameter at its narrowest point is approximately 0.001 mm, and at its widest point it is 0.004 mm. The retina of a healthy adult contains about 7 million cones.

Cones are less sensitive to light. That is, to excite their activity, a light flux is required, which is ten times more intense than to excite the work of the sticks. But cones process light fluxes much more intensively than rods, so they perceive their changes better (for example, they better distinguish light when objects move, in dynamics relative to the eye). In addition, they define images more clearly.

cones human eye, also include 4 segmental zones:

1 - Outer segmental zone (includes membrane discs containing iodopsin),
2 - Connecting segmental zone (constriction),
3 - Inner segmental zone (includes mitochondria),
4 - Zone of synaptic connection or basal segment.

The reason for the above properties of cones is the content of a specific pigment, iodopsin, in them. Today, 2 types of this pigment have been isolated and proven: erythrolab (iodopsin, sensitive to the red spectrum and long L-waves), as well as chlorolab (iodopsin, sensitive to the green spectrum and medium M-waves). A pigment that is sensitive to the blue spectrum and short S-waves has not yet been found, although the name has already been assigned to it - cyanolab.

The division of cones according to the types of dominance of the color pigment in them (erythrolab, chlorolab, cyanolab) is due to the three-component hypothesis of vision. There is, however, another theory of vision - a non-linear two-component one. Its adherents believe that all cones include erythrolab and chlorolab at the same time, and therefore are able to perceive colors of both the red and green spectrum. The role of cyanolalab, in this case, is performed by the faded rhodopsin of the rods. This theory is also confirmed by examples of people suffering, namely the inability to distinguish the blue part of the spectrum (tritanopia). They also have difficulty with twilight vision (

Hello, dear readers! We all have heard that eye health should be protected from a young age, because lost vision cannot always be returned. Have you ever thought about how the eye works? If we know this, then it will be easier for us to understand what processes provide visual perception of the world around us.

The human eye has a complex structure. Perhaps the most mysterious and complex element is the retina. This is a thin layer of nervous tissue and vessels. But it is on him that essential function processing the information received by the eye into nerve impulses, allowing the brain to create a color three-dimensional picture.

Today we will talk about the receptors of the nervous tissue of the retina - namely, the rods. What is the light sensitivity of the retinal rod receptors and what allows us to see in the dark?

Rods and cones

Both of these elements are funny names- photoreceptors that give an image fixed by the lens and parts of the cornea.

There are a lot of those and others in the human eye. Cones (they look like tiny jugs) - about 7 million, and rods ("cylinders") even more - up to 120 million! Of course, their dimensions are negligible and amount to fractions of millimeters (µm). The length of one stick is 60 microns. The cones are even smaller - 50 microns.

The sticks got their name due to their shape: they resemble microscopic cylinders.

They consist of:

membrane disks;
nervous tissue;
mitochondria.

And they are provided with cilia. A special pigment - the protein rhodopsin - allows cells to "feel" light.

Rhodopsin (this is a protein plus a yellow pigment) reacts to a beam of light in the following way: under the action of light pulses, it decomposes, thus causing irritation of the optic nerve. I must say, the susceptibility of the "cylinders" is amazing: they capture information even from 2 photons!

Differences between photoreceptors in the eye

The differences start with the location. "Jugs" "crowd" closer to the center. They are "responsible" for central vision. In the center of the retina, in the so-called " yellow spot", there are a lot of them.

The density of the accumulation of "cylinders", on the contrary, is higher towards the periphery of the eye.

In addition, the following features can be noted:

cones contain less photopigment than rods;
the total number of "cylinders" is 2 dozen times greater;
sticks are able to perceive any light - diffused and direct; and the cones are exceptionally straight;
with the help of cells located on the periphery, we perceive black and white colors(they are achromatic);
with the help of those gathering in the center - all colors and shades (they are chromatic).

Each of us is able, thanks to the "jugs" to see up to a thousand shades. And the artist's eye is even more sensitive: it sees even up to a million shades of colors!

An interesting fact: in order to carry out the transmission of impulses, several rods require only one neuron. Cones are "more demanding": each needs its own neuron.

"Cylinders" are highly sensitive, "jugs" need stronger light pulses so that they can perceive and transmit them.

In fact, thanks to them we can see in the dark. In conditions of reduced illumination (late in the evening, at night), cones cannot "work". But the sticks begin to act in full force. And since they are located on the periphery, in the dark we better catch movements not directly in front of us, but on the sides.

Oh, and one more thing: sticks react faster.

Take note: when going somewhere in the dark, do not try to stare at the area directly in front of your eyes. You won’t see anything anyway, because the “jugs” located in the center of the retina are now powerless. But if you “turn on” peripheral vision, you will be able to navigate much better. It is the "cylinders" that "work".

Despite the significant difference in the performance of the tasks set by nature, photoreceptors cannot be considered separately from each other. Only together they give a single holistic picture.

By absorbing light quanta, the cells convert the energy into a nerve impulse. It goes to the brain. The result - we see the world!

Why do cats see us better in the dark?

Now, having studied in general terms the structure and functions of photoreceptors, we can answer the question of why our mustachioed pets are much better at navigating in the dark than we are.

The casket opens simply: the structure of the eye of this mammal is similar to a human one. But if a person has about 4 rods per 1 cone, then a cat has 25! It is not surprising that a domestic predator perfectly distinguishes the outlines of objects in almost complete darkness.

Rods and cones are our helpers

"Cylinders" and "jugs" are an amazing invention of nature. If they function correctly, a person sees well in the light and can navigate in the dark.

If they cease to perform their functions in full, there are:

light glare before the eyes;
deterioration of visibility in the dark;
are already in the field of view.

Over time, visual acuity changes for the worse. Color blindness, hemeralopia (decreased night vision), retinal detachment - these are the consequences of a violation of the photoreceptors.

But let's not end our conversation on that sad note. modern medicine learned to cope with most of the diseases that previously caused blindness. The patient is required only an annual preventive examination.

Did you find any benefit in our article? If you have a little less questions related to the structure and work of the organs of vision, we can consider our task completed. And one more thing: please share the received information with your friends, and you can send us your comments and remarks. We are waiting for responses. Your feedback is always welcome!

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. These impulses are then sent to central structures 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. The cones themselves are less receptive to light rays than the rods, that is, it takes tens of times to excite them. more quantity 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 may be different types which makes it possible for humans to distinguish colors. Two types of pigment have already been isolated from the retina of the eye: erythrolab, which is especially sensitive to waves from the red spectrum, and chlorolab, which has high sensitivity to green waves of light. The third type of pigment, which must 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 hit them, there is further formation color image. However, in addition to the three-component theory, there is also a two-component theory. 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.

Vision is one way to know the world 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 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 special study Ophthalmologists see the intersection of the optic nerve. has the shape of a ball and is located in a special recess - an 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 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 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 lining of the organ of vision is an integral part 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. The retinas pass into the optic nerve, through the fibers of which information reaches the brain. On the inner shell of the eye there is a small spot, which is located in the center and has greatest ability to the vision. 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 eyes and are essential in order to see. Rods and cones are converters of black and white and color vision. Both types of cells act as photosensitive receptors eyes. 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 transformation of light sensations received from external environment, into electrical signals (impulses) processed by the brain. Specificity to recognize daylight belongs to cones due to the pigment they contain - iodopsin. This substance has several types of cells that perceive different parts of the spectrum. 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 becomes discolored 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 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 in 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 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 daylight and twilight vision, but also to identify color pictures. The structure of the human eye allows a lot: to perceive large area environment, see at any time of the day. In addition, we have one of the interesting abilities - binocular vision, allowing you to significantly expand the overview. 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 to a greater extent provide cones, which are of 3 types (short, medium and long wavelength). However, rods also have the ability to perceive a small part of the spectrum.