Photosensitivity in rods. Light sensitivity

The very front 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 ultraviolet rays. If there is a lot of melanin, then the eyes turn out brown, if the average amount is green, if there is little, they turn out blue.

The lens is located behind the pupil. This 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 relaxes, the ligaments holding the lens tighten and it becomes flat, the eye focuses on distant objects. This property of the eye is called accommodation.

Located behind the lens vitreous, filling the eyeball from the inside. This is the third and final component of the refractive system of the eye (cornea - lens - vitreous).

For vitreous, on inner surface eyeball the retina is located. It consists of visual receptors - rods and cones. Under the influence of light, receptors are excited and transmit information to the brain. The rods are located mainly on the periphery of the retina; they provide only a black and white image, but they only need low lighting (they can work in the twilight). The visual pigment of the rods is rhodopsin, a derivative of vitamin A. The cones are concentrated in the center of the retina, they produce a color image and 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 (it has no receptors at all, it comes out of this place optic nerve).

Behind the retina ( retina eyes, the innermost) is located choroid(average). It contains blood vessels, nourishing the eye; in the front part it changes into iris and ciliary muscle.

For choroid located tunica albuginea, covering the outside of the eye. It performs a protective function; in the front part of the eye it is modified into the cornea.

Choose the one that suits you best correct option. The function of the pupil in the human body is
1) focusing light rays onto the retina
2) regulation of luminous flux
3) transformation 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) tunica albuginea
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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

5. Establish the sequence of processes of passage of a ray 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 light beam by the lens
4) transmission of nerve impulses along the optic nerve
5) passage of light rays through the cornea

Answer

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

Answer

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

Answer

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

Answer

The refraction of rays in the eyeball is carried out using
1) blind spot
2) macular spot
3) pupil
4) lens

Answer

1. Select three correctly labeled captions for the drawing “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 “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 labeled captions for the picture that 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. Select three correctly labeled captions for the picture that depicts 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 visual receptors and their characteristics: 1) cones, 2) rods. Write numbers 1 and 2 in the correct order.
A) perceive colors
B) active in good lighting
B) visual pigment rhodopsin
D) exercise black-and-white vision
D) contain the pigment iodopsin
E) distributed evenly across the retina

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. The 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 continuously move, providing
1) prevention of eye blindness
2) transmission of impulses along the optic nerve
3) the direction of light rays to the macula of the retina
4) perception of visual stimuli

Answer

Choose one, the most correct option. Human vision depends on the condition 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 membranes of the eyeball: 1) albuginea, 2) vascular, 3) retina. Write 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 the iris
D) protects the eyeball from external influences
E) contains a blind spot

Answer

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

Retinal rods

These photoreceptors are cylindrical in shape, with a length of approximately 0.06 mm and a diameter of approximately 0.002 mm. Thus, such a cylinder is really quite similar to a stick. Eye healthy person contains approximately 115-120 million rods.

The human eye rod can be divided into 4 segmental zones:

1 - Outer segmental zone (includes membranous discs containing rhodopsin),
2 - Connecting segmental zone (cilium),

4 - Basal segmental zone (nerve connection).

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.

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 range of light visible to the human eye (278 nm - the region of ultraviolet radiation), 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 reliably known that rhodopsin, present in rods, reacts to light much more slowly than iodopsin, contained in cones. Therefore, rods are characterized by a weak reaction to the dynamics of light fluxes, and in addition, they poorly distinguish 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 the narrowest point is approximately 0.001 mm, and at the widest point it is 0.004. The retina of a healthy adult contains about 7 million cones.

Cones have less sensitivity to light. That is, to excite their activity, a luminous flux will be required, which is tens of times more intense than to excite the work of rods. But cones process light fluxes much more intensely than rods, so they perceive their changes better (for example, they better distinguish light when objects move, in dynamics relative to the eye). They also define images more clearly.

Cones human eye, also include 4 segmental zones:

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

The reason for the above-described properties of cones is the content of the 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), and 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 type of dominance of color pigment in them (erythrolab, chlorolab, cyanolab) is due to the three-component vision hypothesis. There is, however, another theory of vision - nonlinear two-component. Its adherents believe that all cones contain erythrolab and chlorolab at the same time, and therefore are able to perceive colors in both the red and green spectrum. The role of cyanolabe, in this case, is played by the faded rhodopsin of the rods. This theory is also confirmed by examples of people suffering from the inability to distinguish the blue part of the spectrum (tritanopia). They also have difficulty with twilight vision (

Hello, dear readers! We have all heard that eye health should be protected from a young age, because lost vision cannot always be restored. 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 consisting of nerve tissue and vessels. But it is he who is entrusted most important function to process the information received by the eye into nerve impulses, allowing the brain to create a color three-dimensional image.

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

Rods and cones

Both of these elements with funny names– photoreceptors that produce an image recorded by the lens and parts of the cornea.

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

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

They consist of:

membrane disks;
nervous tissue;
mitochondria.

They are also provided with eyelashes. A special pigment, the protein rhodopsin, allows cells to “sense” light.

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

Differences between the photoreceptors of the eye

The differences start from the location. The “jugs” are “crowded” closer to the center. They are "responsible" for central vision. In the center of the retina, in the so-called " macula", there are especially many of them.

The density of the cluster of “cylinders,” on the contrary, is higher towards the periphery of the eye.

You can also note the following features:

cones contain less photopigment than rods;
the total number of “cylinders” is 2 dozen times more;
rods are able to perceive any light - diffused and direct; and the cones are exclusively 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: he sees even up to a million shades of colors!

Interesting fact: in order to transmit impulses, several rods require only one neuron. Cones are “more demanding”: each requires its own neuron.

“Cylinders” are highly sensitive; “jugs” need stronger light pulses so that they can perceive and transmit them.

Essentially, thanks to them we can see in the dark. In low light conditions (late evening, at night), cones cannot “work.” But the sticks begin to operate in full force. And since they are located on the periphery, in the dark we better perceive movements not directly in front of us, but on the sides.

Yes, and one more thing: sticks react faster.

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

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

By absorbing light quanta, cells convert energy into a nerve impulse. It enters the brain. The result is that we see the world!

Why cats see better than us in the dark

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

The casket opens simply: the structure of the eye of this mammal is similar to that of a human. But if a person has about 4 rods per 1 cone, then a cat has 25! It is not surprising that the 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 can see well in the light and can navigate in the dark.

If they cease to perform their functions in full, the following are observed:

light glare in front of the eyes;
decreased visibility in the dark;
the fields of vision become narrower.

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

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

Did you find benefit from our article? If you have a little less questions related to the structure and functioning of the visual organs, we can consider our task completed. And one more thing: please share the information you receive 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 of the eye. They convert light stimulation into nervous stimulation, that is, in these receptors the transformation of a photon of light into an electrical impulse occurs. These impulses then enter central structures brain along the fibers of the optic nerve. Rods primarily perceive 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 are shaped like a cylinder, 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 greater than its diameter (0.002 mm). In this regard, this cylinder, rather, looks exactly like a stick. There are normally about 115-120 million rods in the human eyeball.

This type of photoreceptor can be divided into four segments:

The outer segment contains membrane discs;
The connecting segment is a cilium;
The inner segment contains mitochondria;
The basal segment is a nerve plexus.

The sensitivity of the rods 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, rods cannot distinguish colors due to the fact that their structure contains 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 in the zone (278 nm) in which humans 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 rods, reacts to light waves much more slowly than iodopsin, which is located in cones. In this regard, the reaction of the 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, its diameter at the narrow point is 0.001 mm, and at the wide point it is four times larger. The normal retina of the eyeball contains approximately seven million cones. The cones themselves are less susceptible 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.

The cone structure also has four elements:

The outer segment, which consists of membrane disks with iodopsin;
A connecting element represented by a constriction;
The inner segment, which contains mitochondria;
Basal segment responsible for synaptic connection.

Cone photoreceptors can perform their functions because they contain iodopsin. This pigment may be 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 especially sensitive to waves from the red spectrum, and chlorolab, which has high sensitivity to the green waves of light. The third type of pigment that should be sensitive to blue light, has not yet been isolated, but it is planned to call it cyanolabe.

This (three-component) theory of color perception is based on the assumption that there are three types of cone receptors. Depending on the length of light waves that hit them, further formation color image. However, in addition to the three-component theory, there is also a two-component nonlinear theory. According to it, each cone photoreceptor contains both types of pigment (chlorolab and erythrolab), that is, this receptor can perceive both green and red colors. The role of cyanolabe is played by rhodopsin, faded from the rods. Supporting this hypothesis is the fact that people with color blindness (tritanopsia), who have lost color vision in the blue spectrum, have difficulty seeing at night. This indicates a malfunction of the rod apparatus.

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 environment. Thanks to the ability to see what is around us, we can judge current events, distinguish objects from each other, and also notice threatening factors. Human eyes are designed 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 appearance of our surroundings is transmitted to the brain.

Structure of the eye: diagram

Even though the eye takes up so little space, it contains many anatomical structures that give us the ability to see. The organ of vision is almost directly connected to the brain, and with the help special research ophthalmologists see the intersection of the optic nerve. It 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, you need to know the structure of the eye. The diagram shows that the eye consists of such formations as the lens, anterior and posterior chambers, optic nerve and membranes. The outside of the organ of vision is covered by the sclera - the protective frame of the eye.

Eye shells

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 on the outside and extends directly to the surrounding 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, humidity, smoothness and the ability to transmit and refract rays. The rest of the outer layer of the eye - the sclera - consists of a dense connective tissue base. Below it is the next layer - the vascular layer. The middle shell is represented by three formations located sequentially: the iris and the choreoid. In addition, the vascular layer includes the pupil. It is a small hole not covered by the iris. Each of these formations has its own function, which is necessary for vision. The last layer is the retina of the eye. It contacts 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 membrane 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 formed into a clear object. The retina passes into the optic nerve, through 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 greatest ability to the vision. This part is called the macula. In this place are located the visual cells - the 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 necessary in order to see. Rods and cones are the 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 connecting link between the retina and the central nervous system. Their main function is the transformation of light sensations obtained from external environment, into electrical signals (impulses) processed by the brain. Cones are specific for daylight recognition 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 - ensuring 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 visual fields. Both types of cells have a similar structure and consist of 4 parts:

The number of light-sensitive receptors on the retina varies greatly. Rod cells number about 130 million. The cones of the retina are significantly inferior to them in number, on average there are approximately 7 million of them.

Features of the transmission of light pulses

Rods and cones are capable of receiving light and transmitting it to the central nervous system. Both types of cells are capable of working in daytime. The difference is that the light sensitivity of cones is much higher than that of rods. The transmission of received signals is carried out thanks to interneurons, each of which is attached to several receptors. The combination of 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.

Ability to perceive colors

Both types of retinal receptors are necessary not only to distinguish between daytime and twilight vision, but also to identify color pictures. The structure of the human eye allows many things: to perceive large area environment, visible at any time of the day. In addition, we have one of the interesting abilities - binocular vision, allowing you to significantly expand your overview. Rods and cones are involved in the perception of almost the entire color spectrum, thanks to which people, unlike animals, distinguish all the colors of this world. Color vision To a greater extent, they are provided by cones, which come in 3 types (short, medium and long wavelength). However, rods also have the ability to perceive a small part of the spectrum.