Refracting rays. The lens has the ability to change curvature, while it acts as an autofocus, which allows you to very quickly change from near to distant objects. The retina, similar to photographic film or the matrix of a digital camera, captures the received data, which is then transmitted to the central structures of the brain for further analysis.
Complex anatomical structure the eye is a very delicate mechanism and is subject to various external influences and pathologies that arise against the background of impaired metabolism or diseases of other body systems.
The human eye is a paired organ whose structure is very complex. Thanks to the work of this organ, a person receives most (about 90%) of information about the outside world. Despite its thin and complex structure, the eye is amazingly beautiful and individual. However, there are also common features in its structure that are important for performing basic functions optical system. During the process of evolutionary development, significant changes occurred in the eye and, as a result, tissues of various origins (nerves, connective tissue, blood vessels, pigment cells, etc.) found their place in this unique organ.
The shape of the eye is similar to a sphere or ball, which is why this organ is also called the eyeball. Its structure is quite delicate, and therefore nature has programmed the intraosseous location of the eye. The cavity reliably protects the eye from external physical influences. Front eyeball covered (upper and lower). To ensure the mobility of the eye, there are several paired muscles that work precisely and harmoniously to provide binocular vision.
To keep the surface of the eye moist all the time, liquid is constantly secreted, which forms a thin film on the surface of the cornea. The excess flows into the lacrimal ducts.
The conjunctiva is the outermost membrane. In addition to the eyeball itself, it covers the inner surface of the eyelids.
Due to the pigment in the iris, people have different eye colors. The amount of pigment determines the color of the iris, which can be pale blue or dark brown. In the central zone of the iris there is an opening called the pupil. Through it, light rays penetrate into the eyeball and hit the retina. It is interesting that the iris and the choroid proper are innervated and supplied with blood from different sources. This is reflected in many pathological processes occurring inside the eye.
Between the cornea and the iris there is a space called the anterior chamber. The angle formed by the spherical cornea and the iris is called the anterior angle. This area contains the venous drainage system, which ensures the outflow of excess intraocular fluid. Directly adjacent to the iris at the back is the lens, and then the . The lens is a biconvex lens suspended by many ligaments that are attached to the processes of the ciliary body.
Behind the iris and in front of the lens is the posterior chamber of the eye. Both chambers are filled with intraocular fluid (aqueous humor), which circulates and is renewed in continuous mode. Due to this, nutrients and oxygen are delivered to the lens, cornea and some other structures.
In the very center of the eyeball is the vitreous humor, which is filled with a transparent jelly-like substance and occupies most of the eye. Its main function is to maintain internal tone; it also refracts rays.
The function of the eye is optical. In this system there are several important structures: lens, cornea and retina. It is these three components that are mainly responsible for the transmission of external information.
The cornea has the greatest refractive power. It transmits rays, which then pass through the pupil, which acts as a diaphragm. The main function of the pupil is to regulate the amount of light rays that enter the eye. This indicator is determined by the focal length and allows you to get a clear image with a sufficient degree of illumination.
The lens also has refractive and transmitting powers. It is responsible for focusing rays on the retina, which plays the role of photographic film or matrix.
The intraocular fluid and vitreous body have a small refractive power, but sufficient transmittance. If opacities or additional inclusions are detected in their structure, the quality of vision drops significantly.
After the light passes through all the transparent structures of the eye, a clear inverted image in a reduced version should form on the retina.
The final transformation of external information occurs in the central structures of the brain (occipital cortex).
The structure of the eye is very complex, and therefore a violation of at least one structural link disables the finest optical system and negatively affects the quality of life.
Topic: Structure and functions of the eye.
Visual perception begins with the projection of an image onto the retina and stimulation of photoreceptors, which transform light energy into nervous stimulation. The complexity of visual signals coming from the outside world and the need for their active perception led to the formation in the evolution of a complex optical device. This peripheral device - the peripheral organ of vision - is the eye.
The eye shape is spherical. In adults, its diameter is about 24 mm, in newborns - about 16 mm. The shape of the eyeball in newborns is more spherical than in adults. As a result of this shape of the eyeball, newborn children have farsighted refraction in 80-94% of cases.
Growth of the eyeball continues after birth. It grows most intensively in the first five years of life, less intensively until 9-12 years.
The eyeball consists of three membranes - outer, middle and inner (Fig. 1).
The outer layer of the eye is sclera, or tunica albuginea. This is a dense, opaque white fabric, about 1 mm thick. In the front part it becomes transparent cornea. The sclera in children is thinner and has increased extensibility and elasticity.
The cornea of newborns is thicker and more convex. By the age of 5, the thickness of the cornea decreases, and its radius of curvature remains almost unchanged with age. With age, the cornea becomes denser and its refractive power decreases. Located under the sclera vascular shell of the eye. Its thickness is 0.2-0.4 mm. It contains large number blood vessels. IN anterior section eyeball choroid passes into the ciliary (ciliary) body and iris(iris).
Rice. 1. Diagram of the structure of the eye
The ciliary body contains a muscle connected to the lens and regulating its curvature.
Lens is a transparent elastic formation shaped like a biconvex lens. The lens is covered with a transparent bag; along its entire edge, thin but very elastic fibers stretch towards the ciliary body. They are strongly stretched and keep the lens stretched. The lens in newborns and preschool children is more convex, transparent and more elastic.
There is a round hole in the center of the iris - pupil. The size of the pupil changes, causing more or less light to enter the eye. The lumen of the pupil is regulated by a muscle located in the iris. The pupil of newborns is narrow. At the age of 6-8 years, the pupils are wide due to the predominance of the tone of the sympathetic nerves innervating the muscles of the iris. At 8-10 years of age, the pupil becomes narrow again and reacts very quickly to light. By the age of 12-13 years, the speed and intensity of the pupillary reaction to light is the same as in an adult.
The tissue of the iris contains a special coloring substance - melanin. Depending on the amount of this pigment, the color of the iris ranges from gray and blue to brown, almost black. The color of the iris determines the color of the eyes. In the absence of pigment (people with such eyes are called albinos), light rays enter the eye not only through the pupil, but also through the tissue of the iris. Albinos have reddish eyes. In them, a lack of pigment in the iris is often combined with insufficient pigmentation of the skin and hair. Such people have reduced vision.
Between the cornea and the iris, as well as between the iris and the lens, there are small spaces called the anterior and posterior chambers of the eye, respectively. They contain clear liquid. She supplies nutrients cornea and lens, which are deprived blood vessels. The cavity of the eye behind the lens is filled with a transparent jelly-like mass - the vitreous body.
The inner surface of the eye is lined with a furnace (0.2-0.3 mm), a shell of very complex structure - retina, or retina. It contains light-sensitive cells, named because of their shape cones And with chopsticks. Nerve fibers coming from these cells come together to form the optic nerve, which travels to the brain. In newborns, the rods in the retina are differentiated, the number of cones in the macula (the central part of the retina) begins to increase after birth, and by the end of the first half of the year the morphological development of the central part of the retina ends.
The auxiliary parts of the eyeball include muscles, eyebrows, eyelids, and lacrimal apparatus. The eyeball is moved by four rectus (superior, inferior, medial and lateral) and two oblique (superior and inferior) muscles (Fig. 1).
The medial rectus muscle (abductor) turns the eye outward, the lateral rectus muscle turns the eye inward, the superior rectus moves upward and inward, the superior oblique moves downward and outward, and the inferior oblique moves upward and outward. Eye movements are ensured by the innervation (excitation) of these muscles by the oculomotor, trochlear and abducens nerves.
Eyebrows are designed to protect the eyes from drops of sweat or rain running down from the forehead. The eyelids are movable flaps that cover the front of the eyes and protect them from external influences. The skin of the eyelids is thin, underneath it there is loose subcutaneous tissue, as well as the orbicularis oculi muscle, which ensures the closure of the eyelids during sleep, blinking, and closing the eyes. In the thickness of the eyelids there is a connective tissue plate - cartilage, which gives them shape. Eyelashes grow along the edges of the eyelids. Sebaceous glands are located in the eyelids, thanks to the secretion of which the conjunctival sac is sealed when the eyes are closed. (The conjunctiva is a thin connective membrane that lines the back surface of the eyelids and the front surface of the eyeball to the cornea. When the eyelids are closed, the conjunctiva forms the conjunctival sac). This prevents eye clogging and drying out of the cornea during sleep.
The tear is formed in the lacrimal gland, located in the upper outer corner of the orbit. From the excretory ducts of the gland, tears enter the conjunctival sac, protect, nourish, and moisturize the cornea and conjunctiva. Then by tear ducts it enters the nasal cavity through the nasolacrimal duct. With constant blinking of the eyelids, tears are distributed across the cornea, which maintains its moisture and washes away small foreign bodies. The secretion of the lacrimal glands also acts as a disinfectant liquid.
Nerve visual analyzer :
The optic nerve (n. opticus) is the second parv of the cranial nerves. It is formed by the axons of neurons of the ganglion layer of the retina, which, through the cribriform plate of the sclera, exit the eyeball through a single trunk of the optic nerve into the cranial cavity. At the base of the brain in the area of the sella turcica, the fibers of the optic nerves converge on both sides, forming the optic chiasm and optic tracts. The latter continue to the external geniculate body and the thalamic cushion, then the central visual pathway goes to the cerebral cortex (occipital lobe). Incomplete decussation of the fibers of the optic nerves causes the presence in the right optic tract of fibers from the right halves, and in the left optic tract - from the left halves of the retinas of both eyes.
When the conduction of the optic nerve is completely interrupted, blindness occurs on the side of the damage with the loss of the direct reaction of the pupil to light. When only part of the optic nerve fibers are damaged, focal loss of the visual field (scotomy) occurs. At complete destruction Bilateral blindness develops from the chiasm. However, in many intracranial processes, damage to the chiasm can be partial - loss of the outer or inner halves of the visual fields develops (heteronymous hemianopsia). With unilateral damage to the optic tracts and overlying visual pathways unilateral loss of visual fields on the opposite side occurs. Damage to the optic nerve can be inflammatory, congestive and dystrophic in nature; detected by ophthalmoscopy. The causes of optic neuritis can be meningitis, encephalitis, arachnoiditis, multiple sclerosis, influenza, inflammation of the paranasal sinuses, etc. They are manifested by a decrease in acuity and a narrowing of the visual field, which is not corrected by the use of glasses. A congested optic nerve papilla is a symptom of increased intracranial pressure or impaired venous outflow from the orbit. As congestion progresses, visual acuity decreases and blindness may occur. Optic nerve atrophy can be primary (with tabes dorsalis, multiple sclerosis, optic nerve injury) or secondary (as a result of neuritis or congestive nipple); There is a sharp decrease in visual acuity up to complete blindness, narrowing of the field of view.
III pair of cranial nerves - oculomotor nerve. (n. oculomotorius). Innervates the external muscles of the eye (with the exception of the external rectus and superior oblique), the levator muscle upper eyelid, the muscle that constricts the pupil, the ciliary muscle, which regulates the configuration of the lens, allowing the eye to adjust for near and far vision. System III pair consists of two neurons. The central one is represented by the cells of the cortex of the precentral gyrus, the axons of which, as part of the corticonuclear tract, approach the nuclei of the oculomotor nerve on both its own and the opposite side.
A wide variety of functions performed by the third pair is carried out using 5 nuclei for the innervation of the right and left eyes. They are located in the cerebral peduncles at the level of the superior colliculus of the midbrain roof and are peripheral neurons of the oculomotor nerve. From the two magnocellular nuclei, the fibers go to the external muscles of the eye on their own and partially the opposite side. The fibers innervating the muscle that lifts the upper eyelid come from the nucleus of the same and opposite side. From two small-celled accessory nuclei, parasympathetic fibers are directed to the constrictor pupillary muscle on its own and the opposite side. This ensures a friendly reaction of the pupils to light, as well as a reaction to convergence: constriction of the pupil while simultaneously contracting the rectus intrinsic muscles of both eyes. From the posterior central unpaired nucleus, which is also parasympathetic, the fibers are directed to the ciliary muscle, which regulates the degree of convexity of the lens. When looking at objects located near the eye, the convexity of the lens increases and at the same time the pupil narrows, which ensures a clear image on the retina. If accommodation is impaired, a person loses the ability to see clear outlines of objects at different distances from the eye.
The fibers of the peripheral motor neuron of the oculomotor nerve begin from the cells of the above nuclei and emerge from the cerebral peduncles on their medial surface, then pierce the dura mater and then follow in the outer wall of the cavernous sinus. The oculomotor nerve exits the skull through the superior orbital fissure and goes into orbit.
Disruption of the innervation of individual external muscles of the eye is caused by damage to one or another part of the magnocellular nucleus; paralysis of all muscles of the eye is associated with damage to the nerve trunk itself. An important clinical sign that helps to distinguish between damage to the nucleus and the nerve itself is the state of innervation of the muscle that lifts the upper eyelid and the internal rectus muscle of the eye. The cells from which the fibers go to the muscle that lifts the upper eyelid are located deeper than the rest of the cells of the nucleus, and the fibers going to this muscle in the nerve itself are located most superficially. The fibers innervating the internal rectus muscle of the eye run in the trunk of the opposite nerve. Therefore, when the trunk of the oculomotor nerve is damaged, the first to be affected are the fibers innervating the muscle that lifts the upper eyelid. Weakness of this muscle or complete paralysis develops, and the patient can either only partially open the eye or not open it at all. With a nuclear lesion, the muscle that lifts the upper eyelid is one of the last to be affected. When the core is hit, “the drama ends with the curtain falling.” In the case of a nuclear lesion, all external muscles on the affected side are affected, with the exception of the internal rectus muscle, which is isolated in isolation on the opposite side. As a result of this, the eyeball on the opposite side will be turned outward due to the external rectus muscle of the eye - divergent strabismus. If only the magnocellular nucleus is affected, the external muscles of the eye are affected - external ophthalmoplegia. Because When the nucleus is damaged, the process is localized in the cerebral peduncle, and often in pathological process the pyramidal tract and fibers of the spinothalamic tract are involved, alternating Weber syndrome occurs, i.e. lesion of the third pair on one side and hemiplegia on the opposite side.
In cases where the trunk of the oculomotor nerve is affected, the picture of external ophthalmoplegia is complemented by symptoms of internal ophthalmoplegia: due to paralysis of the muscle that constricts the pupil, pupil dilation occurs (mydriasis), and its reaction to light and accommodation is impaired. The pupils have different sizes (anisocoria).
When exiting the cerebral peduncle, the oculomotor nerve is located in the interpeduncular space, where it is enveloped in soft meninges, which, when inflamed, are often involved in the pathological process. The muscle that lifts the upper eyelid is one of the first to be affected, and ptosis develops (Sapin, 1998).
Think Tank:
The visual center is the third important component of the visual analyzer. According to I.P. Pavlov, the center is the brain end of the analyzer. The analyzer is a nervous mechanism, the function of which is to decompose the entire complexity of the external and internal world into individual elements, i.e. perform analysis. From the point of view of I.P. Pavlov, the brain center, or the cortical end of the analyzer, does not have strictly defined boundaries, but consists of a nuclear and scattered part. The "nucleus" represents a detailed and precise projection in the cortex of all elements of the peripheral receptor and is necessary for the implementation higher analysis and synthesis. "Scattered elements" are located on the periphery of the core and can be scattered far from it. They carry out simpler and more elementary analysis and synthesis.
When the nuclear part is damaged, scattered elements can, to a certain extent, compensate for the lost function of the nucleus, which has great importance to restore this function in humans.
Currently, the entire cerebral cortex is considered to be continuous
receiving surface. The cortex is a collection of cortical ends of the analyzers. Nerve impulses from external environment the body enters the cortical ends of the analyzers of the external world. The visual analyzer also belongs to the analyzers of the external world.
The nucleus of the visual analyzer is located in the occipital lobe. The visual pathway ends on the inner surface of the occipital lobe. The retina of the eye is projected here, and the visual analyzer of each hemisphere is connected to the retinas of both eyes. When the nucleus of the visual analyzer is damaged, blindness occurs. Higher up is an area where vision is preserved and only visual memory is lost. Even higher is the area, when damaged, one loses orientation in an unusual environment.
Analysis of light sensations:
The retina of the eye contains about 130 million rods - light-sensitive cells and more than 7 million cones - color-sensitive elements. The rods are concentrated mainly at the periphery, and the cones are concentrated in the center of the retina. The central fovea of the retina contains only cones. There are no cones or rods in the area where the optic nerve exits (the blind spot). The outer layer of the retina contains pigment fuscin, which absorbs light and makes the image on the retina clearer.
The light-receiving substance in the rods is a special visual pigment - rhodopsin. It contains the proteins opsin and retinene. Cones contain iodopsin, as well as substances that are selectively sensitive to different colors light spectrum. The submicroscopic structure of these receptors shows that the outer segments of the light and color receptors contain from 400 to 800 thin plates located one above the other. Processes extend from the internal segments and go to the bipolar neurons.
Rice. 2. Scheme of the structure of the retina
A I - the first neuron (light-sensitive cells); // - second neuron (bipolar cells); /// - third neuron (ganglion cells); 1 - layer of pigment cells; 2 - sticks; 3- cones; 4 - external border membrane; 5 - bodies of photosensitive cells forming the outer granular layer; 6 - neurons with axons located perpendicular to the course of the fibers of bipolar cells; 7 - bipolar cell bodies forming the internal granular layer; 8 - ganglion cell bodies; 9 - fibers of efferent neurons; 10 - ganglion cell fibers forming at the exit from the eyeball optic nerve; B - stick; B - cone; 11 - external segment; 12 - internal segment; 13 - core; 14 - fiber.
In the central part of the retina, each cone connects to a bipolar neuron. In the periphery of the retina, several cones connect to one bipolar neuron. Between 150 and 200 rods are connected to each bipolar neuron. Bipolar neurons connect to ganglion cells (Fig. 2), the central processes of which form the optic nerve. Excitation from the retinal cells is transmitted along the optic nerve to the neurons of the lateral geniculate body. The processes of the nerve cells of the geniculate body carry excitation to the visual areas of the cerebral cortex (Fig. 3).
Rice. 3. Diagram of visual pathways on the basal surface of the brain:
1 - upper quarter of the visual field; 2- spot area; 3- lower quarter of the visual field; 4 - retina from the side of the nose; B - retina from the side of the temple; b - optic nerve; 7 - optic chiasm; 8 - ventricle; 9 - optic tract; 10 - oculomotor nerve; 11 - nucleus of the oculomotor nerve; 12 - lateral geniculate body; 13 - medial geniculate body; 14 - superior colliculus; 15 - visual cortex; 16 - calcarine groove; 17 - visual cortex (according to K. Pribram, 1975).
Literature:
Dubovskaya L.A. Eye diseases. – M.: Publishing house. "Medicine", 1986.
Kurepina M.M. and others. Human Anatomy. – M.: VLADOS, 2002.
Gain M.G. Lysenkov N.K. Bushkovich V.I. Human anatomy. 5th edition. – M.: Publishing house. "Medicine", 1985.
Sapin M.R., Bilich G.L. Human anatomy. – M., 1989.
Fomin N.A. Human physiology. – M.: Education, 1982
Vision is the channel through which a person receives approximately 70% of all data about the world that surrounds him. And this is possible only for the reason that human vision is one of the most complex and amazing visual systems on our planet. If there were no vision, we would all most likely simply live in the dark.
The human eye has a perfect structure and provides vision not only in color, but also in three dimensions and with the highest sharpness. It has the ability to instantly change focus to a variety of distances, regulate the volume of incoming light, distinguish between a huge number of colors and an even greater number of shades, correct spherical and chromatic aberrations, etc. The eye brain is connected to six levels of the retina, in which the data goes through a compression stage before information is sent to the brain.
But how does our vision work? How do we transform color reflected from objects into an image by enhancing color? If you think about this seriously, you can conclude that the structure of the human visual system is “thought out” to the smallest detail by the Nature that created it. If you prefer to believe that the Creator or some Higher Power is responsible for the creation of man, then you can attribute this credit to them. But let's not understand, but continue talking about the structure of vision.
The structure of the eye and its physiology can frankly be called truly ideal. Think for yourself: both eyes are located in the bony sockets of the skull, which protect them from all kinds of damage, but they protrude from them in such a way as to ensure the widest possible horizontal vision.
The distance the eyes are from each other provides spatial depth. And the eyeballs themselves, as is known for certain, have a spherical shape, due to which they are able to rotate in four directions: left, right, up and down. But each of us takes all this for granted - few people imagine what would happen if our eyes were square or triangular or their movement was chaotic - this would make vision limited, chaotic and ineffective.
So, the structure of the eye is extremely complex, but this is precisely what makes the work of about four dozen of its different components possible. And even if at least one of these elements were missing, the process of vision would cease to be carried out as it should be carried out.
To see how complex the eye is, we invite you to pay attention to the figure below.
Let's talk about how the process of visual perception is implemented in practice, what elements of the visual system are involved in this, and what each of them is responsible for.
As light approaches the eye, light rays collide with the cornea (otherwise known as the cornea). The transparency of the cornea allows light to pass through it into the inner surface of the eye. Transparency, by the way, is the most important characteristic of the cornea, and it remains transparent due to the fact that a special protein it contains inhibits the development of blood vessels - a process that occurs in almost every tissue human body. If the cornea were not transparent, the remaining components of the visual system would have no significance.
Among other things, the cornea prevents debris, dust and any chemical elements from entering the internal cavities of the eye. And the curvature of the cornea allows it to refract light and help the lens focus light rays on the retina.
After light has passed through the cornea, it passes through a small hole located in the middle of the iris. The iris is a round diaphragm that is located in front of the lens just behind the cornea. The iris is also the element that gives the eye color, and the color depends on the predominant pigment in the iris. The central hole in the iris is the pupil familiar to each of us. The size of this hole can be changed to control the amount of light entering the eye.
The size of the pupil will be changed directly by the iris, and this is due to its unique structure, because it consists of two various types muscle tissue (even there are muscles here!). The first muscle is a circular compressor - it is located in the iris in a circular manner. When the light is bright, it contracts, as a result of which the pupil contracts, as if being pulled inward by a muscle. The second muscle is an extension muscle - it is located radially, i.e. along the radius of the iris, which can be compared to the spokes of a wheel. In dark lighting, this second muscle contracts, and the iris opens the pupil.
Many still experience some difficulties when they try to explain how the formation of the above-mentioned elements of the human visual system occurs, because in any other intermediate form, i.e. on any evolutionary stage they simply would not be able to work, but man sees from the very beginning of his existence. Mystery…
Bypassing the above stages, light begins to pass through the lens located behind the iris. The lens is an optical element shaped like a convex oblong ball. The lens is absolutely smooth and transparent, there are no blood vessels in it, and it itself is located in an elastic sac.
Passing through the lens, light is refracted, after which it is focused on the fovea of the retina - the most sensitive place containing the maximum number of photoreceptors.
It is important to note that the unique structure and composition provide the cornea and lens with a high refractive power, guaranteeing a short focal length. And how surprising it is that such complex system fits in just one eyeball (just think what a person could look like if, for example, a meter was required to focus light rays coming from objects!).
No less interesting is that the combined refractive power of these two elements (cornea and lens) is in excellent correlation with the eyeball, and this can be safely called another proof that visual system created simply unsurpassed, because the process of focusing is too complex to talk about it as something that happened only through step-by-step mutations - evolutionary stages.
If we are talking about objects located close to the eye (as a rule, a distance of less than 6 meters is considered close), then everything is even more curious, because in this situation the refraction of light rays turns out to be even stronger. This is ensured by an increase in the curvature of the lens. The lens is connected via ciliary bands to ciliary muscle, which, when contracting, allows the lens to take on a more convex shape, thereby increasing its refractive power.
And here again we cannot fail to mention the complex structure of the lens: it consists of many threads, which consist of cells connected to each other, and thin belts connect it with the ciliary body. Focusing is carried out under the control of the brain extremely quickly and completely “automatically” - it is impossible for a person to carry out such a process consciously.
The result of focusing is the concentration of the image on the retina, which is multilayer fabric, sensitive to light, covering the back of the eyeball. The retina contains approximately 137,000,000 photoreceptors (for comparison, modern digital cameras, in which there are no more than 10,000,000 similar sensory elements). Such a huge number of photoreceptors is due to the fact that they are located extremely densely - approximately 400,000 per 1 mm².
It would not be out of place here to cite the words of microbiologist Alan L. Gillen, who speaks in his book “The Body by Design” about the retina of the eye as a masterpiece of engineering design. He believes that the retina is the most amazing element of the eye, comparable to photographic film. Photosensitive retina, located on the back of the eyeball, is much thinner than cellophane (its thickness is no more than 0.2 mm) and much more sensitive than any human-made photographic film. The cells of this unique layer are capable of processing up to 10 billion photons, while the most sensitive camera can process only a few thousand. But what’s even more surprising is that human eye can capture single photons even in the dark.
In total, the retina consists of 10 layers of photoreceptor cells, 6 layers of which are layers of light-sensitive cells. 2 types of photoreceptors have a special shape, which is why they are called cones and rods. Rods are extremely sensitive to light and provide the eye with black-and-white perception and night vision. Cones, in turn, are not so sensitive to light, but are able to distinguish colors - optimal performance of cones is noted in daytime days.
Thanks to the work of photoreceptors, light rays are transformed into complexes of electrical impulses and sent to the brain at incredibly high speed, and these impulses themselves travel over a million nerve fibers in a fraction of a second.
The communication of photoreceptor cells in the retina is very complex. Cones and rods are not directly connected to the brain. Having received the signal, they redirect it to bipolar cells, and they redirect the signals they have already processed to ganglion cells, more than a million axons (neurites along which nerve impulses are transmitted) which form a single optic nerve, through which data enters the brain.
Two layers of interneurons, before visual data is sent to the brain, facilitate parallel processing of this information by six layers of perception located in the retina. This is necessary so that images are recognized as quickly as possible.
After the processed visual information enters the brain, it begins to sort, process and analyze it, and also forms a complete image from individual data. Of course, about work human brain There is still a lot that is unknown, but even what the scientific world can provide today is enough to be amazed.
With the help of two eyes, two “pictures” of the world that surrounds a person are formed - one for each retina. Both “pictures” are transmitted to the brain, and in reality the person sees two images at the same time. But how?
But the point is this: the retinal point of one eye exactly corresponds to the retinal point of the other, and this suggests that both images, entering the brain, can be superimposed on each other and combined together to obtain a single image. The information received by the photoreceptors in each eye converges in the visual cortex, where a single image appears.
Due to the fact that the two eyes may have different projections, some inconsistencies may be observed, but the brain compares and connects the images in such a way that a person does not perceive any inconsistencies. Moreover, these inconsistencies can be used to obtain a sense of spatial depth.
As you know, due to the refraction of light, visual images entering the brain are initially very small and upside down, but “at the output” we get the image that we are used to seeing.
In addition, in the retina, the image is divided by the brain in two vertically - through a line that passes through the retinal fossa. The left parts of the images received by both eyes are redirected to , and the right parts are redirected to the left. Thus, each of the hemispheres of the viewing person receives data from only one part of what he sees. And again - “at the output” we get a solid image without any traces of connection.
The separation of images and extremely complex optical pathways make it so that the brain sees separately from each of its hemispheres using each of the eyes. This allows you to speed up the processing of the flow of incoming information, and also provides vision with one eye if suddenly a person for some reason stops seeing with the other.
We can conclude that the brain, in the process of processing visual information, removes “blind” spots, distortions due to micro-movements of the eyes, blinks, angle of view, etc., offering its owner an adequate holistic image of what is being observed.
Another one of important elements the visual system is . There is no way to downplay the importance of this issue, because... In order to be able to use vision properly at all, we must be able to turn our eyes, raise them, lower them, in short, move our eyes.
In total, there are 6 external muscles that connect to the outer surface of the eyeball. These muscles include 4 rectus muscles (inferior, superior, lateral and middle) and 2 obliques (inferior and superior).
At the moment when any of the muscles contracts, the muscle that is opposite to it relaxes - this ensures smooth eye movement (otherwise all eye movements would be jerky).
When you turn both eyes, the movement of all 12 muscles (6 muscles in each eye) automatically changes. And it is noteworthy that this process is continuous and very well coordinated.
According to the famous ophthalmologist Peter Janey, control and coordination of the communication of organs and tissues with the central nervous system through nerves (this is called innervation) of all 12 eye muscles is one of the very complex processes occurring in the brain. If we add to this the accuracy of gaze redirection, the smoothness and evenness of movements, the speed with which the eye can rotate (and it amounts to a total of up to 700° per second), and combine all this, we will actually get a mobile eye that is phenomenal in terms of performance. system. And the fact that a person has two eyes makes it even more complex - with synchronous eye movements, the same muscular innervation is necessary.
The muscles that rotate the eyes are different from the skeletal muscles because... they are made up of many different fibers, and they are also controlled a large number neurons, otherwise precision of movements would become impossible. These muscles can also be called unique because they are able to contract quickly and practically never get tired.
Considering that the eye is one of the most important organs human body, he needs continuous care. It is precisely for this purpose that an “integrated cleaning system,” so to speak, is provided, which consists of eyebrows, eyelids, eyelashes and tear glands.
The lacrimal glands regularly produce a sticky fluid that moves slowly down the outer surface of the eyeball. This liquid washes away various debris (dust, etc.) from the cornea, after which it enters the internal tear duct and then flows down the nasal canal, being eliminated from the body.
Tears contain very powerful antibacterial substance, destroying viruses and bacteria. The eyelids act as windshield wipers - they clean and moisturize the eyes through involuntary blinking at intervals of 10-15 seconds. Along with the eyelids, eyelashes also work, preventing any debris, dirt, germs, etc. from entering the eye.
If the eyelids did not fulfill their function, a person's eyes would gradually dry out and become covered with scars. If there were no tear ducts, the eyes would constantly be filled with tear fluid. If a person did not blink, debris would get into his eyes and he could even go blind. The entire “cleaning system” must include the work of all elements without exception, otherwise it would simply cease to function.
A person’s eyes are capable of transmitting a lot of information during his interaction with other people and the world around him. The eyes can radiate love, burn with anger, reflect joy, fear or anxiety, or fatigue. The eyes show where a person is looking, whether he is interested in something or not.
For example, when people roll their eyes while talking to someone, this can be interpreted very differently from a normal upward gaze. Big eyes children cause delight and tenderness among those around them. And the state of the pupils reflects the state of consciousness in which a person is at a given moment in time. Eyes are an indicator of life and death, if we speak in a global sense. This is probably why they are called the “mirror” of the soul.
In this lesson we looked at the structure of the human visual system. Naturally, we missed a lot of details (this topic itself is very voluminous and it is problematic to fit it into the framework of one lesson), but we still tried to convey the material so that you have a clear idea of HOW a person sees.
You couldn't help but notice that both the complexity and capabilities of the eye allow this organ to surpass even the most modern technologies And scientific developments. The eye is a clear demonstration of the complexity of engineering in a huge number nuances.
But knowing about the structure of vision is, of course, good and useful, but the most important thing is to know how vision can be restored. The fact is that a person’s lifestyle, the conditions in which he lives, and some other factors (stress, genetics, bad habits, diseases and much more) - all this often contributes to the fact that vision can deteriorate over the years, i.e. the visual system begins to malfunction.
But deterioration of vision in most cases is not an irreversible process - knowing certain techniques, this process can be reversed, and vision can be made, if not the same as that of a baby (although this is sometimes possible), then as good as possible for each individual person. Therefore, the next lesson in our course on vision development will be devoted to methods of vision restoration.
Look at the root!
If you want to test your knowledge on a topic this lesson, you can take a short test consisting of several questions. For each question, only 1 option can be correct. After you select one of the options, the system automatically proceeds to next question. The points you receive are affected by the correctness of your answers and the time spent on completion. Please note that the questions are different each time and the options are mixed.
An intricate diagram, reminiscent of a camera, depicts the structure of the human eye. It is represented by a spherical paired organ of vision, with the help of which the brain receives a lot of information about environment. The human eye is made up of three layers: outer shell eyes - sclera and cornea, middle - choroid and lens and inner - retina. Anatomy of the skull, where is it located visual organ a person, reliably protects him from external damage, but its structure is very vulnerable to mechanical, physical and chemical influences.
The structural diagram has the most complex structure after the brain. The tunica albuginea is represented by the sclera, which forms a spherical shape. It consists of white fibrous tissue. This is the outer layer. The sclera connects to the muscles that allow the movement of the eyeballs. In front of the sclera is the cornea, and behind is the passage of the optic nerve.
The anatomy of the middle layer is represented by the choroid, which includes the vessels located at the back of the eyes, the iris and the ciliary body, consisting of many tiny fibers that form the ciliary band. Its main function is to support the lens. At the center of the iris is the pupil. Its size changes due to the work of the muscles surrounding the lens. Depending on the lighting, the pupil can expand or contract. Inner shell forms the retina, consisting of photoreceptors - rods and cones.
The table characterizes the structure and functions of the eye with a description of the most important structural functions, which activate all the vision devices, without which a person could not see normally:
| Components of the eye | Functions | Shell |
| Cornea | Refracts light rays, a component of the optical system | Outdoor |
| Sclera | White membrane of the eye | |
| Protection against exposure to excessive light, injury and damage | ||
| Maintaining intraocular pressure | ||
| Iris | Determines the color of a person's eyes | Vascular |
| Luminous flux regulation | ||
| Protecting light-sensitive cells | ||
| Ciliary body | Production of intraocular fluid | |
| Contains muscle fibers that change the shape of the lens | ||
| Choroid | Retinal nutrition | |
| Pupil | Changes size depending on light level | Center of the iris |
| Provides the ability to see far and near. | ||
| Retina | Displaying Visible Objects | Internal |
| Consists of rod and cone photoreceptors | ||
| Lens | Refraction of light rays | |
| Focusing on a subject | ||
| Vitreous body | Transparent gel-like mass | |
| Separation of the lens from the fundus of the eye | ||
| Eyelids | Damage protection partition | Around the eyeball |
| Divided into upper and lower | ||
| During closure, the eye is washed with tear fluid and the surface is mechanically cleaned of trapped particles of dust and dirt. |
The structure of the human eye differs from all biological representatives of the Earth in the existing whites of the eyes.
Eye system. The human vision system is designed to refract and focus light. At the same time, in the back ocular area the smallest light image of a visible object appears, which is then transmitted to the brain as nerve impulses. The visual process has a strict sequence. After light enters the eyes, it passes through the cornea. As light rays are refracted, they move closer to each other. Next control element visual description- lens. With its help, light rays are fixed behind the retina, where the photosensitive sticks and cones, they transmit electrical current to the brain along the optic nerve.
Recognition and construction of information occurs in the visual cortex, located in the occipital part of the brain. The information received from the right and left eyes is mixed to form a single picture. All images received by the retina are inverted and are further corrected by the brain.
More than 80% of all information that we receive from the surrounding reality comes through the channels of visual perception: in other words, we mainly see this world. The other senses make a much smaller contribution to the matter of knowledge, and only after losing sight can a person be surprised to discover what rich potential he has.
We are so used to looking and seeing that we don’t even think about how this happens. Let's be curious and discover that the mechanisms of vision are very similar to photography techniques, and the structure and functions of the eye are one in the same as an ordinary camera.
The human organ of vision is shaped like a small ball. Let's start studying it anatomy outside and we will move towards the center:
A cross-sectional diagram of the structure of the human eye is shown in the figure. Here you can see the designations of the main structures of the eye:
The eye is an extremely fragile and terribly important organ, so it needs to be abundantly nourished and reliably protected. Nutrition is provided by a wide capillary network, protection is provided by all surrounding structures:
Eyes are unusually businesslike organs. They move, turn, and shrink all the time. To do all this, you need a powerful muscular apparatus, represented by six external oculomotor muscles:
The internal structure of a person is the result of the work of the most skilled craftsman in the world - nature. Some mechanisms and systems of the body amaze the imagination with their complexity and filigree precision. But the eye works quite simple, people have been able to do something similar since ancient times:
A schematic description of the visual process is presented in the picture:
Parallel rays of light enter the eye through the pupil and are collected by the lens. Normally, they focus directly on the surface of the retina. In this case, the image turns out clear, and we can talk about good vision. But this only happens if the distance from the lens to the retina is exactly equal to the focal length of the lens.
But not all eyes are equally round. It happens that the body of the organ is elongated and looks like a cucumber. In this case, the rays collected by the lens do not reach the retina and are focused somewhere in vitreous body. Because of this, a person sees poorly distant objects appear blurry. This condition is called myopia, or, scientifically, myopia.
It also happens the other way around. If the eye is slightly flattened from front to back, the focus of the lens is behind the retina. This makes it difficult to clearly distinguish close objects and is called farsightedness (hyperopia).
At various pathologies The lens, cornea and other structures of the eye may change their shape, which entails errors in the operation of the optical system. Due to incorrect construction of the light path, the rays are focused in the wrong place and in the wrong way. It is very difficult to compensate and treat such defects. In medicine, they are combined under the general term astigmatism.
Violations visual function- the problem is quite common. It can be diagnosed in both adults and children. How formerly pathology detected, the greater the chances of success in the fight against it.
In order for the visual organs to be in order and work like a good camera, it is important to provide them with comfortable living conditions: plentiful food in the form of a rich useful substances blood and high-quality communication in the form of a wide network of neurons. Very important:
Human eyes - powerful and incredibly accurate arranged system. Her good job is of great importance for full life full of impressions and pleasures.
Attention, TODAY only!
