The structure of the human eye - anatomical features

The human eye is one of the most complex organs of the body because of its special anatomy and physiology. In its structure, it represents an optical system capable of adapting itself to different lighting conditions and any external stimuli. Eyes are the most important analyzer for a person, because with their help we get from 90% of all information about the outside world. They are the primary link in a complex chain of perception, cognition and other mental functions. In the article, we will consider the eye as the organ of vision, its anatomical features and what functions each element.

Structure of the eye

The visual analyzer of a person consists of a peripheral section represented by the eyeball, conductive pathways and cortical structures of the brain.All information arrives on the outside of the eye, and then goes a long way along the nerve arc, reaching the occipital lobe of the cerebral cortex.The process is fully automatic and occurs in just a split second.

Peripheral part

The outer or peripheral part of the visual system is represented by the eyeball. It is located in the eye sockets (orbit), which protect it from damage and injuries. Has the shape of a sphere, up to 7 cm3, the mass of the eyeball is up to 78 grams. In the structure, three membranes are distinguished: fibrous, vascular and retina. Inside the eyeball is a watery liquid - an intraocular fluid that supports the spherical shape and is a light refractive medium.All structural elements are closely related, therefore, in the pathology of any component, all visual processes are inhibited.What diseases are indicated by the violation of peripheral vision read in this article.

Conductive paths

This is a complex physiological system, through which information arriving at the peripheral part of the visual apparatus (mesh envelope) enters the cortical centers of the cerebral hemispheres. After the ray of light reaches deep layers of the retina, a photochemical reaction is triggered.

During this time, energy is transformed into nerve impulses, rushing to the three layers of neurons. Then the pulse through the chain of nerve endings and the visual tract, consisting of the right and left parts, is sent to the subcortical centers of the brain.Regardless of the complexity and volume of information, the signal is transmitted in fractions of a second.

Each hemisphere receives information simultaneously from the left and right eyeball. This physiological aspect underlies the bipolar and three-dimensional view of man.

Subcortical centers

After the information reaches the visual tract, it enters the brain. Nerve endings round the legs of the brain from the outside, and then enter the primary or subcortical centers. The structure of this department includes a pillow of the thalamus, a lateral geniculate body and several nuclei of the upper hills of the midbrain. In them, a bundle of nerves is scattered in a fan-like manner, forming a visual radiance or a beam of Grazioles.This concludes the primary projection of visual information.Further processing takes place in more complex brain structures.

Higher visual centers

The whole surface of the brain is conventionally divided into centers, each of which is responsible for certain functions. To ensure the full functioning of the human body, all areas of the cerebral cortex are closely interrelated. Higher or cortical visual centers are located on the medial surface of the occipital lobe, or rather in the area of ​​the furrow groove. The visual field of the cerebral cortex is number 17. In this conditional zone, several nuclei are allocated, each of which is responsible for certain functions. For example, the core of Yakubovich regulates the functions of the oculomotor nerve.

The visual tract is a complex nerve arc, so when there is at least one element in its composition, complex problems arise.

Experiments on the study of higher visual centers were initially carried out on animals. The opening of the visual center in the brain is attributed to G. Lenz. Subsequently, Soviet and German physiologists actively engaged in this issue.

Eyeball

This is the peripheral part of the visual analyzer. It is in it that the information is received and processed first. Vision develops gradually, therefore in children this organ differs in structure from adults. The eyeball has several membranes, which are suitable for a large number of vessels, nerve endings and muscles. Located in the orbits of turtles, it is protected from the outside by eyelids and eyelashes.

Outside

The fibrous or external part of the eyeball is represented by the cornea and sclera. They radically differ in their functions and anatomical structure, outwardly representing a single dense structure of connective tissue. It has a high elasticity, so it maintains the characteristic spherical shape of the eye.The primary information enters the visual analyzer through the cornea, therefore, with the damage or illnesses, the whole process of vision suffers.

Cornea

This is a transparent shell of the eye, which has a convex shape. Cornea is one of the smallest elements in the eyeball area. Normally, it is a convex-concave lens with a refractive force of 40 dpt. It has a characteristic luster and greater photosensitivity.It is the main refractive medium in the eyes of mammals. There are no blood vessels in its structure, but there are a large number of nerve endings.That is why even the slightest touch to this element leads to seizures of the eyelids, severe pain and intensified blinking. Outside is a pre-corneal film, which is the main defense of the cornea from external influences.

Among the diseases of the cornea, the most common are dystrophy and keratitis - its inflammation.

Sclera

The white membrane or sclera is the most dense element of the eye. It consists of bundles of collagen fibers and dense connective tissue, in the thickness of which the eye muscles are attached. It consists of two main elements - the episcler and the suprachoroidal space. The average thickness of the sclera is -1 mm, and in young children it is still developed so weakly that the visual pigment of blue color shines through it. Performs a supporting and supporting function, thanks to it the tone and shape of the eyeball is preserved. The area where the sclera passes into the cornea is called the limb. This is one of the thinnest places of the outer shell of the eyeball.

Vascular membrane

The uveal tract is the middle structure of the eye, located under the sclera. Has a soft texture, pronounced pigmentation and a large number of blood vessels. It is necessary for nutrition of retinal cells, and also participates in the basic visual processes - accommodation and adaptation. The vascular envelope is represented by three main structures - the iris, ciliary (ciliated) body and choroid. ATthe inflammation of this part of the eyeball is called uveitis, which in 25% of cases is the cause of blindness, vision and fog in front of the eyes.

Iris

Anatomically located behind the cornea of ​​the eyeball, just before the lens. Under the magnification of the microscope, it is possible to detect a spongy structure consisting of a number of thin bridges (trabeculae). In its center there is a pupil - a hole up to 12 mm in size, which can be adjusted to any light stimuli. Performs the function of the aperture, as it expands and contracts, depending on the brightness of the illumination. Its color is formed only by 12 years, can be different, which is determined by the content of melanin in the composition. It is the iris that protects the human eye from the overabundance of sunlight. The absence or deformation of the iris in medicine is called a coloboma.

Ciliary body

The ciliary or ciliary body has the shape of a ring and is located at the base of the iris, connecting with it with a small smooth muscle. It provides the curvature and focus of the lens.It is believed that the ciliated body is the key link in the process of accommodation of the human eye - the ability to maintain seeing objects at different distances.The processes of the ciliary body produce the intraocular fluid, and also carry nutrients to the eye formations, which contain no blood vessels (lens, cornea and vitreous body).

Choroid

Occupies no less than 2/3 of the area of ​​the vascular tract, therefore technically it is the choroid of the eye. The main task of this element is nutrition of all structural elements of the eye. In addition, it takes an active part in the regeneration of cells that decay with age. It is found in all mammalian species and has a characteristic dark brown or black color depending on the concentration of blood vessels and chromatophores. Has a complex structure, which includes more than 5 layers.

Choroiditis is one of the most common diseases of the choroid of the eye in old age. It differs in that it is difficult to treat and leads to a significant inhibition of visual functions.

Retina

The initial structural element of the peripheral part of the visual analyzer. It is a photosensitive shell, the thickness of which can reach, mm. In the structure there are 10 layers of cells having different functions. It is here that the light ray is transformed into a nervous excitement, so the retina is often compared with the film of the camera.Thanks to special light-sensitive cells - cones and rods, it forms the image.They are located on the entire visual side, down to the ciliary body. A place where there are no photosensitive elements is called a blind spot.

In the elderly, retinal dystrophy is often observed, and night blindness develops. This is explained by the age-related depletion of the body and a decrease in the function of cell regeneration.

The human retina contains about 7 million. cones and 125 million. chopsticks, depending on their concentration, various visual ailments may develop, for example, twilight vision.

Cavity of the eye

Inside the eyeball is a light-conducting and light-refracting medium. It is represented by three basic elements - watery moisture in the anterior and posterior chamber, the lens and the vitreous body.

Intraocular fluid

Watery moisture is in the front of the eyeball in the space between the cornea and the iris. The posterior chamber is located between the iris and the lens. Both departments are connected through the pupil.Intraocular fluid constantly moves between chambers, if this process stops, visual functions become weaker.Disturbance of outflow of the eye fluid is called glaucoma and in the absence of treatment leads to blindness. In its composition, it is similar to blood plasma, but due to filtration by the ciliary sprouts practically does not contain protein and other elements.

The eye of an adult man daily produces from 3 to 8 ml of watery moisture.

Intraocular pressure is directly related to watery moisture. Physiologically, this is the ratio of the intraocular fluid formed and discharged into the bloodstream.

Lenticular

It is located directly behind the pupil, between the vitreous body and the iris. It is a biological biconvex lens that, with the help of the ciliated body, can change its curvature, allowing it to focus in objects distant at different distances. The lens is colorless, has an elastic structure.Depending on the tone of the muscle fibers, the refractive power of the lens leaves 20-30 D, and the thickness is within 3-5 mm.A violation of the transparency of the lens leads to the development of cataracts. Feature is that diseases of glaucoma and cataracts are closely related, because in violation of outflows the process of supplying the necessary nutrients that support transparency is lost the lens.

The lens is surrounded by a very thin film, which protects it from dissolution and deformation by water, which is behind it in the vitreous body.

Vitreous body

It is a transparent substance in the form of a gel that fills the space between the lens and the retina of the eye. Normally in an adult, its volume should be at least 2/3 of the entire eyeball (up to 4 ml). On 99% consists of water in which molecules of amino acids and hyaluronic acid are dissolved.Within the vitreous body are hyalocytes - cells that produce collagen.In recent years, active work has been carried out to cultivate them, which makes it possible to create an artificial vitreous body without silicone elements for the procedure of vitrectomy.

Protective apparatus of the eye

The eyeball is protected from all sides by mechanical damages, dirt and dust, which is necessary for its full operation. From the inside, the defense is provided by the eye sockets of the skull, and from the outside - eyelids, conjunctiva and eyelashes. In newborn children, this system is not yet fully developed, so it is at this age that conjunctivitis, an inflammation of the mucous membrane of the eyes, is most often observed.

Glaznitsa

This is a pair of cavities in the skull, which contains the eyeball and its appendages - the nerve and vascular endings, the muscles surrounded by fatty tissue.The ocellus or orbit is a pyramidal cavity facing the interior of the skull. Has four edges, formed by different in form and size bones.Normally, an adult has a volume of 30 ml of orbit, of which only the eyeball falls, all the other space is occupied by various shells and protective elements.

Eyelids

These are the movable folds surrounding the outer part of the eyeball. They are necessary for protection against external influences, uniform moistening with tear fluid and cleaning from dust and dirt. The eyelid consists of two layers, the boundary between which is on the free edge of this structure. It is located meibomian glands. The outer surface is covered with a very thin layer of epithelial tissue, and at the end of the eyelids are eyelashes, which act as a kind of eye brush.

Conjunctiva

A thin transparent shell of epithelial tissue that covers the eyeball from the outside and the posterior surface of the eyelids. Performs an important protective function - produces mucus, due to which the external structures of the eyeball are wetted and lubricated. On the one hand passes to the skin of the eyelids, and on the other hand it ends with the epithelium of the cornea. Inside the conjunctiva are additional tear glands. Its thickness is no more than 1 mm in an adult, the total area is 16 cm2. Visual examination of the conjunctiva can diagnose some diseases. For example, with jaundice, it turns yellow, and when anemia it turns into bright white.

The inflammatory process of this element is called conjunctivitis and is considered the most common eye disease.

The conjunctiva, localized at the nasal corner of the eye, forms a characteristic fold, due to which it is called the third century. In some species of animals, it is so pronounced that it covers most of the eye.

Lacrimal and muscular apparatus

Tears are a physiological fluid that is necessary to protect, nourish and maintain the optical functions of the outer structures of the eyeball. The device consists of a lacrimal gland, dots, tubules, as well as a lacrimal sac and a nasolacrimal duct. The gland is located in the upper part of the orbit.This is where the synthesis of tears occurs, which then passes through the conducting channels to the surface of the eye.Inflammation of the lacrimal sac or tubules in ophthalmology is called dacryocystitis. It flows into the conjunctival vault, after which it is transported through the lacrimal ducts to the nose. A day a healthy person is allocated no more than 1 ml of this liquid.

The mobility of the eye is provided by six oculomotor muscles. Of these, 2 have a slanting shape, and 4 - a straight line. In addition, a full work provides the muscles that raise and lower the eyelid. All fibers are innervated by several eye nerves, so that fast and synchronous operation of the eyeball is achieved.

Nearsightedness or myopia, as a rule, develops precisely because of the overstrain of oblique oculomotor muscles, called spasm of accommodation.

Video

This video is about what the human eye consists of and how the picture is interpreted.

conclusions

1. The human eye is an organ that is complex in structure and physiology, which consists of the eyeball, its membranes, cavity and protective apparatus.
2. Information processing begins in the peripheral part of the visual analyzer, and then enters the higher visual centers located in the occipital lobe of the brain.
3. The outer part of the eye consists of several membranes (fibrous, vascular and reticular), in the structure of which several structural elements are distinguished.
4. The spherical shape of the eyeball is provided by the intraocular fluid and sclera.
5. The orbital (orbits), eyelids, conjunctiva and lacrimal gland perform a protective function.
6. For the movement of the eyeball in space, 6 muscles respond, which are innervated by nerve endings.

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