What does the human eye consist of? Structure of the eye

Anatomical questions have always been of some interest. After all, they concern each of us directly. Almost all at least once, and interested in what the eye consists of. After all, it is the most sensitive sense organ. It is through the eyes, visually, we get about 90% of the information! Only 9% - with the help of hearing. And 1% - through other bodies. Well, the structure of the eye - this is really an interesting topic, so it is worth considering it as detailed as possible.

Shells

It's worth starting with terminology. The human eye is a paired sensory organ that perceives electromagnetic radiation in the light range of wavelengths.

It consists of shells surrounding the inner core of the organ. Which, in turn, includes watery moisture, the lens and the vitreous. But more on that later.

Telling about what the eye consists of, you need to pay special attention to its shells. There are three. The first is the outer one. Dense, fibrous, the external muscles of the eyeball are attached to it. This shell performs a protective function. And it is she who determines the shape of the eye. Consists of the cornea and sclera.

The middle shell is also called vascular. It is responsible for metabolic processes, provides eye nutrition. It consists of the iris, the ciliary body and the choroid. In the center is the pupil.

And the inner shell is often called mesh. The receptor part of the eye, in which the perception of light and the transmission of information to the central nervous system occur. In general, so you can tell in brief. But, since each component of this body is extremely important, we must separately address each of them with attention. So it will be better to learn what the eye consists of.

Cornea

So, this is the most convex part of the eyeball, making up its outer shell, as well as the light-refracting transparent medium. The cornea looks like a convex-concave lens.

Its main component is the connective tissue stroma. The front cornea is covered with multilayer epithelium. However, scientific words are not very simple in terms of perception, so it's better to explain the topic popularly. The main properties of the cornea are sphericity, specularity, transparency, hypersensitivity and absence of blood vessels.

All of the above causes the "appointment" of this part of the body. In fact, the cornea of the eye is the same as the lens of a digital camera. Even in structure they are similar, because both one and the other is a lens that collects and focuses in the necessary direction light rays. This is the function of the refractive medium.

Telling about what the eye is made of, one can not help but mention the negative effects with which he has to cope. The cornea, for example, is most susceptible to external stimuli. To be more precise - dust, light, wind, mud. As soon as something in the external environment changes, then there is a closing of the eyelids (blinking), photophobia, and tears begin to flow. So, you can say, the protection against damage is activated.

Protection

A couple of words worth mentioning about tears. It is a natural biological fluid. It is produced by the lacrimal gland. A characteristic feature is a slight opalescence. This is an optical phenomenon, due to which light begins to dissipate more intensively, which affects the quality of vision and perception of the surrounding image. The lacrimal liquid is 99% water. One percent is inorganic substances, which are magnesium carbonate, sodium chloride, and calcium phosphate.

Tears have bactericidal properties. They wash the eyeball. And its surface, thus, remains protected from the effects of dust, foreign bodies and wind.

Another component of the eye is the eyelashes. On the upper eyelid, their number is about 150-250. At the bottom - 50-150. And the main function of eyelashes is the same as in tears - protective. They prevent dirt, sand, dust from entering the surface of the eye, and even small insects in the case of animals.

Iris

So, above it was told about what the outer shell of the eye consists of. Now you can tell about the average. Naturally, it will be about the iris. It is a thin and movable diaphragm. It is located behind the cornea and between the chambers of the eye - just in front of the lens. It is interesting that she practically does not let in the light.

Iris consists of pigments that determine its color, and circular muscles (due to which the pupil narrows). By the way, this part of the eye also includes layers. There are only two of them - mesodermal and ectodermal. The first is responsible for the color of the eye, since it contains melanin. In the second layer are pigment cells with fuscin.

If a person has blue eyes, then his ectodermal layer is loose and contains little melanin. This shade is the result of the diffusion of light in the stroma. By the way, the lower its density - the more saturated is the color.

Blue eyes have people with a mutation in the HERC2 gene. They produce a minimum of melanin. The density of the stroma in this case is higher than in the previous case.

In the green eyes, melanin is the most. By the way, the gene of red hair plays an important role in the formation of this shade. Pure green is very rare. But if there is at least a "hint" for this shade, then they are called those.

But most of all melanin is found in brown eyes. They absorb the whole world. As with high, and with low frequencies. And the reflected light gives a brown tinge. By the way, initially, many thousands of years ago, all people were brown-eyed.

There is another black color. The eyes of this shade contain so much melanin that all the light that gets into them is absorbed completely. And, by the way, quite often such "structure" causes a grayish shade of an eyeball.

Vascular membrane

It should also be noted with attention, telling what the human eye consists of. It is located right under the sclera (protein coat). Its main property is accommodation. That is, the ability to adapt to dynamically changing external conditions. In this case it concerns the change in the refractive force. A simple illustrative example of accommodation: if we need to read what is written on the package in small print - we can look at and distinguish words. Need to see something far away? We, too, can do this. In this ability is our ability to clearly perceive objects located at a certain distance.

Naturally, talking about what makes a person's eye, you can not forget about the pupil. This is also quite a "dynamic" part of it. The diameter of the pupil is not fixed, but constantly tapering and widening. This is due to the fact that the flow of light that goes into the eye is regulated. The pupil, changing in size, "cuts off" too bright sunlight on a particularly clear day, and misses the maximum amount in foggy weather or the dark time of the day.

You should know

On such an amazing component of the eye, as the pupil, it is worth pointing. This, perhaps, is the most unusual in the topic under discussion. Why? If only because the answer to the question of what the pupil of the eye is made of is such - from nothing. In fact, it is! After all, the pupil is an opening in the tissues of the eyeball. But next to him are the muscles that allow him to perform the above-named function. That is, to regulate the flow of light.

The unique muscle is the sphincter. It surrounds the extreme part of the iris. It consists of a sphincter of intertwined fibers. Still there is a dilator - the muscle that is responsible for the dilatation of the pupil. It consists of epithelial cells.

It is worth mentioning another interesting fact. The middle shell of the eye consists of several elements, but the pupil is the most fragile. If you believe in medical statistics, then 20% of the population has a pathology called anisocoria. It is a condition in which the pupil sizes are different. They can also be deformed. But not all of these 20% symptom is pronounced. Most do not even know about the presence of anisocoria. Many become aware of it only after a visit to a doctor, to which people are resolved, feeling fogginess, pain, ptosis (omission of the upper eyelid), etc. But some people have diplopia - a "double pupil".

Retina

This is the part that should be noted with special attention, telling about what the human eye consists of. The retina is a thin shell, closely adjacent to the vitreous body. Which, in turn, is the one that fills 2/3 of the eyeball. The vitreous body gives the eye a correct and unchanged shape. And also refracts light coming to the retina.

As already mentioned, the eye consists of three shells. But this is just the basis. After all, another 10 layers consists of the retina of the eye! And to be more precise, its visual part. There is also a "blind", in which there are no photoreceptors. This part is divided into ciliary and iridescent. But it's worth returning to the ten layers. The first five are: pigmented, photosensory and three external (membrane, granular and interwoven). The other layers are similar in name. These are three internal (also granular, interwoven and membranous), and also two, one of which consists of nerve fibers, and the other - of ganglionic cells.

But what exactly is responsible for visual acuity? The parts that make up the eye are interesting, but I want to know the most important thing. So, for the visual acuity is responsible for the central fossa of the retina. It is also called a "yellow spot". It has an oval shape, but is opposite the pupil.

Photoreceptors

An interesting sense organ is our eye. What it consists of - the photo is provided above. But still there was nothing said about photoreceptors. And, to be more precise, about the rods and cones that are on the retina. But this is also an important component.

They contribute to the transformation of light stimulation into information that enters the CNS through the fibers of the optic nerve.

The cones are very sensitive to light. And all because of the content in them iodopsin. It is a pigment that provides color vision. There is still rhodopsin, but this is the complete iodopsin opposite. Because this pigment is responsible for twilight vision.

A person with a good 100-percent vision has about 6-7 million cones. It is interesting that they are less sensitive to light (they are about 100 times worse) than sticks. However, quick movements are better. Rods, incidentally, more - about 120 million. They contain the notorious rhodopsin.

It is the sticks that provide the visual ability of a person in the dark. The cones at night are not active at all - since they need at least a minimum flux of photons (radiation) to work.

Muscles

They also need to be told about them, discussing the parts that make up the eye. Muscles - this is what provides a direct arrangement of apples in the orbit. They all originate from the notorious connective tissue tight ring. The main muscles are called oblique, as they are attached to the eyeball at an angle.

The topic is better explained in plain language. Each movement of the eyeball depends on how the muscles are fixed. We can look to the left without turning our heads. This is due to the fact that the straight motor muscles coincide in their location with the horizontal plane of our eyeball. By the way, they also, in conjunction with the oblique, provide circular turns. Which includes every gym for the eyes. Why? Because all the eye muscles are involved in this exercise. And everyone knows that for this or that training (no matter what it is connected to) has a good effect, it is necessary that every component of the body works.

But this, of course, is not all. There are also longitudinal muscles that start working at the moment when we look into the distance. Often, people whose activities are associated with painstaking or computer work, feel pain in the eyes. And it becomes easier if they are massaged, squeezed, pinched. What causes pain? Because of muscle strain. Some of them work constantly, while others rest. That is, for the same reason that your hands can hurt, if a person carried a heavy thing.

Lenticular

Telling about what parts of the eye consists of, it is impossible not to mention this "element". The lens, which has already been mentioned above, is a transparent body. It is a biological lens, if expressed in simple language. And, accordingly, the most important component of the refractive eye apparatus. By the way, the lens even looks like a lens - it is biconvex, rounded and elastic.

He has a very fragile structure. Outside, the lens is covered with a very thin capsule, which protects it from external factors. Its thickness is only 0.008 mm.

The lens is susceptible to various diseases. The most difficult is cataract. In this disease (age, as a rule) a person sees the world dull, blurry. And in such cases, the replacement of the lens with a new, artificial one is required. Fortunately, he is in our eye in such a place that he can change, without touching the remaining parts.

In general, as can be seen, the structure of our main sense organ is very complex. The eye is small, but includes just a huge number of elements (remember, at least 120 million sticks). And it would be possible to talk about its components for a long time, but the most important ones could be listed.