Our body interacts with the environment through the senses, or analyzers. With their help, a person is not only able to “feel” the outside world, on the basis of these sensations he has special forms of reflection - self-awareness, creativity, the ability to anticipate events, etc.
What is an analyzer?
According to IP Pavlov, each analyzer (and even the organ of vision) is nothing but a complex “mechanism”. He is able not only to perceive environmental signals and convert their energy into momentum, but also to perform higher analysis and synthesis.
The organ of vision, like any other analyzer, consists of 3 integral parts:
- the peripheral part, which is responsible for the perception of the energy of external stimulation and its processing into a nerve impulse;
- pathways through which the nerve impulse passes directly to the nerve center;
- the cortical end of the analyzer (or the sensory center) located directly in the brain.
All nerve impulses from the analyzers go directly to the central nervous system, where all information is processed. As a result of all these actions, perception arises - the ability to hear, see, touch, etc.
As a sensory organ, vision is especially important, because without a vivid picture life becomes boring and uninteresting. It provides 90% of the information from the environment.
The eye is an organ of vision that has not yet been fully studied, but nevertheless there is an idea of it in anatomy. And this is what will be discussed in the article.
Anatomy and physiology of the organ of vision
Let's look at everything in order.
The organ of vision is the eyeball with the optic nerve and some auxiliary organs. The eyeball has a spherical shape, usually large in size (its size in an adult is ~ 7.5 cubic cm). It has two poles: rear and front. It consists of a nucleus, which is formed by three membranes: the fibrous membrane, the vascular and the retina (or inner membrane). This is the anatomy of the organ of vision. Now about each part in more detail.
Fibrous membrane of the eye
The outer shell of the nucleus consists of the sclera, posterior region, dense connective tissue membrane and cornea, a transparent convex part of the eye, devoid of blood vessels. The cornea is about 1 mm in thickness and about 12 mm in diameter.
Below is a diagram showing a sectional organ of vision. There, you can consider in more detail where this or that part of the eyeball is located.
Vascular membrane
The second name for this shell of the nucleus is choroid. It is located directly under the sclera, is saturated with blood vessels and consists of 3 parts: the choroid itself, as well as the iris and ciliary body of the eye.
The choroid is a dense network of arteries and veins intertwined. Between them is a fibrous loose connective tissue, which is rich in large pigment cells.
In front, the choroid smoothly passes into a thickened ciliary body of a ring-shaped form. Its intended purpose is accommodation of the eye. The ciliary body supports, fixes and stretches the lens. It consists of two parts: the inner (ciliary crown) and the outer (ciliary circle).
About 70 ciliary processes about 2 mm long extend from the ciliary circle to the lens. Zinc ligament fibers (ciliary girdle), attached to the lens of the eye, are attached to the processes.
The ciliary girdle consists almost entirely of the ciliary muscle. When it contracts, the lens expands and rounds, after which its bulge (and with it the refractive power) increases, and accommodation occurs.
Due to the fact that ciliary muscle cells atrophy in old age and connective tissue cells appear in their place, accommodation worsens and hyperopia develops. In this case, the organ of vision does poorly with its functions when a person tries to consider something nearby.
Iris
The iris is a round disk with a hole in the center - the pupil. It is located between the lens and the cornea.
Two muscles pass in the vascular layer of the iris. The first forms the constrictor (sphincter) of the pupil; the second, on the contrary, dilates the pupil.
The color of the eye depends on the amount of melanin in the iris. Photos of possible options are attached below.
The less pigment in the iris, the brighter the eye color. The organ of vision performs its functions in the same way, regardless of the color of the iris.
The gray-green color of the eyes also means only a small amount of melanin.
The dark color of the eye, the photo of which is higher, indicates that the level of melanin in the iris is high.
Inner (photosensitive) shell
The retina is completely adjacent to the choroid. It is formed by two leaves: external (pigmented) and internal (photosensitive).
In a ten-layer photosensitive shell, three-neutron radially oriented chains are distinguished, represented by a photoreceptor outer layer, an associative middle and ganglionic inner layers.
Outside, a layer of epithelial pigment cells is attached to the choroid, which are in close contact with the layer of cones and rods. Both of them are nothing but peripheral processes (or axons) of photoreceptor cells (neuron I).
The sticks are made up of inner and outer segments. The latter is formed using dual membrane disks, which are folds of the plasma membrane. Cones differ in size (they are larger) and the nature of the discs.
In the retina, there are three types of cones and only one type of rod. The number of sticks can reach 70 million, or even more, while cones - only 5-7 million.
As already mentioned, there are three types of cones. Each of them perceives a different color: blue, red or yellow.
Sticks are needed to perceive information about the shape of the subject and the illumination of the room.
A thin process departs from each of the photoreceptor cells, which forms a synapse (the place where two neurons come into contact) with another process of bipolar neurons (neuron II). The latter transmit excitement to larger ganglion cells (neuron III). Axons (processes) of these cells form the optic nerve.
Lens
This is a biconvex crystal clear lens with a diameter of 7-10 mm. It has neither nerves nor vessels. Under the influence of the ciliary muscle, the lens is able to change its shape. It is these changes in the shape of the lens that are called accommodation of the eye. When set to distant vision, the lens flattens, and with near vision it enlarges.
Together with the vitreous, the lens forms the light-refracting medium of the eye.
Vitreous body
He filled all the free space between the retina and the lens. It has a jelly-like transparent structure.
The structure of the organ of vision is similar to the principle of the device of the camera. The pupil acts as a diaphragm, narrowing or expanding depending on the lighting. The lens is the vitreous and the crystalline lens. Light rays fall on the retina, but the image then turns upside down.
Thanks to the light-refracting media (thereby the lens and the vitreous), a beam of light hits the yellow spot on the retina, which is the best area of vision. Cones and rods light waves are reached only after they pass the entire thickness of the retina.
Propulsion system
The motor apparatus of the eye is composed of 4 striated rectus muscles (lower, upper, lateral and medial) and 2 oblique (lower and upper). The rectus muscles are responsible for the rotation of the eyeball in the corresponding direction, and the oblique muscles for the rotations around the sagittal axis. The movements of both eyeballs are synchronous only due to the muscles.
Eyelids
Skin folds, the purpose of which is to limit the palpebral fissure and close it when closed, provide protection for the eyeball in front. There are about 75 eyelashes on each eyelid, the purpose of which is to protect the eyeball from getting a foreign object.
About once every 5-10 seconds, a person blinks.
Lacrimal apparatus
Consists of lacrimal glands and lacrimal system. Tears neutralize microorganisms and are able to moisturize the conjunctiva. Without tears of the conjunctiva, the eyes and cornea would simply dry out and the person would become blind.
The lacrimal glands daily produce about a hundred milliliters of tears. An interesting fact: women cry more often than men, because the hormone prolactin (which girls have much more) contributes to the release of tear fluid.
Basically, a tear consists of water containing approximately 0.5% albumin, 1.5% sodium chloride, a little mucus and lysozyme, which has a bactericidal effect. Has a slightly alkaline reaction.
The structure of the human eye: a diagram
Let's take a closer look at the anatomy of the organ of vision with the help of drawings.
The figure above schematically shows parts of the organ of vision in horizontal section. Here:
1 - tendon of the middle rectus muscle;
2 - rear camera;
3 - cornea of the eye;
4 - the pupil;
5 - a crystalline lens;
6 - front camera;
7 - the iris of the eye;
8 - conjunctiva;
9 - tendon of the rectus lateral muscle;
10 - vitreous body;
11 - sclera;
12 - choroid;
13 - the retina;
14 - a yellow spot;
15 - optic nerve;
16 - blood vessels of the retina.
This figure shows a schematic structure of the retina. The arrow shows the direction of the light beam. The numbers mark:
1 - sclera;
2 - choroid;
3 - retinal pigment cells;
4 - sticks;
5 - cones;
6 - horizontal cells;
7 - bipolar cells;
8 - amacrine cells;
9 - ganglion cells;
10 - optic nerve fibers.
The figure shows a diagram of the optical axis of the eye:
1 - object;
2 - cornea of the eye;
3 - a pupil;
4 - iris;
5 - a crystalline lens;
6 - the central point;
7 is an image.
What are the functions of an organ?
As already mentioned, human vision transmits almost 90% of information about the world around us. Without it, the world would be of the same type and uninteresting.
The organ of vision is a rather complex and not fully understood analyzer. Even in our time, scientists sometimes have questions about the structure and purpose of this body.
The main functions of the organ of vision are the perception of light, the forms of the surrounding world, the position of objects in space, etc.
Light can cause complex changes in the retina and, therefore, is an adequate stimulus for the organs of vision. It is believed that the first to perceive the irritation of rhodopsin.
The highest quality visual perception will be provided that the image of the object will fall on the area of the retinal spot, preferably on its central fossa. The farther from the center the projection of the image of the object, the less distinct it is. Such is the physiology of the organ of vision.
Diseases of the organ of vision
Let's look at some of the most common diseases of the organs of vision.
- Farsightedness. The second name of this disease is hyperopia. A person with this disease does not see objects that are close. Usually difficult to read, work with small objects. It usually develops in people aged, but can also appear in young people. Farsightedness can be completely cured only with the help of operational intervention.
- Myopia (it is also called myopia). The disease is characterized by the inability to clearly see objects that are far enough away.
- Glaucoma is an increase in intraocular pressure. Occurs due to impaired fluid circulation in the eye. It is treated medically, but in some cases surgery may be required.
- Cataracts are nothing more than a violation of the transparency of the lens of the eye. Only an ophthalmologist can help get rid of this disease. Surgical intervention is required in which a person's vision can be restored.
- Inflammatory diseases. These include conjunctivitis, keratitis, blepharitis and others. Each of them is dangerous in its own way and has various methods of treatment: some can be cured with medicines, and some only with the help of operations.
Disease prevention
First of all, you need to remember that your eyes also need to rest, and excessive stress will not lead to anything good.
Use only high-quality lighting with a lamp from 60 to 100 watts.
More often do eye exercises and at least once a year undergo an examination with an ophthalmologist.
Remember that eye diseases are a serious enough threat to the quality of your life.