Vision is one of the ways to know the world around 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 the environment. Due to the ability to see what is around us, we can judge the events that take place, distinguish objects from each other, and also notice threatening factors. The human eyes are designed so 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 - the rods and cones, which are present in the retina of each of us. Thanks to them, the information we perceive about the type of environment is transmitted to the brain.
Eye structure: scheme
Despite the fact that the eye takes up so little space, it contains many anatomical structures, thanks to which we have the ability to see. The organ of vision is almost directly connected to the brain, and with the help of a special study, ophthalmologists see the intersection of the optic nerve. The eyeball has the shape of a ball and is located in a special notch - the orbit that the bones of the skull form. To understand why 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 entities as the vitreous humor, the crystalline lens, the anterior and posterior chambers, the optic nerve and the membranes. Outside, the organ of vision covers the sclera - the protective frame of the eye.
Shell of the eye
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 outside and goes directly to the environment is called the cornea. She possesses 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 shell of the eye - the sclera - consists of a dense connective tissue base. Below it is the next layer - vascular. The middle shell is represented by three formations located in series: the iris,
ciliary (ciliary) body and choreoid. In addition, the vascular layer includes the pupil. It is a small hole not covered with the iris. Each of these entities has its own function, which is necessary to provide 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 shell of the organ of vision.
The structure of the retina
The inner shell of the organ of vision is an integral part of the brain substance. It is represented by layers of neurons that line the eye from the inside. Thanks to the mesh shell, we get an image of everything that is around us. All refracted rays are focused on it and compiled into a clear object. Retinal nerve cells pass into the optic nerve, through the fibers of which information reaches the brain. On the inner lining of the eye there is a small spot that is in the center and has the greatest ability to see. This part is called the macula. In this place there are visual cells - rods and cones of the eye. They provide us with both day and night vision of the world.
The functions of the rods and cones
These cells are located on the
retina of the eye and are necessary in order to see. Sticks and cones are converters of black and white and color vision. Both types of cells act as photosensitive receptors in the eye. 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 conversion of light sensations received from the external environment into electrical signals (pulses) processed by the brain. Specificity to the recognition of daylight belongs to the cones due to the pigment contained in them - iodopsin. This substance has several types of cells that perceive different parts of the spectrum. The sticks are more sensitive to light, so their main function is more complicated - providing visibility at dusk. They also contain a pigment base - the substance rhodopsin, which discolors when exposed to sunlight.
The structure of rods and cones
These cells got their name due to their shape - cylindrical and conical. Rods, unlike cones, are located more on 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 fields of vision. Both types of cells have a similar structure and consist of 4 parts:
- Outer segment - it contains the main pigment of the rod or cone, coated. Rhodopsin and iodopsin are in special containers - disks.
- The cilium is the part of the cell that provides the relationship between the outer and inner segments.
- Mitochondria - they are necessary for energy metabolism. In addition, they contain EPS and enzymes that ensure the synthesis of all cellular components. All this is in the inner segment.
- Nerve endings.
The number of photosensitive receptors on the retina varies greatly. Rod cells make up about 130 million. Retinal cones are significantly inferior to them in quantity, on average there are about 7 million.
Features of the transmission of light pulses
The rods and cones are able to perceive the light flux and transmit it to the central nervous system. Both types of cells are able to work in the daytime. The difference is that the photosensitivity of cones is much higher than that of rods. The transmission of the received signals is carried out thanks to interneurons, to each of which several receptors are attached. The combination of several rod cells at once makes the sensitivity of the organ of vision significantly greater. This phenomenon is called "convergence." It provides us with an overview of several
fields of view at once
, as well as the ability to pick up various movements occurring around us.
Color perception ability
Both types of retinal receptors are necessary not only to distinguish between daytime and twilight vision, but also to determine color images. The structure of the human eye allows a lot: to perceive a large area of the environment, to see at any time of the day. In addition, we have one of the interesting abilities - binocular vision, which allows you to significantly expand the review. Sticks and cones participate in the perception of almost the entire color spectrum, so that people, unlike animals, distinguish all the colors of this world. Color vision to a greater extent is provided by cones, which are of 3 types (short, medium and long-wave). However, the sticks also have the ability to perceive a small part of the spectrum.