What is the part of the eye around the pupil called? How the human eye works and why the brain needs Photoshop
Our eye is a complex optical system whose main task is to transmit images. optic nerve.
Initially visible image passes through the cornea. This is where the primary refraction of light occurs. From there, it reaches the lens through a round hole in the iris called the pupil. Since the lens is a biconvex lens, after passing through the vitreous, the visible image when it hits the retina is inverted. It is the signal from the inverted image that travels from the retina along the optic nerve to the brain. And that’s what the brain is for, to flip the image back.
The structure of the human eye cannot be considered separately without two other parts of the visual apparatus - the pathways and the area of the brain (visual cortex), which are responsible for conducting and analyzing nerve impulses coming from the eye: a person looks with the eye, and sees with the brain. In addition, when considering the structure of the human eye, it is necessary to say something about its appendage apparatus. The eyeball forms an integral system with auxiliary structures: oculomotor muscles, eyelids, mucous membrane (conjunctiva) and lacrimal apparatus.
External structure
Here you can highlight the eyelids (upper and lower), eyelashes, the inner corner of the eye with the lacrimal caruncle (fold of the mucous membrane), white part eyeball- the sclera, which is covered with a transparent mucous membrane - the conjunctiva (read more about this formation of the eye in the section Conjunctiva), the transparent part - the cornea, through which the round pupil and iris are visible (individually colored, with a unique pattern). The junction of the sclera and the cornea is called the limbus.
The eyeball has an irregular spherical shape, anterior-posterior size for an adult, it is about 23-24 mm.
The eyes are located in a bony container - the eye sockets. On the outside, they are protected by eyelids; the edges of the eyeballs are surrounded by extraocular muscles and fatty tissue. WITH inside The optic nerve leaves the eye and goes through a special canal into the cranial cavity, reaching the brain.
Eyelids
The eyelids (upper and lower) are covered on the outside with skin, on the inside with mucous membrane (conjunctiva). In the thickness of the eyelids there are cartilages, muscles (the orbicularis oculi muscle and the levator muscle). upper eyelid) and glands. The eyelid glands produce components of the eye's tears, which normally wet the surface of the eye. On the free edge of the eyelids, eyelashes grow, which perform protective function, and the gland ducts open. Between the edges of the eyelids there is a palpebral fissure. Located in the inner corner of the eye, on the upper and lower eyelids lacrimal puncta- holes through which tears flow through the nasolacrimal duct into the nasal cavity.Muscles of the eye
The muscles of the eye, of which there are six on each eyeball: four rectus muscles: internal, external, superior and inferior rectus muscles, and two obliques: superior and inferior. The muscular apparatus of the eye ensures rotation of the eyeball in all directions, as well as coordinated fixation of the gaze of both eyes at a certain point.The lacrimal gland is located in the upper-outer part of the orbit. It produces tear fluid in response to emotional stimulation or irritation of the mucous membrane of the eye, cornea or nasopharynx. You can see the structure of the lacrimal apparatus of the human eye in more detail in the lacrimal apparatus section.
Eye shells
The human eyeball has 3 membranes: outer, middle and inner.
Sclera
The sclera occupies 4/5 of the part fibrous membrane and consists of connective tissue, it is quite dense and they are attached to it eye muscles. The main function is protective; it provides a certain shape and tone of the eyeball. From the posterior pole of the eye there is an exit point in the sclera optic nerve- cribriform plate.Cornea
The cornea makes up 1/5 of the outer shell, it has a number of characteristics: transparency (absence of blood vessels), shine, sphericity and sensitivity. All these signs are characteristic of a healthy cornea. With diseases of the cornea, these signs change (turbidity, loss of sensitivity, etc.). The cornea belongs to the optical system of the eye, it conducts and refracts light (its thickness in different sections ranges from 0.2 to 0.4 mm, and the refractive power of the cornea is approximately 40 diopters). More Full description You will find the structure of the cornea in the corresponding section: Cornea.The middle (choroid) of the eye consists of the iris, ciliary body and the choroid itself (choroid), which are located directly under the sclera. The middle layer of the eye provides nutrition to the eyeball and is involved in metabolic processes and removal of waste products from eye tissue.
Iris
The iris is the anterior part of the vascular tract of the eye, it is located behind the transparent cornea, in the center there is an adjustable round hole - the pupil. Thus, in the structure of the human eye, the iris plays the role of a diaphragm, painted in a certain color. A person's eye color is determined by the amount of melanin pigment in the iris (from light blue to brown). This pigment protects the eyes from excess sunlight. The pupil diameter varies from 2 to 8 mm, depending on the light level, nervous regulation or the effects of medications. Normally, the pupil contracts in bright light and dilates in low light. Ciliary body
The ciliary body is a section of the choroid located at the base of the iris. In the thickness of the ciliary body there is a ciliary muscle, which changes the curvature of the biological lens of the eye - the crystalline lens, thus directing the focus to the desired distance (accommodation of the eye occurs).The choroid itself (choroid) makes up the majority of the vascular tract of the eye (2/3) and serves as nutrition for the inner lining of the eye - the retina.
Lens
The lens is located behind the pupil; it is a biological lens, which, under the influence of the ciliary muscle, changes the curvature and participates in the act of accommodation of the eye (focusing the gaze on objects at different distances). The refractive power of this lens varies from 20 diopters at rest to 30 diopters when the ciliary muscle is working.In addition, in the eyeball one can distinguish the anterior and posterior chambers of the eye - spaces filled with aqueous humor - fluid circulating inside the eye and performing a nutritional function for the cornea and lens (normally, these formations do not have blood vessels). The anterior chamber of the eye is located between the cornea and the iris, the posterior chamber is located between the iris and the lens of the eye. Aqueous humor is produced by the processes of the ciliary body, then flows through the pupil into the anterior chamber, and then through a special drainage system(trabecular apparatus) flows into the vasculature, as shown in the figure:
Behind the lens there is a volumetric formation that fills the eye, the vitreous body, which has a jelly-like consistency. Functions vitreous- light transmission and maintaining the shape of the eyeball.
Retina
The retina (the inner, sensitive layer of the eye) lines the cavity of the eyeball from the nutria. This is the thinnest of the eye membranes, its thickness ranges from 0.07 to 0.5 mm. The retina has complex structure and consists of 10 layers of cells. This shell of the eye can be compared to the film of a camera; its main role is image formation (light and color perception), with the help of special sensitive cells - rods and cones. The rods are located mainly on the periphery of the retina and are responsible for black-and-white, twilight vision. Cones are concentrated in central departments retina - macula, and are responsible for small details of objects and colors. Nerve fibers coming from sensory cells form the optic nerve, which leaves the posterior pole of the eye and penetrates the cranial cavity, into the brain.Lacrimal organs and muscles that move the eyeball). The shape of the eyeball (Fig. 1) has a not entirely regular spherical shape: the anterior-posterior size in an adult is on average 24.3 mm, vertical - 23.4 mm and horizontal - 23.6 mm; the size of the eyeball can be larger or smaller, which is important for the formation of the refractive ability of the eye - its refraction (see Myopia, Farsightedness).
Rice. 1. (section of the eyeball in a horizontal plane; semi-schematic): 1 - cornea; 2 - anterior chamber; 3 - ciliary muscle; 4 - vitreous body; 5 - retina; 6 - the choroid itself; 7 - sclera; 8 - optic nerve; 9 - perforated scleral plate; 10 - jagged line; 11 - ciliary body; 12 - rear camera; 13 - conjunctiva of the eyeball; 14 - iris; 15 - lens.
The walls of the eye consist of three concentrically located membranes - outer, middle and inner. They surround the contents of the eyeball - the lens, vitreous body, intraocular fluid (aqueous humor). The outer shell of the eye is the opaque sclera, or tunica albuginea, occupying 5/6 of its surface; in its anterior section it is connected to the transparent cornea. Together they form the corneal-scleral capsule of the eye, which, being the most dense and elastic outer part eyes, performs a protective function, constituting, as it were, the skeleton of the eye. The sclera is formed from dense connective tissue fibers, its thickness is on average about 1 mm.
The sclera is greatly thinned in the region of the posterior pole of the eye, where it turns into a cribriform plate through which fibers pass that form the optic nerve of the eye. In the anterior part of the sclera, almost at the border of its transition into cornea, a circular sine is laid, the so-called. Schlemm's canal (named after the German anatomist F. Schlemm, who first described it), which is involved in the outflow of intraocular fluid. In front, the sclera is covered with a thin mucous membrane - the conjunctiva, which passes posteriorly to inner surface upper and lower eyelids.
The cornea has an anterior convex and posterior concave surface; its thickness in the center is about 0.6 mm, at the periphery - up to 1 mm. In terms of optical properties, the cornea is the most powerful refractive medium of the eye. It is also like a window through which rays of light pass into the eyes. There are no blood vessels in the cornea; its nutrition is carried out by diffusion from the vascular network located at the border between the cornea and sclera. Thanks to numerous nerve endings located in the superficial layers of the cornea, it is the most sensitive outer part of the body. Even a light touch causes a reflexive instant closing of the eyelids, which prevents foreign bodies from entering the cornea and protects it from cold and heat damage.
Directly behind the cornea is the anterior chamber of the eye - a space filled with clear liquid, the so-called. chamber moisture, which chemical composition close to the cerebrospinal fluid (See. Cerebrospinal fluid). The anterior chamber has a central (average depth of 2.5 mm) and peripheral sections - the angle of the anterior chamber of the eye. This section contains a formation consisting of interwoven fibrous fibers with tiny holes through which chamber moisture is filtered into Schlemm's canal, and from there into the venous plexuses located in the thickness and on the surface of the sclera. Thanks to the outflow of chamber moisture, it is maintained at normal level intraocular pressure. Rear wall the anterior chamber is the iris; in its center there is a pupil - a round hole with a diameter of about 3.5 mm.
The iris has a spongy structure and contains pigment, depending on the amount of which and the thickness of the shell, the color of the eyes can be dark (black, brown) or light (gray, blue). There are also two muscles in the iris that dilate and contract the pupil, which acts as the diaphragm of the optical system of the eyes - in the light it narrows (direct reaction to light), protecting the eyes from strong light irritation, in the dark it expands (reverse reaction to light), allowing capture very weak light rays.
The iris passes into the ciliary body, which consists of a folded anterior part, called the corona of the ciliary body, and a flat posterior part and produces intraocular fluid. In the folded part there are processes to which thin ligaments are attached, which then go to the lens and form its suspensory apparatus. The ciliary body contains an involuntary muscle involved in the accommodation of the eye. The flat part of the ciliary body passes into the choroid proper, adjacent to almost the entire inner surface of the sclera and consisting of vessels of different sizes, which contain about 80% of the blood that enters the eye. The iris, ciliary body and choroid together make up the middle layer of the eye, called the vascular tract. The inner shell of the eye - the retina - is the perceptive (receptive) apparatus of the eyes.
By anatomical structure The retina consists of ten layers, the most important of which is the layer of visual cells, consisting of light-perceiving cells - rod and cone cells, which also perceive color. They transform the physical energy of light rays entering the eyes into a nerve impulse, which is transmitted along the visual-nervous pathway to the occipital lobe of the brain, where the visual image is formed.
In the center of the retina there is an area of the macula, which provides the most subtle and differentiated vision. In the nasal half retina, approximately 4 mm from the macula, is the exit point of the optic nerve, forming a disk with a diameter of 1.5 mm. Vessels emerge from the center of the optic disc - an artery and a vein, which are divided into branches distributed over almost the entire surface of the retina. The cavity of the eye is filled with the lens and vitreous body.
The lenticular lens - one of the parts of the diopter apparatus of the eye - is located directly behind the iris; between its front surface and back surface the iris has a slit-like space - the posterior chamber of the eye; like the anterior one, it is filled with aqueous humor. The lens consists of a bag formed by the anterior and posterior capsules, inside of which are fibers that are layered one on top of the other. There are no vessels or nerves in the lens. The vitreous body, a colorless gelatinous mass, occupies most of the eye cavity. In front it is adjacent to the lens, on the side and behind - to the retina.
Movements of the eyeballs are possible thanks to an apparatus consisting of 4 rectus and 2 oblique muscles; they all start from the fibrous ring at the apex of the orbit (See Orbit) and, expanding in a fan-shaped manner, are woven into the sclera. Contractions of individual eye muscles or their groups provide coordinated eye movements. (L. A. Katsnelson)
Different colors of the normal iris
: 1 - muscle that lifts the upper eyelid; 2 - superior oblique muscle; 3 - superior rectus muscle; 4 - external rectus muscle; 5 - internal rectus muscle; 6 - optic nerve; 7 - inferior rectus muscle; 8 - inferior oblique muscle.
Fundus of the eye when examined with an ophthalmoscope: 1 - yellow spot; 2 - optic disc; 3 - retinal veins; 4 - retinal arteries.
: 1 - superior rectus muscle of the eye; 2 - muscle that lifts the upper eyelid; 3 - frontal sinus(frontal bone); 4 - lens; 5 - anterior chamber of the eye; 6 - cornea; 7 - upper and lower eyelids; 8 - pupil; 9 - iris; 10 - ligament of Zinn; 11 - ciliary body; 12 - sclera; 13 - choroid; 14 - retina; 15 - vitreous body; 16 - optic nerve; 17 - inferior rectus muscle of the eye.
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The structure of the human eye resembles a camera. The lens is the cornea, lens and pupil, which refract light rays and focus them on the retina. The lens can change its curvature and works like autofocus on a camera - instantly adjusts good vision near or far. The retina, like photographic film, captures the image and sends it in the form of signals to the brain, where it is analyzed.
1 -pupil, 2 -cornea, 3 -iris, 4 -lens, 5 -ciliary body, 6 -retina, 7 -choroid, 8 -optic nerve, 9 -blood vessels of the eye, 10 -eye muscles, 11 -sclera, 12 -vitreous.
The complex structure of the eyeball makes it very sensitive to various injuries, metabolic disorders and diseases.
Ophthalmologists of the portal "All about vision" plain language described the structure of the human eye, giving you a unique opportunity to visually familiarize yourself with its anatomy.
The human eye is a unique and complex paired sensory organ, thanks to which we receive up to 90% of the information about the world around us. Each person's eye has individual characteristics that are unique to him. But common features structures are important for understanding what an eye is like from the inside and how it works. During evolution, the eye has achieved a complex structure and structures of different tissue origins are closely interconnected in it. Blood vessels and nerves, pigment cells and connective tissue elements all provide the main function of the eye - vision.
The structure of the main structures of the eye
The eye has the shape of a sphere or ball, so the allegory of the apple began to be applied to it. The eyeball is a very delicate structure, therefore it is located in the bony cavity of the skull - the orbit, where it is partially hidden from possible damage. In front, the eyeball is protected by the upper and lower eyelids. Free movements of the eyeball are ensured by the external oculomotor muscles, the precise and coordinated work of which allows us to see the world two eyes, i.e. binocularly.Constant hydration of the entire surface of the eyeball is provided by the lacrimal glands, which ensure adequate production of tears, forming a thin protective tear film, and the outflow of tears occurs through special lacrimal ducts.
The most outer shell eyes - conjunctiva. It is thin and transparent and also lines the inner surface of the eyelids, providing easy gliding when the eyeball moves and the eyelids blink.
The outer “white” layer of the eye, the sclera, is the thickest of the three eye layers, protects the internal structures and maintains the tone of the eyeball.
The scleral membrane in the center of the anterior surface of the eyeball becomes transparent and has the appearance of a convex watch glass. This transparent part sclera is called the cornea, which is very sensitive due to the presence of many nerve endings. The transparency of the cornea allows light to penetrate into the eye, and its sphericity ensures the refraction of light rays. The transition zone between the sclera and the cornea is called the limbus. This zone contains stem cells that ensure constant regeneration of cells in the outer layers of the cornea.
The next layer is the choroid. It lines the sclera from the inside. From its name it is clear that it provides blood supply and nutrition to intraocular structures, and also maintains the tone of the eyeball. The choroid consists of the choroid itself, which is in close contact with the sclera and retina, and structures such as the ciliary body and iris, which are located in the anterior part of the eyeball. They contain many blood vessels and nerves.
The ciliary body is part of the choroid and a complex neuro-endocrine-muscular organ that plays important role in the production of intraocular fluid and in the process of accommodation.
The color of the iris determines the color of a person's eye. Depending on the amount of pigment in its outer layer, it ranges in color from pale blue or greenish to dark brown. In the center of the iris there is a hole - the pupil, through which light enters the eye. It is important to note that the blood supply and innervation of the choroid and iris with the ciliary body are different, which is reflected in the clinical picture of diseases of such a generally unified structure as the choroid.
The space between the cornea and the iris is the anterior chamber of the eye, and the angle formed by the periphery of the cornea and the iris is called the anterior chamber angle. Through this angle, the outflow of intraocular fluid occurs through a special complex drainage system into the eye veins. Behind the iris is the lens, which is located in front of the vitreous body. It has the shape of a biconvex lens and is well fixed by many thin ligaments to the processes of the ciliary body.
The space between the posterior surface of the iris, the ciliary body and the anterior surface of the lens and vitreous body is called the posterior chamber of the eye. The anterior and posterior chambers are filled with colorless intraocular fluid or aqueous humor, which constantly circulates in the eye and washes the cornea and lens, while nourishing them, since these eye structures do not have their own vessels.
The innermost, thinnest and most important membrane for the act of vision is the retina. It is a highly differentiated multilayer nerve tissue, which lines the choroid in its posterior section. The optic nerve fibers originate from the retina. It carries all the information received by the eye in the form of nerve impulses through a complex visual pathway to our brain, where it is converted, analyzed and perceived as objective reality. It is the retina that ultimately receives or does not receive the image, and depending on this, we see objects clearly or not very clearly. The most sensitive and thin part of the retina is the central region - the macula. It is the macula that provides our central vision.
The cavity of the eyeball is filled with a transparent, somewhat jelly-like substance - the vitreous body. It maintains the density of the eyeball and fits into the inner shell - the retina, fixing it.
Optical system of the eye
In its essence and purpose, human eye is a complex optical system. Several of the most important structures can be identified in this system. These are the cornea, lens and retina. Basically, the quality of our vision depends on the state of these structures that transmit, refract and perceive light, and the degree of their transparency.- The cornea refracts light rays more than any other structure, then passing through the pupil, which acts as a diaphragm. Figuratively speaking, as in good camera The diaphragm regulates the flow of light rays and, depending on the focal length, allows you to obtain a high-quality image, and the pupil functions in our eye.
- The lens also refracts and transmits light rays further to the light-receiving structure - the retina, a kind of photographic film.
- The fluid of the eye chambers and the vitreous body also have light-refracting properties, but not as significant. However, the condition of the vitreous body, the degree of transparency of the aqueous humor of the eye chambers, the presence of blood or other floating opacities in them can also affect the quality of our vision.
- Normally, light rays, having passed through all transparent optical media, are refracted so that when they hit the retina, they form a reduced, inverted, but real image.
Thus, the eye is very complex and amazing. A disruption in the condition or blood supply of any structural element of the eye can adversely affect the quality of vision.
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: the outer layer of the eye - the sclera and cornea, the middle layer - the choroid and lens, and the inner layer - the 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 structure of the eyeball
The structural diagram has the most complex structure after the brain. tunica albuginea represented by the sclera, which forms a spherical shape. It contains white fibrous tissue. This 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 presented choroid, which includes the vessels located in the back of the eyes, the iris and the ciliary body, consisting of many tiny fibers that form the ciliary girdle. 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.
Anatomy of the eyeball
The table characterizes the structure and functions of the eye with a description of the most important structural functions that activate all 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, changing 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.
Optical system and vision
Eye system. The human vision system is designed to refract and focus light. In this case, a tiny light image of a visible object appears in the posterior eye area, 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. The next regulating element of the visual description is the lens. With its help, light rays are fixed behind the retina, where the light-sensitive rods and cones are located, they transmit the 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.
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. Complexity visual signals, coming from the outside world, 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 in 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 a large number of blood vessels. In the anterior part of the eyeball, the 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 having the form of a biconvex lens. The lens is covered with a transparent bag; along its entire edge, thin, but very elastic fibers stretch to the ciliary body. They are strongly stretched and hold the lens in a stretched state. 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 rear cameras eyes. They contain clear liquid. It supplies nutrients to the cornea and lens, which lack 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 photosensitive cells, named for 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 muscle 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 clogging of the eyes and drying 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, along the lacrimal 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.
Nerves 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. With the complete destruction of the chiasm, bilateral blindness develops. 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 field of vision, 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. Atrophy of the optic nerve may be primary (with dorsal tabes, 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, and a narrowing of the field of vision.
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 muscle that lifts the upper eyelid, the muscle that constricts the pupil, the ciliary muscle, which regulates the configuration of the lens, which allows the eye to adapt to 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 colliculi 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 cell accessory nuclei, parasympathetic fibers are directed to the muscle constrictor pupil, 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. With the defeat of the core, "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 if the nucleus is damaged, the process is localized in the brain stem, then often in pathological process the pyramidal tract and fibers of the spinothalamic tract are involved, alternating Weber syndrome occurs, i.e. defeat 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 are of different sizes (anisocoria).
The oculomotor nerve, when leaving the cerebral peduncle, 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 whose function is to decompose all the complexity of the external and inner 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 "core" represents a detailed and precise projection in the cortex of all the elements of the peripheral receptor and is necessary for the implementation of 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 is of great importance for restoring 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 - fibers of ganglion cells, forming the optic nerve at the exit from the eyeball; 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 visual areas 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 - visual 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
