- one of the most important analyzers, because provides more than 90% of sensory information.
Visual perception begins with the projection of an image onto the retina and excitation of photoreceptors, then the information is sequentially processed in the subcortical and cortical visual centers, resulting in a visual image that, thanks to the interaction of the visual analyzer with other analyzers, correctly reflects objective reality.
Visual analyzer - a set of structures that perceive light radiation ( electromagnetic waves with a length of 390-670 nm) and forming visual sensations.
It allows you to distinguish between the illumination of objects, their color, shape, size, movement characteristics, and spatial orientation in the surrounding world.
The organ of vision consists of eyeball, optic nerve and auxiliary organs of the eye. The eye consists of optical and photoreceptive parts and has three membranes: albuginea, vascular and retina.
The optical system of the eye provides the light refractive function and consists of light refractive (refractive) media (refraction - for the purpose of focusing rays at one point on the retina): Transparent cornea(strong refractive power);
fluid of the anterior and posterior chambers;
lens surrounded by a transparent bag, implements accommodation - change in refraction;
vitreous body, occupying most of the eyeball (weak refractive power).
The eyeball has a spherical shape. It distinguishes the anterior and posterior poles. The anterior pole is the most protruding point of the cornea, the posterior pole is located lateral to the exit site optic nerve. The conventional line connecting both poles is the outer axis of the eye; it is equal to 24 mm and is located in the plane of the meridian of the eyeball. The eyeball consists of a nucleus (lens, vitreous body), covered with three membranes: outer (fibrous or albuginea), middle (vascular), internal (reticular).
Cornea- a transparent convex saucer-shaped plate, devoid of blood vessels. The different quantities and qualities of the melanin pigment on the pigment layer of the iris determine the color of the eye - brown, black (if there is a large amount of melanin), blue and greenish if there is little of it. Albinos have no pigment at all, their iris is not colored, they can be seen through it blood vessels and that is why the iris appears red.
Lens– transparent biconvex lens (i.e. magnifying glass) with a diameter of about 9 mm, having front and back surfaces. The front surface is flatter. The line connecting the most convex points of both surfaces is called the axis of the lens. The lens is, as it were, suspended on the ciliary band, i.e. on the ligament of zinn.
The curvature of the lens depends on the ciliary muscle, it tenses. When reading, when looking into the distance, this muscle relaxes, the lens becomes flat. When looking into the distance, the lens is less convex.
That. when the ligament is stretched, i.e. When the ciliary muscle relaxes, the lens flattens (set to far vision), when the ligament relaxes, i.e. when the ciliary muscle contracts, the convexity of the lens increases (setting for near vision) This is called accommodation.
The lens has the shape of a biconvex lens. Its function is to refract light rays passing through it and focus the image on the retina.
Vitreous body– a transparent gel consisting of extracellular fluid with collagen and hyaluronic acid in colloidal solution. Fills the space between the retina at the back, the lens and the back of the ciliary band at the front. On the anterior surface of the vitreous body there is a fossa in which the lens is located.
At the back of the eye, the inner surface is lined with the retina. The space between the retina and the dense sclera, surrounding the eyeball, is filled with a network of blood vessels - the choroid. At the posterior pole of the human eye, there is a small depression in the retina - the fovea - the place where visual acuity in daylight is maximum.
Retina is the inner (photosensitive) membrane of the eyeball, adjacent to the inside throughout choroid.
It consists of 2 sheets: the inner one is photosensitive, the outer one is pigmented. The retina is divided into two parts: the posterior one - visual and the anterior one - (ciliary) which does not contain photoreceptors.
The place where the optic nerve exits the retina is called the optic disc or blind spot. It does not contain photoreceptors and is insensitive to light. From the entire retina, nerve fibers converge to the optic spot, forming the optic nerve.
More laterally, at a distance of about 4 mm from the blind spot, a special area is isolated best vision - yellow spot(carotenoids are present).
There are no blood vessels in the macula area. In its center is the so-called fovea centralis, which contains cones.
It is the place of best vision of the eye. As you move away from the fovea, the number of cones decreases and the number of rods increases
There are 10 layers in the retina.
Let's consider the main layers: outer - photoreceptor (layer of rods and cones);
pigmented, the innermost, tightly adjacent directly to the choroid;
layer of bipolar and ganglion (axons make up the optic nerve) cells. Above the layer of ganglion cells are their nerve fibers, which, when collected together, form the optic nerve.
Light rays pass through all these layers.
The perception of light is carried out with the participation of photoreceptors, which belong to the secondary sensory receptors. This means that they are specialized cells that transmit information about light quanta to retinal neurons, first to bipolar neurons, then to ganglion cells, the information then goes to subcortical neurons (thalamus and anterior colliculus) and cortical centers (primary projection field 17 , secondary projection fields 18 19) of vision. In addition, horizontal and amocrine cells participate in the processes of information transmission and processing in the retina.
All retinal neurons form the nervous apparatus of the eye, which not only transmits information to the visual centers of the brain, but also participates in its analysis and processing. Therefore, it is called the part of the brain located in the periphery.
The receptor section of the visual analyzer consists of photoreceptor cells: rods and cones. In the retina of each human eye there are 6-7 million cones and 110-125 million rods. They are distributed unevenly in the retina.
The central fovea of the retina contains only cones. In the direction from the center to the periphery of the retina, their number decreases, and the number of rods increases. The cone apparatus of the retina functions in conditions of high illumination; they provide daytime and color vision; the rod apparatus is responsible for twilight vision. Cones perceive color, rods perceive light.
Photoreceptor cells contain light-sensitive pigments: rods contain rhodopsin, cones contain iodopsin.
Damage to the cones causes photophobia: a person sees in dim light, but goes blind in bright light. The absence of one of the types of cones leads to impaired color perception, i.e., color blindness. Impaired rod function, which occurs when there is a lack of vitamin A in food, causes twilight vision disorders - night blindness: a person goes blind at dusk, but sees well during the day.
A set of photoreceptors sending their signals to one ganglion cell forms it receptive field.
Color vision is the ability of the vision system to respond to changes in light wavelength with the formation of color perception.
Color is perceived by the action of light on the central fovea of the retina, where only the cones are located. As you move away from the center of the retina, color perception becomes worse. The periphery of the retina, where the rods are located, does not perceive color. At dusk due to sharp decline“cone” vision and the predominance of “peripheral” vision, we do not distinguish color. The field of view is the space that one eye sees with a fixed gaze.
Retinal neurons.
Retinal photoreceptors synapse with bipolar neurons.
Bipolar neurons are the first neuron of the conduction section of the visual analyzer. When exposed to light, the release of the transmitter (glutamate) from the presynaptic end of the photoreceptor decreases, which leads to hyperpolarization of the bipolar neuron membrane. From it, the nerve signal is transmitted to ganglion cells, the axons of which are the fibers of the optic nerve. Signal transmission from photoreceptors to the bipolar neuron and from it to the ganglion cell occurs in a pulseless manner. A bipolar neuron does not generate impulses due to the extremely short distance over which it transmits a signal.
The axons of ganglion cells form the optic nerve. Impulses from many photoreceptors converge (converge) through bipolar neurons to a single ganglion cell.
Photoreceptors connected to one ganglion cell form its receptive field of that cell.
THAT. each ganglion cell summarizes the excitation arising in a large number of photoreceptors. This increases light sensitivity but degrades spatial resolution. In the center of the retina, in the area of the fovea, each cone is connected to one dwarf bipolar cell, to which is connected to one ganglion cell. This provides high spatial resolution here and sharply reduces light sensitivity.
The interaction of neighboring retinal neurons is ensured by horizontal and amacrine cells, through the processes of which signals propagate that change synaptic transmission between photoreceptors and bipolar cells (horizontal) and between bipolar and ganglion cells (amacrine cells). Horizontal (stellate) and amacrine cells play an important role in the processes of analysis and synthesis in retinal neurons. Up to hundreds of bipolar cells and receptors converge on one ganglion cell.
FROM the retina (bipolar cells transmit signaling to retinal ganglion cells, the axons of which run as part of the right and left optic nerves), visual information along the fibers of the optic nerve (2nd pair of cranial nerves) rushes to the brain. The optic nerves from each eye meet at the base of the brain, where their partial decussation or chiasm is formed. Here, part of the fibers of each optic nerve passes to the side opposite to its eye. Partial decussation of fibers provides each hemisphere of the brain with information from both eyes. The occipital lobe of the right hemisphere receives signals from the right halves of each retina, and in left hemisphere- from the left halves of the retinas.
After the optic chiasm, I call the optic nerves OPTIC TRACTS. They are projected into a number of brain structures. Each optic tract contains nerve fibers coming from the inner region of the retina of the eye of the same side and from the outer half of the retina of the other eye. After crossing the fibers of the optic tract heading towards the outside geniculate bodies of the thalamus, where impulses are switched to neurons, the axons of which are sent to the cerebral cortex to the primary projection area of the visual cortex (striate cortex or Brodmann's 17th area), then to the secondary projection area (areas 18 and 19, prestiary cortex), and then – into the association zones of the cortex. The cortical department of the visual analyzer is located in occipital lobe(17,18,10th fields according to Brodmann). The primary projection area (17th field) carries out specialized, but more complex than in the retina and lateral geniculate bodies, information processing. In each area of the cortex, neurons are concentrated, which form a functional column. Some of the fibers from the ganglion cells go to the neurons of the superior colliculi and the roof of the midbrain, to the pretectal region and the pillow in the thalamus (from the pillow it is transmitted to the area of the 18th and 19th fields of the cortex).
The pretectal region is responsible for regulating the diameter of the pupil, and the anterior tubercles of the quadrigeminal are associated with the oculomotor centers and higher parts of the visual system. Neurons of the anterior colliculi provide the implementation of orienting (sentinel) visual reflexes. From the anterior tubercles, impulses go to the nuclei of the oculomotor nerve, which innervate the muscles of the eye, the ciliary muscle and the muscle that constricts the pupil. Due to this, in response to light waves entering the eye, the pupil narrows, and the eyeballs turn in the direction of the light beam.
Part of the information from the retina along the optic tract enters the suprachiasmatic nuclei of the hypothalamus, ensuring the implementation of circadian biorhythms.
Color vision.
Most people are able to distinguish between primary colors and their many shades. This is explained by the effect on photoreceptors of electromagnetic oscillations of different wavelengths.
Color vision– the ability of the visual analyzer to perceive light waves of different lengths. Color is perceived by the action of light on the central fovea of the retina, where exclusively cones are located (perceived in the blue, green, red range). As you move away from the center of the retina, color perception becomes worse. The periphery of the retina, where the rods are located, does not perceive color. At dusk, due to a sharp decrease in “cone” vision and the predominance of “peripheral” vision, we do not distinguish color.
A person who has all three types of cones (red, green, blue), i.e. trichromate, has normal color perception. The absence of one type of cone leads to impaired color perception. At dusk, due to a sharp decrease in “cone” vision and the predominance of “peripheral” vision, we do not distinguish color.
Color blindness is expressed in the loss of perception of one of the components of three-color vision. Its occurrence is associated with the absence of certain genes on the unpaired sex chromosome in men. (Rabkin tables - polychromatic tables). Achromasia is complete color blindness resulting from damage to the cone apparatus of the retina. Moreover, all objects are seen by a person only in different shades gray color.
Protanopia “red-blind” - do not perceive red color, blue-blue rays appear colorless. Deuteranopia - “green-blind” - do not distinguish green colors from dark red and blue; Trtanopia - violet-blind, do not perceive blue and violet colors.
Binocular vision- this is the simultaneous vision of objects with both eyes, which gives a more pronounced sense of the depth of space compared to monocular vision (i.e. vision with one eye). Due to the symmetrical arrangement of the eyes.
Accommodation – adjustment of the optical apparatus of the eye to a certain distance, as a result of which the image of an object is focused on the retina.
Accommodation is the adaptation of the eye to clearly seeing objects at different distances from the eye. It is this property of the eye that allows you to see objects that are close or far away equally well. In humans, accommodation is carried out by changing the curvature of the lens - when viewing distant objects, the curvature decreases to a minimum, and when viewing nearby objects, its curvature increases (convex).
Refractive errors.
Lack of necessary focusing of the image on the retina interferes with normal vision.
Myopia (nearsightedness) is a type of refractive error in which rays from an object, after passing through a light-refracting apparatus, are focused not on the retina, but in front of it - in vitreous body, i.e. the main focus is in front of the retina due to the increase in the longitudinal axis. The longitudinal axis of the eye is too long. In this case, the person’s perception of distant objects is impaired. Correction of such a disorder is carried out using biconcave lenses, which push back the focused image on the retina.
For hypermetropia (farsightedness)- rays from distant objects, due to the weak refractive power of the eye or the short length of the eyeball, are focused behind the retina, i.e. the main focus is behind the retina due to the short longitudinal axis of the eye. In the farsighted eye longitudinal axis eyes are shortened. This refractive error can be compensated by increasing the convexity of the lens. Therefore, a farsighted person strains the accommodative muscle, examining not only close, but also distant objects.
Astigmatism (unequal refraction of rays in different directions) – This is a type of refractive error in which there is no possibility of rays converging at one point of the retina, due to different curvature of the cornea in different parts of it (in different planes), as a result of which the main focus in one place may fall on the retina, in another it may be in front of it or behind it, which distorts the perceived image.
Defects in the optical system of the eye are compensated by combining the main focus of the refractive media of the eye with the retina.
In clinical practice they use spectacle lenses: for myopia – biconcave (diverging) lenses; for hypermetropia - biconvex (collective) lenses; for astigmatism - cylindrical lenses with different refractive powers in different areas.
Aberration– distortion of the image on the retina caused by the peculiarities of the refractive properties of the eye for light waves of different lengths (diffraction, spherical, chromatic).
Spherical aberration- unequal refraction of rays in the central and peripheral parts of the cornea and lens, which will lead to scattering of rays and a sharp image.
Visual acuity - the ability to see two points that are as close as possible as different, i.e. the smallest angle of vision at which the eye is able to see two points separately. The angle between the incidence of rays = 1 (second). In practical medicine, visual acuity is indicated in relative units. With normal vision, visual acuity = 1. Visual acuity depends on the number of excitable cells.
Hearing analyzer
- is a combination of mechanical, receptor and nerve structures, perceiving and analyzing sound vibrations. Sound signals are vibrations of air with different frequencies and strengths. They stimulate the auditory receptors located in the cochlea of the inner ear. The receptors activate the first auditory neurons, after which sensory information is transmitted to the auditory area of the cerebral cortex.
In humans, the auditory analyzer is represented by the peripheral section (outer, middle, inner ear), wiring department, cortical (temporal auditory cortex)
Binaural hearing – the ability to hear simultaneously with both ears and determine the location of the sound source.
Sound is the oscillatory movements of particles of elastic bodies, propagating in the form of waves in a variety of media, including air, and perceived by the ear. Sound waves are characterized by frequency and amplitude. The frequency of sound waves determines the pitch of the sound. The human ear distinguishes sound waves with a frequency from 20 to 20,000 Hz. Sound waves that have harmonic vibrations are called tone. Sound consisting of unrelated frequencies is noise. When the frequency of sound waves is high, the tone is high, and when the frequency is low, it is low.
The sounds of spoken language have a frequency of 200-1000 Hz. Low frequencies make up the bass singing voice, high frequencies make up the soprano voice.
The unit for measuring sound volume is the decibel. The harmonic combination of sound waves forms the timbre of sound. By timbre, you can distinguish sounds of the same height and volume, which is the basis for recognizing people by voice.
The peripheral part in humans is morphologically combined with the peripheral part of the vestibular analyzer and is therefore called the organ of hearing and balance.
Outer ear is a sound-collecting device. It consists of auricle and outdoor ear canal, which is separated by the eardrum from the middle one.
Auricle ensures the capture of sounds, their concentration in the direction of the external auditory canal and an increase in their intensity.
External auditory canal conducts sound vibrations to the eardrum, separating the outer ear from the tympanic cavity or middle ear. Vibrates when exposed to sound waves.
The external auditory canal and middle ear are separated by the eardrum.
From a physiological point of view, it is a weakly extensible membrane. Its purpose is to transmit sound waves that have reached it through the external auditory canal, accurately reproducing their strength and vibration frequency.
Middle ear
consists of a tympanic cavity (filled with air), in which three auditory ossicles are located: the malleus, the incus, and the stapes.
The handle of the malleus is fused with the eardrum; its other part is articulated with the incus, which acts on the stapes, which transmits vibration to the membrane of the oval window. Vibrations of the eardrum of reduced amplitude but increased strength are transmitted to the stapes. The area of the oval window is 22 times smaller than the tympanic membrane, increasing its pressure on the membrane of the oval window by the same amount. Even weak waves acting on the eardrum can overcome the resistance of the membrane of the oval window of the vestibule and lead to vibrations of the oval window of the fluid in the cochlea.
In the middle ear cavity the pressure is equal to atmospheric pressure. This is achieved due to the presence of the eustachian tube, which connects the tympanic cavity to the pharynx. When swallowing, the Eustachian tube opens and the pressure in the middle ear equalizes atmospheric pressure. This is important when sudden change pressure - during takeoff and landing of an airplane, in a high-speed elevator, etc. Timely opening of the Eustachian tube helps equalize pressure, relieves discomfort and prevents rupture of the eardrum.
It contains the receptor apparatus of 2 analyzers: vestibular (vestibule and semicircular canals) and auditory, which includes the cochlea with the organ of Corti. The inner ear is located in a pyramid temporal bone.
In inner ear located snail containing auditory receptors. The cochlea is a spirally twisted bone canal with 2.5 turns, almost to the very end of the cochlea, the bone canal is divided by 2 membranes: a thinner one - the vestibular membrane (Reisner's membrane) and a dense and elastic one - the main membrane. At the apex of the cochlea, both of these membranes are connected, and they contain the oval opening of the cochlea - the helicotrema. The vestibular and basilar membranes divide the bony canal of the cochlea into 3 passages: upper, middle, lower. The upper canal of the cochlea connects to the lower canal (scala tympani) Upper and lower channels The cochlea is filled with perilymph. Between them there is a middle canal; the cavity of this canal does not communicate with the cavity of other canals and is filled with endolymph. Inside the middle canal of the cochlea, on the main membrane, there is a sound-receiving apparatus - the spiral (corti) organ containing receptor hair cells. The tectorial membrane is located above the hairs of the receptor cells. When touched (as a result of vibrations of the main membrane), the hairs are deformed and this leads to the emergence of a receptor potential. These cells transform mechanical vibrations into electrical potentials.
Sound waves cause vibrations of the eardrum, which through the system auditory ossicles the middle ear and the membrane of the oval window are transmitted to the perilymph of the vestibular and tympanic scalae. This leads to vibrations of the endolymph and certain areas of the main membrane. High frequency sounds cause the membranes located closer to the base of the cochlea to vibrate. A receptor potential arises in the receptor cells, under the influence of which APs are generated in the endings of the auditory nerve fibers, which are transmitted further along the pathways.
Thus, sound perception is carried out with the participation of phonoreceptors. Their excitation under the influence of a sound wave leads to the generation of a receptor potential, which causes excitation of the dendrites of the bipolar neuron of the spiral ganglion.
Let's consider how frequency and sound strength are encoded?
For the first time in 1863, G. Helmholtz tried to explain the processes of encoding the frequency of a sound signal in the inner ear. He formulated the resonance theory of hearing, which is based on the so-called principle of place.
According to Helmholtz, the transverse fibers of the basilar membrane respond to sounds of unequal frequencies according to the principle of resonance. The basilar membrane can act as a set of transversely stretched elastic resonating bands, like the strings of a piano (the shortest ones, in the narrow part near the base of the cochlea, resonate in response to high frequencies, and those closer to the top, in the widened part of the basilar membrane, resonate in response to high frequencies). lowest frequencies). Accordingly, phonoreceptors are excited by these areas.
However, in the 50-60s of the 20th century, the initial premises of Helmholtz's resonance theory were rejected by G. Bekesy. Without rejecting the original principle of place, Bekesy formulated the traveling wave theory, according to which, when the membrane oscillates, waves travel from its base to the top. According to Bekesy, a traveling wave has the greatest amplitude in a strictly defined area of the membrane, depending on frequency.
When exposed to tones of a certain frequency, not one fiber of the main membrane vibrates (as Helmholtz assumed), but an entire section of this membrane. The resonating substrate is not the fiber of the main membrane, but a column of liquid of a certain length: the higher the sound, the shorter the length of the oscillating column of liquid in the canals of the cochlea and the closer to the base of the cochlea and the oval window is the maximum amplitude of vibration and vice versa.
When fluid oscillates in the canals of the cochlea, it is not individual fibers of the main membrane that react, but larger or smaller sections of it, and therefore, different numbers of receptor cells located on the membrane are excited.
The sensation of sound also occurs when a vibrating object, such as a tuning fork, is placed directly on the skull, in which case the bulk of the energy is transferred to the bones of the latter (bone conduction). To excite the receptors of the inner ear, fluid movement of the type caused by vibrations of the stapes is necessary when sound propagates through the air. Sound transmitted through the bones of the skull causes such movement in two ways: firstly, waves of compression and rarefaction, passing through the skull, displace fluid from the voluminous vestibular labyrinth into the cochlea, and then back (compression theory). Secondly, the mass of the tympanic-ossicular apparatus and the inertia associated with it lead to its vibrations lagging behind those characteristic of the bones of the skull. As a result, the stirrup moves relative to petrous bone, exciting the inner ear (mass-inertial theory).
Conductor section of the hearing analyzer begins with a peripheral bipolar neuron located in the spiral ganglion of the cochlea. The auditory nerve fibers end on the cells of the nuclei of the cochlear complex medulla oblongata(second neuron). Then, after partial decussation, the fibers go to the medial geniculate body of the thalamus, where again a switch occurs to the third neuron, from which information enters the cortex. The cortical section of the auditory analyzer is located in the upper part of the temporal gyrus of the cerebrum (fields 41, 42 according to Boardman) - this is the highest acoustic center where cortical analysis of sound information is carried out.
Along with the ascending pathways, there are also descending ones, ensuring control of higher acoustic centers over the receipt and processing of information in the peripheral and conductive sections of the auditory analyzer.
These pathways begin from the cells of the auditory cortex, switch sequentially in the medial geniculate body, posterior colliculus, superior olivary complex, from which the olivocochlear bundle of Rasmussen extends, reaching the hair cells of the cochlea.
In addition, there are efferent fibers coming from the primary auditory zone, i.e. from the temporal region, to the structures of the extrapyramidal motor system (basal ganglia, septum, superior colliculus, red nucleus, substantia nigra, some nuclei of the thalamus, brainstem RF) and the pyramidal system.
These data indicate the involvement of the auditory sensory system in the regulation of human motor activity.
Echolocation is a type of acoustic orientation, characteristic of animals in which the functions of the visual analyzer are limited or completely eliminated. They have special organs - biosonars for sound generation. In bats, this is the frontal protuberance, the melon.
Blind people have an analogue of the echolocation ability of animals. It is based on a sense of obstacle. It is based on the fact that a blind person has very acute hearing. Therefore, he subconsciously perceives sounds reflected from objects that accompany his movement. When their ears are closed, this ability disappears.
Methods for studying the auditory analyzer.
Speech audiometry is designed to study the sensitivity of the auditory analyzer (hearing acuity) with whispered speech - the subject is at a distance of 6 m, turning to the researcher with an open ear, he must repeat the words pronounced by the researcher in a whisper. With normal hearing acuity, whispered speech is perceived at a distance of 6-12 m.
Tuning fork audiometry.
(Rinne test and Weber test) is intended for a comparative assessment of air and bone conduction of sound by perceiving a sounding tuning fork. In a healthy person, air conduction is higher than bone conduction.
In the Rinne test, the stem of a sounding tuning fork is placed on mastoid process. Upon completion of the perception of sound, the jaws of the tuning fork are brought to the sound passage - a healthy person continues to perceive the sound of the tuning forks. In humans, when using C128 time air conduction 75s, and bone - 35.
Olfactory analyzer.
The olfactory analyzer allows you to determine the presence of odorous substances in the air. It helps to orient the body in environment and, together with other analyzers, the formation of a number of complex forms of behavior (eating, defensive, sexual).
The surface of the nasal mucosa is enlarged due to the nasal turbinates - ridges protruding from the sides into the lumen of the nasal cavity. The olfactory area, containing most of the sensory cells, is limited here by the superior turbinate.
The receptors of the olfactory system are located in the area of the upper nasal passages. The olfactory epithelium is located away from the main respiratory tract, has a thickness of 100-150 µm and contains receptor cells located between the supporting cells. On the surface of each olfactory cell there is a spherical thickening - the olfactory club, from which protrudes 6-12 thinnest hairs (cilia), in the membranes of which there are specific proteins - receptors. These cilia are not able to actively move, because immersed in a layer of mucus covering the olfactory epithelium. Odorous substances brought by inhaled air come into contact with their membrane, which leads to the formation of a receptor potential in the dendrite of the olfactory neuron, and then the emergence of AP in it. Olfactory cilia are immersed in a liquid medium produced by the olfactory (Bowman's) glands. Throughout the mucosa there are still free endings of the trigeminal nerve, some of which react to smell.
In the pharynx, olfactory stimuli are able to excite fibers of the glossopharyngeal and vagus nerves.
Olfactory receptor- this is a primary bipolar sensory cell, from which two processes extend: from the top there is a dendrite bearing cilia, and from the base an unmyelinated axon extends. The receptor axons form the olfactory nerve, which penetrates the base of the skull and enters the olfactory bulb (in the cortex of the ventral surface of the frontal lobe). Olfactory cells are constantly renewed. Their lifespan is 2 months. The smell is perceived only when the nasal mucosa is moistened. The impulse is transmitted along the olfactory nerve to the olfactory bulb (primary center), where the image is already formed.
Molecules of odorous substances enter the mucus produced by the olfactory glands with a constant flow of air or from the oral cavity during eating. Sniffing accelerates the flow of odorous substances to the mucus. In mucus, molecules of odorous substances are a short time bind to non-receptor proteins. Some molecules reach the olfactory receptor cilia and interact with the olfactory receptor protein located in them. The olfactory protein activates GTP-binding protein, which in turn activates the enzyme adenylate cyclase, which synthesizes cAMP. An increase in the concentration of cAMP in the cytoplasm causes the opening of sodium channels in the plasma membrane of the receptor cell and, as a consequence, the generation of a depolarizing receptor potential. This leads to an impulse discharge in the axon (olfactory nerve fiber).
Each receptor cell is capable of responding with physiological excitation to its characteristic spectrum of odorants.
Each olfactory cell has only one type of membrane receptor protein. This protein itself is capable of binding many odorous molecules.
Each olfactory receptor responds not to one, but to many odorous substances, giving “preference” to some of them.
Afferent fibers do not switch in the thalamus and do not travel to the opposite side of the brain.
One olfactory receptor can be excited by one molecule odoriferous substance, and the stimulation of a small number of receptors leads to the sensation. At low concentrations of an odorous substance, a person only perceives the odor and cannot determine its quality (detection threshold). At higher concentrations, the smell of the substance becomes recognizable and a person can identify it (identification threshold). With prolonged exposure to the odor stimulus, the sensation weakens and adaptation occurs. There is an emotional component to a person’s olfactory perception. The smell can cause feelings of pleasure or disgust and at the same time the person’s state changes.
The influence of smell on other functional systems.
A direct connection with the limbic system explains the pronounced emotional component of olfactory sensations. Smells can cause pleasure or disgust, affecting the affective state of the body accordingly. Olfactory stimuli have the significance of olfactory stimuli in the regulation of sexual behavior.
Occurs in humans the following types of smell disorders: anosmia – lack of olfactory sensitivity; hyposmia – decreased sense of smell; hyperosmia – its increase; parosmia – incorrect perception of odors; Olfactory agnosia - a person smells a smell, but does not recognize it. Olfactory hallucinations occur when there are olfactory sensations in the absence of odorous substances. This can be due to head injuries, allergic rhinitis, and schizophrenia.
Electroolfactogram is the total electrical potential recorded from the surface of the olfactory epithelium.
Taste analyzer.
The taste analyzer provides the appearance of taste sensations. Its main purpose is both to evaluate the taste properties of food and to determine its suitability for consumption, as well as to form appetite and influence the digestion process. They affect the secretion of the digestive glands.
Chemoreception plays an important role in the formation of taste sensations. Taste buds carry information about the nature and concentration of substances entering the mouth.
Taste receptors (taste buds) are located on the tongue, back wall pharynx, soft palate, tonsils and epiglottis. Most of them are on the tip, edges and back of the tongue. The taste bud has a flask shape. The taste bud does not reach the surface of the mucous membrane of the tongue and is connected to the oral cavity through the taste pore. The glands located between the papillae secrete a liquid that washes the taste buds.
In adults, sensory taste cells are located on the surface of the tongue. Taste cells are the shortest-living epithelial cells in the body: on average, after 250 hours, an old cell is replaced by a young one. In the narrow part of the taste bud there are microvilli of receptor cells on which chemoreceptors are located. They come into contact with the fluid contents of the oropharynx through a small opening in the mucous membrane called the taste pore.
Taste cells generate a receptor potential when stimulated. This excitation is synaptically transmitted to the afferent fibers of the FM nerves, which conduct it to the brain in the form of impulses.
Afferent fibers (bipolar neurons) that conduct excitation from taste buds are represented by nerves - the chorda tympani (branch of the facial nerve, VII), which innervates the anterior and lateral parts of the tongue, as well as the glossopharyngeal nerve, which innervates the back of the tongue. Afferent taste fibers are combined into a solitary tract, which ends in the corresponding nucleus of the medulla oblongata.
In it, the fibers form synapses with second-order neurons, the axons of which are directed to the ventral thalamus (the third neurons of the conduction section of the taste analyzer are located here), as well as the centers of salivation, chewing, and swallowing in the brain stem. The fourth neurons of the taste analyzer are localized in the cerebral cortex in the lower part of the somatosensory zone in the area of the tongue (postcentral gyrus of the cerebral cortex). As a result of information processing at the above levels, the number of neurons with highly specific taste sensitivity increases. A number of cortical cells respond only to substances with one taste quality. The location of such neurons indicates a high degree of spatial organization of the sense of taste.
Most of these neurons are multipolar. They respond to taste, temperature, mechanical and nociceptive stimuli, i.e. respond not only to taste, but also to temperature and mechanical stimulation of the tongue.
Human taste sensitivity.
Human distinguishes four main taste qualities: sweet, sour, bitter, salty.
In most people, certain parts of the tongue have unequal sensitivity to substances of different taste qualities: the tip of the tongue is most sensitive to sweet, the side surfaces to salty and sour, the root (base) to bitter.
Sensitivity to bitter substances is significantly higher. Since they are often poisonous, this feature warns us against danger, even their concentration in water and food is very low. Strong bitter irritants easily cause vomiting or the urge to vomit. Table salt in low concentration seems sweet, it becomes purely salty only when it is increased. THAT. the perceived quality of a substance depends on its concentration.
Taste perception depends on a number of factors. In conditions of hunger, there is an increased sensitivity of taste buds to various flavoring substances; when satiated, it decreases after eating. This reaction is the result of reflex influences from the receptors of the stomach, and is called the GASTROLINGUAL REFLEX. In this reflex, taste buds act as effectors.
The biological role of taste is not only to test the edibility of food; also affect digestion processes. Connections with autonomic efferents allow taste sensations influence the secretion of the digestive glands, not only on its intensity, but also on its composition, depending, for example, on whether sweet and salty substances predominate in food.
Taste perception changes with emotional arousal and with a number of diseases.
With age, the ability to distinguish taste decreases. This is also caused by the consumption of biologically active substances such as caffeine and heavy smoking.
Disorders of taste perception are distinguished: ageusia - loss or absence of taste sensitivity; hypogeusia - its decrease; hypergeusia - its increase; Dysgeusia is a disorder of the subtle analysis of taste sensations.
Vestibular (statokinetic) analyzer.
To assess the direction of action of the gravitational field, i.e. to determine the position of the body in three-dimensional space, vestibular analyzer.
Provides the perception of information about linear and rotational accelerations of body movement and changes in the position of the head in space, as well as about the effect of gravity. Important role belongs to the spatial orientation of a person during active and passive movement, maintaining posture and regulating movements.
During active movements, the vestibular system receives, transmits, analyzes information about accelerations and decelerations that occur in the process of linear and rotational movement, when the head and space change.
During passive movement cortical sections remember the direction of movement, turns, distance traveled.
Under normal conditions spatial orientation is ensured by the joint activity of the visual and vestibular systems.
With uniform movement or under resting conditions, the receptors of the vestibular sensory system are not excited.
In general, all information coming from the vestibular apparatus to the brain is used to regulate posture and locomotion, i.e. in the control of skeletal muscles.
The man has it peripheral section represented by the vestibular apparatus.
The peripheral (receptive) section of the analyzer is represented two types of receptor hair cells of the vestibular organ. It is located together with the cochlea in the labyrinth of the temporal bone and consists of the vestibule and three semicircular canals. The cochlea contains auditory receptors.
The vestibule includes two sacs: spherical (sacculus) and elliptical or utricle (utriculus). The semicircular canals are located in three mutually perpendicular planes. They open at their mouths into the vestibule. One of the ends of each channel is expanded (ampulla). All these structures form a membranous labyrinth filled with endolymph. Between the membranous and bony labyrinth there is perilymph. In the sacs of the vestibule there is an otolithic apparatus: a cluster of receptor cells (secondary sensory mechanoreceptors) on elevations or spots. In the ampoules of the semicircular canals there are scallops (cristae). Spots and scallops contain receptor cells epithelial cells having thin numerous (40-60 pieces) hairs (stereocilia) and one thicker and longer hair (kinocilia) on the free surface.
The receptor cells of the vestibule are covered with an otolithic membrane - a jelly-like mass of mucopolysaccharoids containing a significant amount of calcium carbonate crystals (otoliths). In the ampoules, the jelly-like mass does not contain otoliths and is called a leaf-shaped membrane. The hairs (cilia) of the receptor cells are immersed in these membranes.
Excitation of hair cells occurs when stereocilia bend towards kinocilia, which leads to the opening of mechanosensitive ion (potassium) channels (K ions from the endolymph enter the cytoplasm along a concentration gradient). The result of this entry of K ions is depolarization of the membrane. A receptor potential arises, which leads to the release of ACh at the synapses that exist between hair cells and the dendrites of afferent neurons. This is accompanied by an increase in the frequency of nerve impulses going to the vestibular nuclei of the medulla oblongata.
When the stereocilia are displaced in the opposite direction from the kinocilia, the ion channels close, the membrane hyperpolarizes, and the activity of the vestibular nerve fiber decreases.
An adequate stimulus for the receptor cells of the vestibule are linear accelerations and tilts of the head or the entire body, leading to the sliding of the otolith membranes under the influence of gravity and a change in the position (bending) of the hairs. For the receptor cells of the ampullae of the semicircular canals, an adequate stimulus is angular acceleration in different planes when turning the head or rotating the body.
The conductive section of the vestibular analyzer is presented afferent and efferent fibers.
The first neuron to sense excitation of hair cells vestibular apparatus, are bipolar neurons, form the basis of the vestibular ganglion (Scarpe's ganglion), which lies at the bottom of the internal auditory canal. Their dendrites, in contact with hair cells, in response to excitations of these receptor cells, generate APs, which are transmitted along the axon to the CNS along the axons. The axons of bipolar cells form the vestibular or vestibular part of the 8 pair of cranial nerves. Spontaneous electrical activity is observed in the vestibular nerve at rest. The frequency of discharges in the nerve increases when the head is turned in one direction and slows down when the head is turned in the other direction.
Afferent fibers (fibers of the vestibular part of the nerve) are sent to the vestibular nuclei of the medulla oblongata, from them to the thalamus, in which impulses are switched to the next afferent neuron, which conducts impulses directly to the neurons of the cerebral cortex.
The vestibular nuclei of the medulla oblongata are connected with all parts of the central nervous system: the spinal cord, cerebellum, RF of the brain stem, oculomotor nuclei, cerebral cortex, and autonomic nervous system. There are 5 projection systems.
A wonderful world full of colors, sounds and smells is given to us by our senses.
M.A. OSTROVSKY
The purpose of the lesson: study of the visual analyzer.
Tasks: definition of the concept of “analyzer”, study of the analyzer’s operation, development of experimental skills and logical thinking, development of creative activity of students.
Lesson type: presentation of new material with elements of experimental activity and integration.
Methods and techniques: search, research.
Equipment: fake eyes; table “Structure of the eye”; homemade tables “Direction of rays”, “Rods and cones”; handout: cards depicting the structure of the eye, visual impairments.
During the classes
I. Updating knowledge
The desired vault of the steppe sky.
Jets of steppe air,
On you I am in breathless bliss
Stopped my eyes.Look at the stars: there are many stars
In the silence of the night
Burns and shines around the moon
In the blue sky.E. Baratynsky
The wind brought from afar
Songs of spring hint,
Somewhere light and deep
A piece of sky opened up.
What images the poets created! What allowed them to be formed? It turns out that analyzers help with this. We will talk about them today. The analyzer is a complex system, providing analysis of irritations. How do irritations arise and where are they analyzed? Receivers external influences– receptors. Where does the irritation go next and what happens when it is analyzed? ( Students express their opinions.)
II. Learning new material
The irritation is converted into a nerve impulse and travels along the nerve pathway to the brain, where it is analyzed. ( Simultaneously with the conversation, we draw up a reference diagram, then discuss it with the students.)
What is the role of vision in human life? Vision is necessary for labor activity, for learning, for aesthetic development, for transmission social experience. We receive approximately 70% of all information through vision. The eye is the window to the world. This organ is often compared to a camera. The role of the lens is performed by the lens. ( Demonstration of dummies, tables.) The lens aperture is the pupil, its diameter changes depending on the lighting. Just like on a photographic film or photosensitive matrix of a camera, an image appears on the retina of the eye. However, the vision system is more advanced than a conventional camera: the retina and the brain themselves correct the image, making it clearer, more voluminous, more colorful and, finally, meaningful.
Familiarize yourself with the structure of the eye in more detail. Look at the tables and models, use the illustrations in the textbook.
Let's draw a diagram of the “Structure of the eye”.
Fibrous membrane
Posterior – opaque – sclera
Anterior – transparent – cornea
Choroid
Anterior – iris, contains pigment
In the center of the iris is the pupil
Lens
Retina
Brows
Eyelids
Eyelashes
Tear duct
Lacrimal gland
Oculomotor muscles
“A tight fishing net, thrown to the bottom of the eye glass and catching Sun rays! – this is how the ancient Greek physician Herophilus imagined the retina of the eye. This poetic comparison turned out to be surprisingly accurate. Retina– precisely a network, and one that catches individual quanta of light. It resembles a layer cake 0.15–0.4 mm thick, each layer is a multitude of cells, the processes of which intertwine and form an openwork network. Long processes extend from the cells of the last layer, which, gathering in a bundle, form optic nerve.
More than a million fibers of the optic nerve carry information to the brain encoded by the retina in the form of weak bioelectric impulses. The place on the retina where the fibers converge into a bundle is called blind spot.
The layer of the retina formed by light-sensitive cells - rods and cones - absorbs light. It is in them that the transformation of light into visual information occurs.
We got acquainted with the first link of the visual analyzer - receptors. Look at the picture of light receptors, they are shaped like rods and cones. Rods provide black and white vision. They are about 100 times more sensitive to light than cones and are arranged so that their density increases from the center to the edges of the retina. Visual pigment sticks absorb blue-blue rays well, but red, green and violet rays poorly. Color vision provide three types of cones, which are sensitive to violet, green and red colors, respectively. Opposite the pupil on the retina is the largest concentration of cones. This place is called yellow spot.
Remember the red poppy and blue cornflower. During the day they are brightly colored, and at dusk the poppy is almost black, and the cornflower is whitish-blue. Why? ( Students express opinions.) During the day, in good lighting, both cones and rods work, and at night, when there is not enough light for the cones, only the rods. This fact was first described by the Czech physiologist Purkinje in 1823.
Experiment "Rod Vision". Take a small object, such as a pencil, colored red, and, looking straight ahead, try to see it with your peripheral vision. The object must be continuously moved, then it will be possible to find a position in which the red color will be perceived as black. Explain why the pencil is positioned so that its image is projected onto the edge of the retina. ( There are almost no cones at the edge of the retina, and the rods do not distinguish color, so the image appears almost black.)
We already know that the visual zone of the cerebral cortex is located in the occipital part. Let's make a reference diagram " Visual analyzer».
Thus, the visual analyzer is a complex system for perceiving and processing information about the external world. The visual analyzer has large reserves. The retina of the eye contains 5–6 million cones and about 110 million rods, and the visual cortex of the cerebral hemispheres contains approximately 500 million neurons. Despite the high reliability of the visual analyzer, its functions can be disrupted under the influence of various factors. Why does this happen and what changes does it lead to? ( Students express their opinions.)
Please note that with good vision, the image of objects at a distance best vision(25 cm), is formed exactly on the retina. In the picture in the textbook you can see how the image is formed in a nearsighted and farsighted person.
Myopia, farsightedness, astigmatism, color blindness are common visual impairments. They may be hereditary, but they may also be acquired during life due to wrong mode labor, poor lighting on the desktop, non-compliance with safety rules when working on a PC, in workshops and laboratories, when watching TV for a long time, etc.
Studies have shown that after 60 minutes of continuous sitting in front of the TV, a decrease in visual acuity and the ability to distinguish colors occurs. Nerve cells They find themselves “overloaded” with unnecessary information, as a result of which memory deteriorates and attention weakens. IN last years registered special shape dysfunction nervous system– photoepilepsy, accompanied by convulsive seizures and even loss of consciousness. In Japan, on December 17, 1997, a massive attack of this disease was registered. As it turned out, the reason was the faster flashing of images in one of the scenes of the cartoon “Little Monsters”.
III. Consolidation of what has been learned, summing up, grading
Visual analyzer- this is a complex system of organs, which consists of a receptor apparatus represented by the organ of vision - the eye, conductive pathways and the final section - the perceptive areas of the cerebral cortex. The receptor apparatus includes, first of all, eyeball, which is formed by various anatomical formations. So, it consists of several shells. The outer shell is called sclera, or tunica albuginea. Thanks to it, the eyeball has a certain shape and is resistant to deformation. At the front of the eyeball is cornea, which, unlike the sclera, is completely transparent.
The choroid of the eye is located under the tunica albuginea. In its anterior part, deeper than the cornea, there is iris. In the center of the iris there is a hole - the pupil. The concentration of pigment in the iris is the determining factor for such a physical indicator as eye color. In addition to these structures, the eyeball contains lens, performing the functions of a lens. The main receptor apparatus of the eye is formed by the retina, which is the inner membrane of the eye.
The eye has its own assistive apparatus, which provides his movements and protection. Protective function perform structures such as eyebrows, eyelids, lacrimal sacs and ducts, eyelashes. The function of conducting impulses from the eyes to the subcortical nuclei of the cerebral hemispheres brain perform visual nerves having a complex structure. Through them, information from the visual analyzer is transmitted to the brain, where it is processed with the further formation of impulses going to the executive organs.
The function of the visual analyzer is vision, then it would be the ability to perceive light, size, mutual arrangement and the distance between objects using the organs of vision, which is a pair of eyes.
Each eye is contained in a socket (socket) of the skull and has an accessory eye apparatus and an eyeball.
The accessory apparatus of the eye provides protection and movement of the eyes and includes: eyebrows, upper and lower eyelids with eyelashes, lacrimal glands and motor muscles. The back of the eyeball is surrounded by fatty tissue, which acts as a soft elastic cushion. Above the upper edge of the eye sockets there are eyebrows, the hair of which protects the eyes from liquid (sweat, water) that can flow down the forehead.
The front of the eyeball is covered by the upper and lower eyelids, which protect the eye from the front and help moisturize it. Hair grows along the front edge of the eyelids, which forms eyelashes, the irritation of which causes the protective reflex of closing the eyelids (closing the eyes). The inner surface of the eyelids and the anterior part of the eyeball, with the exception of the cornea, are covered with conjunctiva (mucous membrane). In the upper lateral (outer) edge of each eye socket there is a lacrimal gland, which secretes a fluid that protects the eye from drying out and ensures the cleanliness of the sclera and the transparency of the cornea. The uniform distribution of tear fluid on the surface of the eye is facilitated by blinking of the eyelids. Each eyeball is moved by six muscles, of which four are called rectus muscles and two are called oblique muscles. The eye protection system also includes the corneal (touching the cornea or a speck entering the eye) and pupillary locking reflexes.
The eye or eyeball has a spherical shape with a diameter of up to 24 mm and a weight of up to 7-8 g.
Hearing analyzer- a set of somatic, receptor and nervous structures, the activity of which ensures the perception of sound vibrations by humans and animals. S. a. consists of the outer, middle and inner ear, auditory nerve, subcortical relay centers and cortical sections.
The ear is an amplifier and transducer of sound vibrations. Through the eardrum, which is an elastic membrane, and the system of transmitting ossicles - the malleus, incus and stapes - sound wave reaches the inner ear, causing oscillatory movements in the fluid filling it.
The structure of the hearing organ.
Like any other analyzer, the auditory one also consists of three parts: the auditory receptor, hearing ova nerve with its pathways and the auditory zone of the cerebral cortex, where the analysis and evaluation of sound stimulation occurs.
The organ of hearing is divided into the outer, middle and inner ear (Fig. 106).
The outer ear consists of the pinna and the external auditory canal. The skin-covered ears are made of cartilage. They capture sounds and direct them into the ear canal. It is covered with skin and consists of an outer cartilaginous part and an inner bone part. Deep in the ear canal are hair and skin glands that secrete a sticky yellow substance called earwax. It traps dust and destroys microorganisms. The inner end of the external auditory canal is covered by the eardrum, which converts airborne sound waves into mechanical vibrations.
The middle ear is a cavity filled with air. It contains three auditory ossicles. One of them, the malleus, rests on the eardrum, the second, the stapes, rests on the membrane of the oval window, which leads to the inner ear. The third bone, the anvil, is located between them. The result is a system of bone levers that increases the force of vibration of the eardrum by approximately 20 times.
The middle ear cavity communicates with the pharyngeal cavity using the auditory tube. When swallowing, the entrance to auditory tube opens, and the air pressure in the middle ear becomes equal to atmospheric pressure. Thereby eardrum does not bend in the direction where the pressure is less.
The inner ear is separated from the middle ear by a bone plate with two openings - oval and round. They are also covered with membranes. The inner ear is a bony labyrinth consisting of a system of cavities and tubules located deep in the temporal bone. Inside this labyrinth, as if in a case, there is a membranous labyrinth. It has two different organs: organ of hearing and organ balance -vestibular apparatus . All cavities of the labyrinth are filled with liquid.
The hearing organ is located in the cochlea. Its spirally twisted channel bends around the horizontal axis in 2.5-2.75 turns. It is divided by longitudinal partitions into upper, middle and lower parts. The hearing receptors are located in the spiral organ located in the middle part of the canal. The liquid filling it is isolated from the rest: vibrations are transmitted through thin membranes.
Longitudinal vibrations of air carrying sound cause mechanical vibrations of the eardrum. With the help of the auditory ossicles, it is transmitted to the membrane of the oval window, and through it to the fluid of the inner ear (Fig. 107). These vibrations cause irritation of the receptors of the spiral organ (Fig. 108), the resulting excitations enter the auditory zone of the cerebral cortex and here they are formed into auditory sensations. Each hemisphere receives information from both ears, making it possible to determine the source of sound and its direction. If the sounding object is on the left, then impulses from the left ear come to the brain earlier than from the right. This small difference in time allows not only to determine the direction, but also to perceive sound sources from different parts of space. This sound is called surround or stereophonic.
Understanding the analyzer
Represented by the perceptive department - the receptors of the retina of the eye, the optic nerves, the conduction system and the corresponding areas of the cortex in the occipital lobes of the brain.
A person sees not with his eyes, but through the eyes, from where information is transmitted through the optic nerve, chiasm, visual tracts to certain areas of the occipital lobes of the cerebral cortex, where that picture is formed outside world which we see. All these organs make up our visual analyzer or visual system.
Having two eyes allows us to make our vision stereoscopic (that is, form a three-dimensional image). The right side of the retina of each eye transmits through the optic nerve" right side" images in right side brain, acts similarly left-hand side retina. Then the brain connects two parts of the image - right and left - together.
Since each eye perceives “its own” picture, if the joint movement of the right and left eyes is disrupted, binocular vision may be disrupted. Simply put, you will begin to see double or see two completely different pictures at the same time.
Structure of the eye
The eye can be called a complex optical device. Its main task is to “transmit” the correct image to the optic nerve.
Main functions of the eye:
· optical system that projects the image;
· a system that perceives and “encodes” the received information for the brain;
· “servicing” life support system.
The cornea is the transparent membrane that covers the front of the eye. It lacks blood vessels and has great refractive power. Part of the optical system of the eye. The cornea borders the opaque outer layer of the eye - the sclera.
The anterior chamber of the eye is the space between the cornea and the iris. It is filled with intraocular fluid.
The iris is shaped like a circle with a hole inside (the pupil). The iris consists of muscles that, when contracted and relaxed, change the size of the pupil. It enters the choroid of the eye. The iris is responsible for the color of the eyes (if it is blue, it means there are few pigment cells in it, if it is brown, it means a lot). Performs the same function as the aperture in a camera, regulating the light flow.
The pupil is a hole in the iris. Its size usually depends on the light level. The more light, the smaller the pupil.
The lens is the “natural lens” of the eye. It is transparent, elastic - it can change its shape, almost instantly “focusing”, due to which a person sees well both near and far. Located in the capsule, held in place by the ciliary band. The lens, like the cornea, is included in optical system eyes.
The vitreous is a gel-like transparent substance located in the back of the eye. The vitreous body maintains the shape of the eyeball and is involved in intraocular metabolism. Part of the optical system of the eye.
Retina - consists of photoreceptors (they are sensitive to light) and nerve cells. Receptor cells located in the retina are divided into two types: cones and rods. In these cells, which produce the enzyme rhodopsin, the energy of light (photons) is converted into electrical energy of the nervous tissue, i.e. photochemical reaction.
The rods are highly photosensitivity and allow you to see in poor lighting; they are also responsible for peripheral vision. Cones, on the contrary, require more light for their work, but they allow you to see small details (responsible for central vision) and make it possible to distinguish colors. The largest concentration of cones is located in the central fossa (macula), which is responsible for the highest visual acuity. The retina is adjacent to the choroid, but in many areas it is loose. This is where it tends to flake off when various diseases retina.
The sclera is the opaque outer layer of the eyeball that merges at the front of the eyeball into the transparent cornea. 6 extraocular muscles are attached to the sclera. It contains a small number of nerve endings and blood vessels.
The choroid - lines the posterior part of the sclera; the retina is adjacent to it, with which it is closely connected. The choroid is responsible for the blood supply to intraocular structures. In diseases of the retina, it is very often involved in the pathological process. There are no nerve endings in the choroid, so when it is diseased, there is no pain, which usually signals some kind of problem.
Optic nerve - with the help of the optic nerve, signals from nerve endings are transmitted to the brain.
