Subject: Auditory analyzer. Organs of balance, smell and taste

Sense organs. Sensory systems.

visual sensory system. Organ of hearing and balance. Analyzers of smell and taste. Skin sensory system.

The human body as a whole is a unity of functions and forms. Regulation of the body's life support, mechanisms for maintaining homeostasis.

Topic for self-study: The structure of the eye. Ear structure. The structure of the tongue and the location of the zones of sensitivity on it. The structure of the nose. Tactile sensitivity.

Sense organs (analyzers)

A person perceives the world around him through the sense organs (analyzers): touch, sight, hearing, taste and smell. Each of them has specific receptors that perceive a certain type of irritation.

Analyzer (sense organ)- consists of 3 departments: peripheral, conductor and central. Peripheral (perceiving) link analyzer - receptors. They convert the signals of the outside world (light, sound, temperature, smell, etc.) into nerve impulses. Depending on the mode of interaction of the receptor with the stimulus, there are contact(skin receptors, taste receptors) and distant(visual, auditory, olfactory) receptors. conductor link analyzer - nerve fibers. They conduct excitation from the receptor to the cortex hemispheres. Central (processing) link analyzer - a section of the cerebral cortex. Violation of the functions of one of the parts causes a violation of the functions of the entire analyzer.

There are visual, auditory, olfactory, gustatory and skin analyzers, as well as a motor analyzer and a vestibular analyzer. Each receptor is adapted to its specific stimulus and does not perceive others. Receptors are able to adapt to the strength of the stimulus by reducing or increasing sensitivity. This ability is called adaptation.

visual analyzer. Receptors are excited by light quanta. The organ of vision is the eye. It consists of eyeball and ancillary apparatus. Auxiliary device represented by eyelids, eyelashes, lacrimal glands and muscles of the eyeball. Eyelids formed by folds of skin lined from the inside with a mucous membrane (conjunctiva). Eyelashes protect the eye from dust particles. Lacrimal glands located in the outer upper corner of the eye and produce tears that wash the anterior part of the eyeball and enter the nasal cavity through the nasolacrimal canal. Muscles of the eyeball set it in motion and orient it towards the object in question.

Eyeball located in the orbit and has a spherical shape. It contains three shells: fibrous(outer), vascular(middle) and mesh(internal) and inner core, consisting of lens, vitreous body and aqueous humor anterior and posterior chambers of the eye.

The posterior part of the fibrous membrane is a dense opaque connective tissue albuginea (sclera), front - transparent convex cornea. The choroid is rich in vessels and pigments. It distinguishes actually choroid(rear end), ciliary body and rainbow shell. The main mass of the ciliary body is the ciliary muscle, which changes the curvature of the lens with its contraction. Iris ( iris) has the form of a ring, the color of which depends on the amount and nature of the pigment it contains. There is a hole in the center of the iris pupil. It can narrow and expand due to the contraction of the muscles located in the iris.

The retina is divided into two parts: back- visual, perceiving light stimuli, and anterior- blind, not containing photosensitive elements. The visual part of the retina contains light-sensitive receptors. There are two types of visual receptors: rods (130 million) and cones (7 million). sticks are excited by weak twilight light and are not able to distinguish color. cones excited by bright light and able to distinguish color. The sticks contain red pigment - rhodopsin, and in cones - iodopsin. Directly opposite the pupil there is yellow spot - the place of best vision, which consists only of cones. Therefore, we see objects most clearly when the image falls on yellow spot. Toward the periphery of the retina, the number of cones decreases, the number of rods increases. On the periphery are only sticks. The place on the retina where the optic nerve exits is devoid of receptors and is called blind spot.

Most of the cavity of the eyeball is filled with a transparent gelatinous mass, forming vitreous, which maintains the shape of the eyeball. lens is a biconvex lens. Its back is adjacent to the vitreous body, and the front is facing the iris. With the contraction of the muscle of the ciliary body associated with the lens, its curvature changes and the rays of light are refracted so that the image of the object of vision falls on the yellow spot of the retina. The ability of the lens to change its curvature depending on the distance of objects is called accommodation. If accommodation is disturbed, there may be myopia(the image is focused in front of the retina) and farsightedness(the image is focused behind the retina). With myopia, a person sees indistinctly distant objects, with farsightedness, near ones. With age, the lens thickens, accommodation deteriorates, and farsightedness develops.

On the retina, the image is inverted and reduced. Thanks to the processing in the cortex of information received from the retina and receptors of other sense organs, we perceive objects in their natural position.

auditory analyzer. The receptors are excited by sound vibrations in the air. The organ of hearing is the ear. It consists of the outer, middle and inner ear. outer ear consists of the auricle and ear canal. auricles are used to capture and determine the direction of sound. External auditory canal begins with the external auditory opening and ends blindly tympanic membrane which separates the outer ear from the middle ear. It is lined with skin and has glands that secrete earwax.

Middle ear It consists of the tympanic cavity, the auditory ossicles and the auditory (Eustachian) tube. tympanic cavity filled with air and connected to the nasopharynx by a narrow passage - auditory tube, through which the same pressure is maintained in the middle ear and the space surrounding the person. auditory ossicles - hammer, anvil and stirrup - connected to each other movably. According to them, fluctuations from eardrum transmitted to the inner ear.

inner ear consists of a bony labyrinth and a membranous labyrinth located in it. Bone labyrinth contains three sections: vestibule, cochlea and semicircular canals. The cochlea belongs to the organ of hearing, the vestibule and semicircular canals - to the organ of balance (vestibular apparatus). Snail- bone canal, twisted in the form of a spiral. Its cavity is divided by a thin membranous septum - the main membrane on which receptor cells are located. The vibration of the cochlear fluid irritates the auditory receptors.

The human ear perceives sounds with a frequency of 16 to 20,000 Hz. sound waves They reach the tympanic membrane through the external auditory canal and cause it to vibrate. These vibrations are amplified (almost 50 times) by the auditory ossicles and are transmitted to the fluid in the cochlea, where they are perceived by the auditory receptors. The nerve impulse is transmitted from the auditory receptors through the auditory nerve to the auditory zone of the cerebral cortex.

vestibular analyzer. vestibular apparatus located in the inner ear and represented by the vestibule and semicircular canals. threshold consists of two bags. Three semicircular canals located in three mutually opposite directions corresponding to the three dimensions of space. Inside the sacs and channels there are receptors that are able to perceive fluid pressure. The semicircular canals receive information about the position of the body in space. The sacs perceive deceleration and acceleration, changes in gravity.

Excitation of the receptors of the vestibular apparatus is accompanied by a number of reflex reactions: a change in muscle tone, muscle contraction, contributing to the straightening of the body and maintaining the posture. Impulses from the receptors of the vestibular apparatus through the vestibular nerve enter the central nervous system. Vestibular analyzer functionally connected with the cerebellum, which regulates its activity.

Taste analyzer. Taste buds are irritated chemicals, dissolved in water. The organs of perception are taste buds- microscopic formations in the mucous membrane of the oral cavity (on the tongue, soft palate, posterior pharyngeal wall and epiglottis). Receptors specific to the perception of sweet are located on the tip of the tongue, bitter - on the root, sour and salty - on the sides of the tongue. With the help of taste buds, food is tested, its suitability or unsuitability for the body is determined, when they are irritated, saliva and gastric and pancreatic juices are released. The nerve impulse is transmitted from the taste buds through the taste nerve to the taste zone of the cerebral cortex.

Olfactory analyzer. The olfactory receptors are irritated by gaseous chemicals. The organ of perception is the perceptive cells in the nasal mucosa. Nerve impulses are transmitted from olfactory receptors through olfactory nerve in the olfactory cortex of the cerebral hemispheres.

Skin analyzer. The skin contains receptors , perceiving tactile (touch, pressure), temperature (thermal and cold) and pain stimuli. The organs of perception are the perceiving cells in the mucous membranes and skin. The nerve impulse is transmitted from the tactile receptors through the nerves to the cerebral cortex. With the help of tactile receptors, a person gets an idea of the shape, density, temperature of bodies. Tactile receptors are most found on the fingertips, palms, soles of the feet, and tongue.

motor analyzer. Receptors are excited during contraction and relaxation muscle fibers. The organs of perception are the perceiving cells in the muscles, ligaments, on the articular surfaces of the bones.

The skin forms the outer covering of the body. Skin area 1.5-1.6 m 2 , thickness - from 0.5 to 3-4 mm.

Skin functions: protective (against harmful effects and penetration of microorganisms); thermoregulation (through the blood vessels of the skin, sweat glands, subcutaneous fatty tissue: a person loses 85-90% of the heat generated in him through the skin); excretory (due to the sweat glands: as part of sweat, water is removed through the skin, mineral salts and some organic compounds); receptor (in the skin are pain, temperature, tactile receptors); blood depot (up to 1 liter of blood is deposited in the vessels of the skin); vitamin metabolism (the skin contains a precursor of vitamin D, which is converted to vitamin D under the influence of ultraviolet rays).

The skin is made up of epidermis and the actual skin dermis. The subcutaneous tissue is adjacent to the dermis adipose tissue. Skin derivatives are hair, nails, sebaceous, sweat and mammary glands.

Epidermis It is represented by stratified squamous keratinized epithelium, in which five layers are distinguished. The deepest of them - basal layer. It is formed by basal skin cells capable of dividing, due to which all layers of the epidermis are renewed, and by pigment cells containing pigment - melanin, which protects the human body from ultraviolet rays. Most surface layer - horny- consists of keratinized cells and is completely renewed in 7-11 days.

Dermis (actual skin) It has two layers: papillary and reticular. papillary layer composed of loose connective tissue. It depends on the pattern of the skin. The papillary layer contains smooth muscle cells, blood and lymphatic vessels, and nerve endings. mesh layer formed by dense connective tissue. Bundles of collagen and elastic fibers form a network and give the skin strength. This layer contains sweat and sebaceous glands and hair roots.

Behind the dermis is the subcutaneous layer fatty tissue. It consists of loose connective tissue containing fatty deposits.

sweat glands concentrated on the border of the reticular layer and subcutaneous adipose tissue. The excretory ducts open on the surface of the skin with pores. Sweat glands are rich in the skin of the palms, soles of the feet, and armpits. During sweating, heat transfer and removal of metabolic products occur. With sweat, water (98%), salts, uric acid, ammonia, urea, etc.

Sebaceous glands located in the reticular layer, on the border with the papillary. Their excretory ducts open into the hair follicle. The secret of the sebaceous glands is sebum, which lubricates the hair and softens the skin, while maintaining its elasticity.

Hair consists of a root and a stem. Root the hair has an extension - the hair follicle, into which the hair papilla protrudes from below with blood vessels and nerves. Hair grows by cell division hair bulb. The hair root is surrounded by a hair follicle, to which the smooth muscle that lifts the hair is attached. At the point of transition of the hair into the shaft, a recess is formed - a hair funnel, into which the ducts of the sebaceous glands open. Kernel consists of keratinized cells containing air bubbles and melanin granules. By old age, the amount of pigment in keratinized cells decreases and the number of gas bubbles increases - the hair turns gray.

Nails- horny plates on the back surface of the terminal phalanges. The nail lies in a bed of germinal epithelium and connective tissue. The skin of the nail bed is rich blood vessels and nerve endings.

Hardening of the body. Hardening improves immunity. Sun, air and water are the best natural hardening factors. They increase the body's resistance to adverse environmental conditions, various colds and infectious diseases. Basic requirements for hardening: 1) gradualness; 2) systematic; 3) a variety of means of hardening.

The mechanism of excitation of taste receptor cells

The interaction of taste cells with molecules of stimulating substances occurs at the level of the microvilli membrane. Stimulating substances interact with the chemoreceptor substance, conformational changes occur, leading to the opening of Na + channels and depolarization of the microvilli membrane of receptor cells. As a result, a receptor potential arises, which causes the release of the mediator from the receptor cell and the action of the mediator on the endings of sensory nerves. In the latter, under the influence of a mediator, a GP arises, which, upon reaching the KRD, turns into PD.

Wire and cork sections of the taste sensory system

From the anterior two-thirds of the tongue departs lingual nerve(n. Lingualis), which is later attached to the drum string (p. Chorda tympani) and facial nerve(n.facialis). body first neuron located in the crankshaft (v. Depikiii), from there, impulses are sent along the facial nerve to the medulla oblongata, namely to the nucleus lonely way(n. tr. solitarius). From the posterior third of the tongue, impulses are received by the fibers of the glossopharyngeal nerve (n. glossopharyngeus) to the body of the first neuron located in rocky knot(d. petrosus). From there the impulses are conducted to the core of the lonely path. Further, after a partial intersection, the paths pass into the bodies the third neuron laid down in posteroventral medial nucleus of the thalamus for taste reception and postero-ventral lateral nucleus - for temperature and tactile sensitivity.

From the thalamus, impulses are conducted to postcentral gyrus(d. Postcentralis) in the projection of the tongue (Fig. 12.31).

Part of the impulses enters the opercular cortex of the temporal lobe and parahypocampal gyrus, hypothalamus, amygdala. These connections provide information to the limbic system.

Rice. 12.30. The structure of the taste buds and the ultrastructure of the taste bud:

A - fungiform papilla, B - foliate papilla, C - grooved papilla.

1 - taste fossa, 2 - microvillus apparatus, 3 - pigment granule, 4 - mitochondria, 5 - supporting cell, 6 - receptor cell, 7 - nerve endings, 8 - basal membrane, 9 - basal cell

Rice. 12.31. Taste pathway diagram:

V - lingual nerve, VII - facial nerve, IX- glossopharyngeal nerve

Thresholds of taste sensation

Taste thresholds are divided into two types:

1. Thresholds of gustatory sensation, that is, the minimum gustatory irritation that can cause a sense of taste.

2. Thresholds of discrimination - as a minimum taste irritation, capable of providing recognition of a taste sensation.

It is clear that the first below others. At different people they are different. Thresholds depend on the state of the body (hunger, pregnancy, age, etc.). The greatest sensitivity of taste buds is observed on an empty stomach. After eating, the excitability of receptors decreases due to reflex action from the gastric mucosa when irritated by food lumps. it gastrolingual reflex. Taste buds in this case play the role of effectors.

Taste thresholds are rising in the elderly. They also depend on the surface of irritation: with a smaller surface, they increase, and vice versa. The threshold values also depend on the flavoring substance. The lowest thresholds for bitter substances. This is understandable, since it is among the bitter substances that poisons are most often found, so it is important to distinguish them at a lower concentration. The thresholds for sweet and salty are almost the same.

The nature of taste sensations is influenced not only by olfactory, but also by temperature and tactile stimuli. The optimal limits for taste sensitivity are in the range from 20 to 38 ° C.

Adaptation of the taste system

If the gustatory substance acts long enough, adaptation to it occurs, that is, the thresholds grow, and the sensitivity decreases. The degree of adaptation depends on the concentration of the flavoring substance. The slowest adaptation to bitter and sour, the fastest - to sweet and salty. When adapting to one substance, sensitivity to the action of other substances may change. For example, adaptation to bitterness leads to a decrease in sensitivity to sour and salty foods.

The cerebral cortex constantly receives and analyzes various information coming from internal organs and from the external environment. The perception and analysis of this information is provided by analyzers - derivatives of the nervous system.

Analyzer- it is one functional system neurons that perceive irritation, transmit excitation and analyze it in the cerebral cortex. In each analyzer, according to I.P. Pavlov distinguishes three departments: perceiving, conducting and central.

1) Receiving Department are receptors that transform the energy of external or internal irritation into the nervous process. They are divided into two groups: exteroreceptors, which perceive irritations from the external environment and, together with auxiliary structures, form sense organs, and interoreceptors which perceive irritations from the internal environment of the body. These include visceroreceptor s(located in internal organs and perceive various sensations, for example, the fullness of the filling of the stomach, intestines, bladder, pain); proprioreceptors(located in the musculoskeletal system and cause a muscular-articular feeling); vestibuloreceptors(located in the locomotor apparatus and the organ of balance - they signal a change in the position of the body and its individual parts in space.

2) Conducting department serves to carry out nervous irritation. It includes nerves (spinal and cranial) and exteroceptive pathways of the spinal cord and brain.

3) Central department- these are neurons of the projection zones of the cerebral cortex (visual, auditory, etc.), where the analysis and synthesis of the received sensations takes place. On the basis of the incoming information, the attitude to the surrounding world and the body's response to stimuli in various situations are formed.

Classification of analyzers.

Depending on which stimulus the receptors perceive, the following analyzers are distinguished:

1) Visceral Analyzers perceive irritations that occur in organs and tissues, and signal to the central nervous system about the state internal environment organism. Receptive department - interoreceptors, conductive - spinal and cranial nerves, central - brain and spinal cord.

2) Tactile Analyzer perceives various irritations from the external environment (cold, heat, touch, pressure, pain ...). Perceiving department - exteroreceptors of the skin and mucous membranes of a number of organs in contact with external environment, namely the mucous membranes of the eyes, lips, mouth, tongue, nasal cavity, rectum and external genital organs. The receptive region is sometimes also called organ of touch(organon tactus). Skin sensitivity is due to nerve endings that have a different shape and structure. Various sensitive points and areas of the skin can be considered as projections of the corresponding points of the brain. The following areas of the skin are especially rich in sensitive nerve endings: lips, tip of the nose, trunk or proboscis (pig, mole), fingertips (primates). In addition to the skin itself, the hair associated with the nerve endings also has a sense of touch. In a number of places, special tactile hairs (vibrissae) develop. They are especially common on the lips and cheeks and in the form of separate tufts above the eyes and on the chin, forming a sensitive area on the muzzle. The conducting department of the tactile analyzer - s / m and cranial nerves, central department- spinal cord and brain.

3) Taste Analyzer provides analysis of the received feed and water. In animals, it has not been studied enough yet, but there is evidence that they can distinguish all four basic tastes (sweet, bitter, sour and salty), but prefer certain taste sensations. So, pigs and dogs prefer sweet, large cattle and horses are salty. As for birds, their sense of taste is poorly developed and largely replaced by touch. Perceiving department of the taste analyzer, or organ of taste(organon gustus) is represented by numerous taste buds, which are located in the epithelial cover of the oral mucosa.

In domestic animals, taste buds sit mainly on taste buds. In addition to them, they are also found in the pharynx, hard and soft palate, pharynx, and larynx. In young animals, they are more common and can occur in other places of the oropharynx, and in adults - on the tip, edges and back of the tongue. The largest number taste buds have animals with well-developed chewing surfaces of molars (horse, cow, sheep, goat) - several tens of thousands. In humans, the total number of taste buds reaches two thousand. Taste buds, located in the thickness of the mucous membrane, form its numerous outgrowths - papillae. The papillae of the tongue are heterogeneous in their function and are divided into mechanical and gustatory. Taste buds include: mushroom-shaped, leaf-shaped, roller-shaped. AT fungiform papillae taste buds are usually concentrated in its expanded top (hat) - they perceive sour and salty taste.

Foliate papillae are vertically oriented folds. Taste buds lie on the sides of these folds facing each other. They perceive the sweet taste.

Valid (grooved) papillae have the form of a cylinder surrounded by a roller. Taste buds are located both on the side surfaces of the cylinder and on the inside. They perceive bitter taste. In a hungry animal or human, the taste buds are in a state of high activity. While eating, their activity noticeably decreases and begins to gradually recover only after one and a half to two hours. And only four to five hours after eating, the ability to acutely perceive taste stimuli again becomes high. If you eat the same food day after day, it starts to seem tasteless. This is due to the habituation of taste buds to monotonous irritations. Various spices and seasonings for dishes increase their sensitivity.

To a certain extent, products that contrast in taste, such as sweet tea and a sandwich with salted fish, excite and restore the activity of taste receptor cells. At various diseases organs of the gastrointestinal tract, taste sensitivity is distorted, even the appearance of the tongue changes. So, according to the observations of clinicians, in chronic gastritis with high acidity, chronic enteritis, colitis, the tongue slightly increases in volume and is almost completely covered with a whitish coating. A dry, coated and slightly reduced in size tongue is characteristic of gastritis with low and zero acidity. With an exacerbation peptic ulcer plaque is often gray or yellowish-gray. With the help of this plaque, the body, as it were, seeks to block the taste apparatus of the tongue, thereby suppressing appetite and creating a sparing regimen for the diseased organ. Particular attention is paid to plaque in the language. So, a thin coating indicates an incipient disease or superficial localization. pathological process; significantly more pronounced plaque is a sign chronic illness. If a white coating on the tongue, gradually thickening, becomes yellow, and then gray, dark in color, this means the progression of the disease. Lightening, thinning of plaque indicates an improvement in the condition.

So, sensory part of the taste analyzer represented by taste buds. Each taste bud is formed by taste receptor and supporting cells. The shape of the kidney resembles an onion, the top of which is turned towards the surface of the tongue and opens on it with a tiny opening - the taste pore. Microvilli of receptor cells face into the lumen of the taste pore; they, in fact, come into direct contact with various nutrients. As soon as this happens, reactions begin in the receptor cell, as a result of which the chemical irritation is transformed into a nerve impulse. Information about the food substance goes along the nerve fibers (there are several of them for each taste bud), which are combined into nerves.

Conducting department represented by cranial nerves: tympanic string (7th facial nerve) - from the anterior 2/3 of the tongue; glossopharyngeal nerve (9th) - from the posterior 1/3 of the tongue and from the roller-shaped papillae; vagus nerve (10th) - from the pharynx. The central processes of neurons that carry out gustatory innervation in the oral cavity are sent to the above-mentioned nerves to the sensory nucleus common to them, which lies in the medulla oblongata. The axons of the cells of this nucleus are sent to the thalamus (interbrain), where the impulse is transmitted to the following neurons, the central processes of which end in the cerebral cortex .. So, taste center The brain is located in the temporal lobe. This is where the highest analysis of taste sensations takes place.

4) Olfactory analyzer provides the ability to distinguish odors. In the life of land animals, the sense of smell plays important role in communication with the external environment. It serves to recognize odors, to determine the gaseous substances contained in the air. In the process of evolution, the olfactory organ, which is of ectodermal origin, first formed near the mouth opening, and then combined with the initial section of the upper respiratory tract, which separated from oral cavity. In some mammals, the sense of smell is very well developed (macromatics). This group includes insectivorous, ruminant, ungulates, carnivores. Other animals have no sense of smell at all (anosmatics). Dolphins are among them. The third group of animals has a sense of smell, but it is poorly developed (microsmatics).

These include pinnipeds and primates. The olfactory analyzer belongs to remote action devices and consists of a perceiving (receptor) apparatus, pathways and a part of the brain where higher analysis and synthesis of odor information. The perceiving apparatus of the analyzer is located in the initial section of the airways - in the olfactory part of the nasal cavity. This is a relatively small area, the mucous membrane stands out here with its swelling and color of the pigment, for example, in cereals. and small horn. cattle, a horse - yellow, a pig - brown, a dog and a cat - gray color. In animals with a highly developed sense of smell (dogs), it can be folded. In this place, in the thickness of the mucous membrane, olfactory neurosensory cells lie, alternating with supporting (supporting), they fit snugly enough to each other, forming an olfactory epithelium. The receptor layer of the olfactory lining is not continuous; it is interrupted in the depth of the folds. Here, scattered small olfactory (Bowman's) glands open, secreting a secret that also contains mucus, which protects the mucous membrane from drying out and dissolves odorous substances and thus makes them available for receptor perception. The process of smell perception begins with the olfactory receptor cell. Their number can reach 200 million in a dog, 100 million in a rabbit, 80 million in ungulates, and 40 million in humans.

In shape, the olfactory cells resemble a spindle with two processes: one is short, peripheral, goes to the surface of the mucous membrane, the other is long, central - to the brain. The peripheral processes have a thickening at the end in the form of a club with 10-12 thin hairs - cilia. These cilia are extremely mobile: they bend, straighten, turn in different sides, as if looking for and capturing the molecules of odorous substances. On the olfactory cilia, receptor sites were found that are distinguished by a special structure and properties, due to which they come into contact only with certain odorous molecules. As a result of such contact, a nerve impulse is born in the receptor cell, which goes through the central process to the brain. The central processes form 15-20 olfactory nerves. The olfactory nerves through the holes of the perforated plate of the ethmoid bone penetrate the cranial cavity, reaching the next section of the olfactory analyzer - the olfactory bulbs. The olfactory bulb is a complexly organized center where all information about the smell is pre-processed. From the bulbs, along two olfactory tracts, through the olfactory triangles, signals enter the pear-shaped lobes (secondary olfactory centers), the hippocampus (higher subcortical olfactory centers) and the temporal cortex of the brain, where the higher part of the olfactory brain is located and where, after final processing and synthesis of information a sense of smell is formed.

5) visual analyzer perceives the size, shape, color of objects of the external world, their location in space, movement, etc. Receiving Department visual analyzer is the organ of vision (organon visus), which consists of the eye and protective auxiliary devices (orbit, periorbita, conjunctiva, eyelids, lacrimal apparatus and eye muscles).

The eye or eyeball is a paired optical organ of a spherical shape. Nocturnal animals have the largest eyeball. Among domestic animals, cats have the largest eyes in relation to body size, then dogs. In underground animals, due to the reduction of the organs of vision, the eyeballs are very small and almost completely hidden under the skin (mole, shrew). The visual axes located in the orbits of the eyes also have a different direction in animals. When the visual axes of both eyes approach, i.e. As the angle between them decreases, the field of view of one eye overlaps the field of view of the other eye. This achieves a quality binocular vision. With more primitive monocular vision, both fields of vision are independent of each other, and as a result, the field of vision is much larger, but of less quality. The angle of view (between both visual axes) is: for a hare - 170 o, for a horse - 137 o, for a pig - 118 o, for a dog - 93 o, for a cat -77 o, for a person - 14 o, for a lion - 10 about. These values are determined by the lifestyle of animals - some need a large field of view in order to escape in time (hare, horse), while others, on the contrary, need the quality of vision for accurate orientation when catching prey (cat, lion).

The wall of the eyeball is formed by three shells. The outer (fibrous) membrane or sclera, which makes up 4/5 of the entire circumference of the eye, is the thickest, strongest; it provides the eyeball certain form and consists mainly of collagen fibers. Only in the anterior section is a tiny window, as it were, cut into the sclera - the cornea. On the border of the sclera and cornea there is a groove - limbus. The network of capillaries embedded in the limbus nourishes the cornea, which does not have its own blood vessels, which largely determines its absolute transparency. The choroid is adjacent to the outer shell, which consists of its own choroid, ciliary body and iris. The iris is located behind the cornea and contains cells - myopigmentocytes, which determine its color and can expand or narrow the pupil. The pupil is a small hole in the center of the iris. Its shape has specific differences: in dogs, pigs and primates it is round in shape, in a cat it is in the form of a vertical slot, in herbivores it is transversely oval. The iris is separated from the choroid itself by the ciliary or ciliary body. In its thickness there is a ciliary muscle, during the contraction of which the ligaments that hold the lens relax and it becomes more convex. And when the ciliary muscle relaxes, the ligaments, on the contrary, stretch, which leads to some flattening of the lens. Thus, the ciliary body provides focusing of vision, without which it is impossible to distinguish objects located at a distance. The inner layer of the ciliary body, rich in blood vessels, produces intraocular fluid that enters the chambers of the eye (anterior and posterior). Due to this fluid, the cornea, lens and vitreous body are nourished. The lens, vitreous body and intraocular fluid make up the optical or refractive system of the eye. Inside the choroid itself, herbivores and predators have a reflective zone (tapetum), which has a crescent shape and a blue-green color. Thanks to her, the eyes glow in the dark and have the ability to see in reflected light. The innermost of the three shells is the reticulum.

As the ancient Greek scholar wrote Herophilus“The retina is a tight fishing net thrown to the bottom of the eyecup and catching Sun rays". In the photoreceptor layer of the retina (and there are 10 layers in total) there are light-perceiving elements: highly specialized cells with processes in the form of rods and cones. Rods provide twilight vision, and cones are adapted to daylight and perceive colors. And rods are much more sensitive than cones. Thanks to them, we see quite well in the dark, but we do not distinguish colors: as you know, at night all cats are gray. The ability of the eye to perceive different colors is provided by three types of cones: red-, blue- and green-sensitive. Therefore, normal vision in humans is called three-dimensional, or trichromatic. As for colorblind people who cannot distinguish between red and green color, then they do not have green-sensitive or red-sensitive cones in the retina. Color vision is not expressed in all animals. The horse distinguishes red, green, yellow, blue and purple colors, the cow and the pig - red, yellow, green and blue colors. The dog well distinguishes up to 50 shades of gray from black to white, and there is evidence that dogs are able to distinguish green. As for birds, most of them have color vision. Cones and rods are connected through intermediate bipolar cells with large ganglion cells, which give rise to nerve fibers. Gathering in a bundle, these fibers form the optic nerve, which emerges from the eyeball and goes to the brain. Disk optic nerve- the exit site of the fibers is clearly visible when examining the fundus. There are no rods and cones here, so the light is not perceived by this part of the retina and the spot is called blind. And almost next to it is another oval-shaped spot called yellow. This is the place where vision is best, since the retina is thinnest in the area of the macula. Thus, the perceiving department of the visual analyzer is the retina; conductive - 2 pairs of cranial (optic) nerves and optic tracts; central - the lateral geniculate body (thalamus), the visual tubercles of the quadrigemina and the occipital lobes of the cerebral cortex.

6) Equilibrium auditory the analyzer is designed to perceive the sounds of the outside world and the position of the body in space. The greatest hearing acuity is observed in carnivorous animals (dog, cat), the average - in primates, and some animals are even able to perceive ultrasound ( the bats, whales, dolphins). The perceiving department of the statoacoustic analyzer is represented by the vestibulocochlear organ (organum vestibulocochleare). The organ of hearing and balance is divided into three parts: the outer ear, middle ear and inner ear. outer ear serves to capture sound vibrations and consists of the auricle, its muscles and the external auditory canal. The basis of the auricle is elastic cartilage, covered with skin. The external auditory canal is a canal that starts at the external auditory canal and ends at the tympanic membrane. In its wall lie sebaceous glands, as well as sulfuric, releasing earwax. In cattle and pigs, the external auditory meatus is long, while in horses and dogs it is short. The eardrum is made of dense connective tissue (collagen fibers) and separates the outer ear from the middle ear. It is absent in cetaceans.

Middle ear is a sound-conducting department and is located in the tympanic cavity, which is filled with air and connected to the pharynx through the auditory tubes. Through these pipes, the air pressure in the tympanic cavity is balanced with atmospheric pressure. The horse in the area of the auditory tube has a bag-like protrusion - an air sac with a capacity of 450 cm 3. In the middle ear there are 4 auditory ossicles (hammer, anvil, lenticular bone and stirrup), which are interconnected by joints and ligaments. The malleus is fused with the tympanic membrane. The vibrations of the membrane, arising under the action of sound waves, are transmitted to the malleus, from it to the anvil, then to the lenticular bone and from it to the stirrup. The base of the stirrup is movably inserted into an oval-shaped window “cut out” on the inner wall of the tympanic cavity. This wall separates tympanic cavity from the inner ear. Through the chain of these bones, sound vibrations, amplified 22 times, are transmitted from the tympanic membrane to the wall of the inner ear, behind which is located a specific fluid (perilymph), which is also capable of vibrating.

inner ear consists of a bony labyrinth and a membranous labyrinth located in it. Bone labyrinth is a system of bony hollow formations, which are located in the thickness of the temporal bone. It is divided into three parts: vestibule, semicircular canals and cochlea. membranous labyrinth approximately repeats the shape of the bone labyrinth and is a collection of interconnected cavities filled with fluid - endolymph. The soft walls of the membranous labyrinth are very sensitive to vibrations of the perilymph that surrounds them from the outside, and transmit them to the endolymph, which in turn also begins to vibrate. The membranous labyrinth is conditionally divided into two parts: auditory and vestibular.

auditory part represented by the membranous snail. The number of its curls (turns) depends on the type of animal, so there are 2 in a horse and a rabbit, 3 in cattle and a dog, 4 in a pig. . The main elements of the spiral organ are receptor cells that perceive sound stimuli. These cells are called hair cells (auditory) and they are located between the support cells. In receptor hair cells, the physical energy of sound vibrations is converted into nerve impulses. Sensory endings of the auditory (cochlear) nerve approach the hair cells, which perceive information about sound and transmit it further along the nerve fibers. The higher auditory center is located in the temporal lobe of the cerebral cortex: here the analysis and synthesis of sound signals is carried out.

vestibular part of the membranous labyrinth represented by the vestibule and semicircular membranous canals. On the threshold, oval and round sacs are distinguished. On the walls of the sacs and channels there are small elevations - maculae - sensitive spots and scallops that contain receptor hair and supporting cells. Above these crests and spots in the endolymph, calcite crystals float - otoliths, which form the otolith membrane. When this membrane is displaced, irritation of the receptor hair cells occurs and a nerve impulse is produced, which is transmitted further along the nerve fibers of the vestibular (vestibule) nerve. Together with the fibers of the cochlear nerve, the vestibular nerve forms the 8th pair cranial nerves- predverno-cochlear. Its fibers terminate in the vestibular nucleus of the Deiters medulla oblongata. The axons of the cells of this nucleus begin the central pathways of the vestibular analyzer, which reach the cerebellum and the cortex (temporal lobe) of the brain.

Phylogeny of the sense organs.

The sense organs are of ectodermal origin. In invertebrates, they are mainly represented by sensitive cells that are located in the epidermis and are associated with receptor nerve endings.

The lancelet has photosensitive cells (eyes of Hesse), an olfactory fossa, and sensory cells on the mouth tentacles.

In cyclostomes, paired organs of vision develop - the eyes, there is an olfactory capsule and a lateral line organ appears, which perceives the movement of water.

In fish, taste organs are formed in the oral and pharyngeal regions, there are olfactory pits, eyes develop (rods and cones appear in the retina and the lens) and the lateral line organ.

In amphibians, an organ of smell arises, and taste buds form taste buds, an organ of hearing appears, and a lateral line organ gives rise to the inner ear.

In reptiles, nasal conchas appear, where the organ of smell is located; cones develop in the retina of the eye, the lens can change the curvature; the organ of hearing and balance is formed.

In birds and mammals, the sense organs reach their greatest development.

The olfactory analyzer is phylogenetically the most ancient sense organ and is present in very many organisms at different stages of their evolutionary development. With the help of the olfactory analyzer, animals adapt to environment- they look for food, water, escape from predators during the mating season, find animals of the opposite sex for reproduction. Many animals use their scents to mark their territory. Smell substances are distributed with the air over long distances from their source and they are captured by other animals.

Especially great signal value are odorous substances released by animals and insects into the environment - pheramones. These odors serve as a means of communication between animals of the same species.

In some animals, the sense of smell is relatively poorly developed - these are the so-called microsmatics (birds, monkeys, humans). In the other majority of animals, it is well developed (macromatics). So in dogs there are from 100 to 200 million, and in humans only 10-60 million olfactory cells. The olfactory epithelium is located away from the main respiratory tract and the inhaled air enters there by vortex movements or diffusion. Such whirling movements occur during "sniffing", i.e. with short breaths through the nose and expansion of the nostrils, which facilitates the penetration of the analyzed air into these areas.

Olfactory cells are represented by bipolar neurons, the axons of which form the olfactory nerve, ending in the olfactory bulb, which is the olfactory center, and then paths go from it to other overlying brain structures. On the surface of olfactory cells there is a large number of cilia, significantly increasing the olfactory surface. The intensity of the olfactory sensation depends on chemical structure and the concentration of an odorous substance in the air, from a series external factors(temperature, air humidity) and the functional state of the olfactory epithelium. With a cold, olfactory sensitivity decreases. Maximum olfactory sensitivity is reduced. The maximum olfactory sensitivity is felt only at the first moment of the action of the odorous substance. Then the adaptation of the receptors develops very quickly and the body ceases to smell. At the same time, adaptation occurs more slowly if the air is rhythmically intermittently inhaled and exhaled, because. excitation of receptors occurs only when air moves at the moment of inhalation, and when exhaling, air does not enter the olfactory zone. It is possible to adapt to one odor while maintaining sensitivity to other odors, so it is assumed that substances with different odors act on different receptors. However, there are other explanations, so the question of the mechanism of the emergence of smell requires further clarification.

The acuity of smell is determined by the threshold of sensation, i.e. the minimum amount an odorous substance that can cause the sensation of smell.

Taste analyzer serves to determine the character, palatability feed, its suitability for eating. Taste and olfactory analyzers help animals living in water to navigate in the environment, determine the presence of food, females. With the transition to life in air environment the value of the taste analyzer decreases. In herbivorous animals, the taste analyzer is well developed, which can be seen in the pasture and in the feeder, when the animals do not eat grass and hay all in a row.

The peripheral part of the taste analyzer is represented by taste buds located on the tongue, soft palate, back wall pharynx, tonsils and epiglottis. Taste buds are located on the surface of fungiform, foliate and trough papillae.

The bulb consists of supporting and 2-6 receptor cells with microcilia on their surface. The narrowed part of the bulb has a small hole - a taste pore through which the dissolved substance penetrates, acting on taste buds. Most of the receptors are at the tip, edges and back of the tongue.

In the mucous membrane of the tongue and other parts of the oral cavity there are receptors that perceive temperature, touch, pressure, pain. And what we call taste is the result of irritation not only of taste, but also of a number of other listed v.ch. olfactory, visual, and other receptors. Therefore, the taste of the same warm or cold, liquid or thicker product is perceived differently. A temporary loss of smell is also observed with a runny nose, which leads to a violation of taste sensations.

There are four main taste sensations- bitter, sweet, sour and salty.

The sensation of sweet is more perceived by the anterior part of the tongue, bitter by its base, sour by the middle part of its lateral surface, salty by the tip and lateral edge.

Ruminants, horses, pigs distinguish all four tastes well. However, pigs prefer sweet, cattle and horses prefer salty.

The sensitivity of the taste analyzer is largely determined by the degree of the animal's need for food, the functional state of the digestive organs and other body systems, the usefulness and set of feed in the diet.

Afferent taste fibers are part of the facial, glossopharyngeal and vagus nerve in medulla, further into the thalamus and into the cortical zone of the taste analyzer.

41. Taste analyzer- neurophysiological system, the work of which provides an analysis of chemicals entering the oral cavity. It is represented by a peripheral section formed by taste buds located primarily in the mucous membrane of the tongue in mushroom-shaped, foliate and trough-shaped papillae; specific nerve fibers that reach the medulla oblongata, then the ventral and medial nuclei of the thalamus; subcortical and cortical structures located in the opercular region of the cerebral hemispheres and in the hippocampus. The sensitivity of different parts of the tongue to taste stimuli is not the same (the most sensitive: to sweet - the tip of the tongue, to sour - edges, to bitter - root, to salty - tip and edges). With prolonged action of taste stimuli, adaptation occurs, which occurs faster to sweet and salty substances, more slowly to sour and bitter ones.

The ability to distinguish odors provides an olfactory analyzer. It belongs to remote action devices and consists of a perceiving (receptor) apparatus, pathways and a part of the brain, where the highest analysis and synthesis of information about smells is carried out.

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sensory systems- these are specialized parts of the nervous system, including peripheral receptors (sensory organs, or sense organs), nerve fibers extending from them (pathways) and cells of the central nervous system grouped together (sensory centers). Each area of the brain that contains touch center (kernel) and switching nerve fibers, forms level sensory system. In the sensory organs, the energy of an external stimulus is converted into a nerve signal - reception. nerve signal (receptor potential) transforms into impulse activity or action potentials neurons (coding). Action potentials reach the sensory nuclei along the conduction pathways, on the cells of which the switching of nerve fibers and the transformation of the nerve signal take place. (transcoding). At all levels of the sensory system, simultaneously with the coding and analysis of stimuli, decoding signals, i.e. reading the touch code. Decoding is based on the connections of sensory nuclei with the motor and associative parts of the brain. Nerve impulses of axons of sensory neurons in the cells of motor systems cause excitation (or inhibition). The result of these processes is traffic- act or stop movement - inaction. The final manifestation of the activation of associative functions is also movement.

The main functions of sensory systems are:

signal reception;
conversion of the receptor potential into impulse activity of the nerve pathways;
transmission of nervous activity to sensory nuclei;
transformation of nervous activity in sensory nuclei at each level;
signal properties analysis;
identification of signal properties;
signal classification and identification (decision making).

12. Definition, properties and types of receptors.

Receptors are special cells or special nerve endings designed to transform energy (transformation) various kinds stimuli into specific activity of the nervous system (into a nerve impulse).

Signals entering the CNS from receptors cause either new reactions or change the course of what is happening in this moment activities.

Most receptors are represented by a cell equipped with hairs or cilia, which are such formations that act like amplifiers in relation to stimuli.

There is either a mechanical or biochemical interaction of the stimulus with the receptors. Thresholds for stimulus perception are very low.

According to the action of stimuli, receptors are divided into:

1. Interoreceptors

2. Exteroreceptors

3. Proprioreceptors: muscle spindles and Golgi tendon organs (discovered by I.M. Sechenov the new kind sensitivity - joint-muscular feeling).

There are 3 types of receptors:

1. Phase - these are receptors that are excited in the initial and final period of the stimulus.

2. Tonic - act during the entire period of the stimulus.

3. Phasno-tonic - in which impulses occur all the time, but more at the beginning and at the end.

The quality of perceived energy is called modality.

Receptors can be:

1. Monomodal (perceive 1 type of stimulus).

2. Polymodal (can perceive several stimuli).

The transfer of information from the peripheral organs occurs along sensory pathways, which can be specific and nonspecific.

Specific are monomodal.

Nonspecific are polymodal

Properties

Selectivity - sensitivity to adequate stimuli

Excitability - the minimum amount of energy of an adequate stimulus, which is necessary for the onset of excitation, i.e. arousal threshold.

Low threshold value for adequate stimuli

Adaptation (may be accompanied by both a decrease and an increase in the excitability of receptors. So, when moving from a bright room to a dark one, a gradual increase in the excitability of the photoreceptors of the eye occurs, and a person begins to distinguish dimly lit objects - this is the so-called dark adaptation.)

13. Mechanisms of excitation of primary-sensing and secondary-sensing receptors.

Primary sensory receptors: the stimulus acts on the dendrite of the sensory neuron, the permeability of the cell membrane to ions (mainly to Na +) changes, a local electrical potential (receptor potential) is formed, which electrotonically propagates along the membrane to the axon. An action potential is formed on the axon membrane, which is transmitted further to the CNS.

A sensory neuron with a primary sensory receptor is a bipolar neuron, on one pole of which there is a dendrite with a ciliary, and on the other - an axon that transmits excitation to the CNS. Examples: proprioceptors, thermoreceptors, olfactory cells.

Secondary sensory receptors: in them, the stimulus acts on the receptor cell, excitation occurs in it (receptor potential). On the axon membrane, the receptor potential activates the release of the neurotransmitter into the synapse, as a result of which a generator potential is formed on the postsynaptic membrane of the second neuron (most often bipolar), which leads to the formation of an action potential on neighboring sections of the postsynaptic membrane. This action potential is then transmitted to the CNS. Examples: hair cells in the ear, taste buds, photoreceptors in the eye.

!fourteen. Organs of smell and taste (localization of receptors, first switching, repeated switching, projection zone).

The organs of smell and taste are excited by chemical stimuli. Receptors of the olfactory analyzer are excited by gaseous, and taste - by dissolved chemicals. The development of the olfactory organs also depends on the way of life of animals. The olfactory epithelium is located away from the main respiratory tract and the inhaled air enters there by vortex movements or diffusion. Such vortex motions occur during “sniffing”, i.e. with short breaths through the nose and expansion of the nostrils, which facilitates the penetration of the analyzed air into these areas.

Taste Analyzer serves to determine the nature, palatability of the feed, its suitability for eating. Taste and olfactory analyzers help animals living in water to navigate in the environment, determine the presence of food, females. With the transition to life in the air, the value of the taste analyzer decreases. In herbivorous animals, the taste analyzer is well developed, which can be seen in the pasture and in the feeder, when the animals do not eat grass and hay all in a row.

The peripheral part of the taste analyzer is represented by taste buds located on the tongue, soft palate, posterior pharyngeal wall, tonsils and epiglottis. Taste buds are located on the surface of fungiform, foliate and trough papillae.

15. Skin analyzer (localization of receptors, first switching, repeated switching, projection zone).

Various receptor formations are located in the skin. The simplest type of sensory receptor is free nerve endings. Morphologically differentiated formations have a more complex organization, such as tactile discs (Merkel discs), tactile bodies (Meissner bodies), lamellar bodies (Pacini bodies) - pressure and vibration receptors, Krause flasks, Ruffini bodies, etc.

Most specialized end structures have a preferential sensitivity to certain types stimulation and only free nerve endings are polymodal receptors.

16. Visual analyzer (localization of receptors, first switching, repeated switching, projection zone).

The greatest amount of information (up to 90%) about outside world a person receives with the help of the organ of vision. The organ of vision - the eye - consists of the eyeball and an auxiliary apparatus. To auxiliary apparatus include eyelids, eyelashes, lacrimal glands and muscles of the eyeball. The eyelids are formed by folds of skin lined from the inside with a mucous membrane - the conjunctiva. The lacrimal glands are located in the outer upper corner of the eye. Tears wash over anterior section eyeball and through the nasolacrimal canal enter the nasal cavity. The muscles of the eyeball set it in motion and direct it towards the object in question
17. Visual analyzer. The structure of the retina. Formation of color perception. Conductor department. Information processing .

The retina has a very complex structure. It contains light-receiving cells - rods and cones. Rods (130 million) are more sensitive to light. They are called the apparatus of twilight vision. Cones (7 million) - this is a daytime and color vision. When these cells are stimulated by light rays, excitation occurs, which is carried through the optic nerve to the visual centers located in the occipital zone of the cerebral cortex. The area of the retina from which the optic nerve exits is devoid of rods and cones and therefore is not capable of perceiving light. It's called the blind spot. Almost next to it is a yellow spot formed by a cluster of cones - the place of the best vision.

The structure of the optical, or refractive, system of the eye includes: the cornea, aqueous humor, lens and vitreous body. In people with normal vision, the rays of light passing through each of these media are refracted and then enter the retina, where they form a reduced and inverted image of objects visible to the eye. Of these transparent media, only the lens is able to actively change its curvature, increasing it when looking at close objects and decreasing it when looking at distant objects. This ability of the eye to clearly see objects at different distances is called accommodation. If the rays are refracted too much when passing through transparent media, they are focused in front of the retina, resulting in myopia. In such people, the eyeball is either elongated or the curvature of the lens is increased. The weak refraction of these media leads to focusing of the rays behind the retina, which causes farsightedness. It occurs due to the shortening of the eyeball or flattening of the lens. Properly selected glasses can correct these Conducting paths of the visual analyzer. First, the second and third neurons of the visual analyzer pathway are located in the retina. The fibers of the third (ganglion) neurons in the optic nerve partially cross to form the optic chiasm (chiasm). After the decussation, the right and left visual tracts are formed. The fibers of the optic tract end in the diencephalon (the nucleus of the lateral geniculate body and the thalamus cushion), where the fourth neurons are located. visual pathway. A small number of fibers reach the midbrain in the region of the superior colliculi of the quadrigemina. The axons of the fourth neurons pass through the posterior leg of the internal capsule and are projected onto the cortex of the occipital lobe of the cerebral hemispheres, where cortical center visual analyzer. shortcomings of vision.

18. auditory analyzer(localization of receptors, first switching, repeated switching, projection zone). Conductor department. Information processing. auditory adaptation.

Auditory and vestibular analyzers. The organ of hearing and balance includes three sections: the outer, middle and inner ear. The outer ear consists of the auricle and the external auditory meatus. The auricle is represented by elastic cartilage, covered with skin, and serves to capture sound. The external auditory meatus is a canal 3.5 cm long, which begins with the external auditory opening and ends blindly with the tympanic membrane. It is lined with skin and has glands that secrete earwax.

Behind the tympanic membrane is the middle ear cavity, which consists of the tympanic cavity filled with air, the auditory ossicles and the auditory (Eustachian) tube. The auditory tube connects the tympanic cavity with the nasopharyngeal cavity, which helps to equalize pressure on both sides of the tympanic membrane. The auditory ossicles - the hammer, anvil and stirrup are movably connected to each other. The malleus is fused with the tympanic membrane with a handle, the head of the malleus is adjacent to the anvil, which is connected to the stirrup at the other end. The stirrup with a wide base connects to the membrane oval window leading to the inner ear. inner ear located in the thickness of the pyramid of the temporal bone; consists of a bony labyrinth and a membranous labyrinth located in it. The space between them is filled with fluid - perilymph, the cavity of the membranous labyrinth - endolymph. The bony labyrinth contains three sections: the vestibule, the cochlea, and the semicircular canals. The cochlea belongs to the organ of hearing, the rest of its parts - to the organ of balance.

The cochlea is a bony canal, twisted in the form of a spiral. Its cavity is divided by a thin membranous septum - the main membrane. It consists of numerous (about 24 thousand) connective tissue fibers different lengths. The receptor hair cells of the organ of Corti, the peripheral part of the auditory analyzer, are placed on the main membrane.

Sound waves through the external auditory meatus reach the tympanic membrane and cause its vibrations, which are amplified (almost 50 times) by the auditory ossicles and transmitted to the perilymph and endolymph, then perceived by the fibers of the main membrane. High sounds cause oscillations of short fibers, low sounds - longer, located at the top of the cochlea. These vibrations excite the receptor hair cells of the organ of Corti. Next, the excitation is transmitted through auditory nerve into the temporal lobe of the cerebral cortex, where the final analysis and synthesis of sound signals take place. The human ear perceives sounds with a frequency of 16 to 20 thousand Hz.

Conducting paths of the auditory analyzer. First neuron of the auditory analyzer pathways - the bipolar cells mentioned above. Their axons form cochlear nerve, the fibers of which enter the medulla oblongata and terminate in the nuclei, where the cells of the second neuron of the pathways are located. The axons of the cells of the second neuron reach the internal geniculate body, mainly on the opposite side. Here begins the third neuron, through which impulses reach the auditory region of the cerebral cortex.

In addition to the main pathway connecting the peripheral part of the auditory analyzer with its central, cortical part, there are other ways through which reflex reactions to irritation of the hearing organ in the animal can occur even after removal of the cerebral hemispheres. Of particular importance are orienting reactions to sound. They are carried out with the participation of the quadrigemina, to the posterior and partly anterior tubercles of which there are collaterals of fibers heading to the internal geniculate body.

19. Vestibular analyzer (localization of receptors, first switching, repeated switching, projection zone). Conductor department. Information processing .

vestibular apparatus. It is represented by the vestibule and semicircular canals and is an organ of balance. In the vestibule there are two sacs filled with endolymph. At the bottom and in the inner wall of the sacs are receptor hair cells, which are adjacent to the otolith membrane with special crystals - otoliths containing calcium ions. The three semicircular canals are located in three mutually perpendicular planes. The bases of the channels at the points of their connection with the vestibule form extensions - ampoules in which hair cells are located.

Receptors of the otolithic apparatus are excited by accelerating or decelerating rectilinear movements. The receptors of the semicircular canals are irritated by accelerated or slow rotational movements due to the movement of the endolymph. Excitation of the receptors of the vestibular apparatus is accompanied by a number of reflex reactions: a change in muscle tone, contributing to the straightening of the body and maintaining the posture. Impulses from the receptors of the vestibular apparatus through the vestibular nerve enter the central nervous system. The vestibular analyzer is connected to the cerebellum, which regulates its activity.

Conductive pathways of the vestibular apparatus. the path of the statokinetic apparatus carries out the transmission of impulses when the position of the head and body changes, participating together with other analyzers in the orientation reactions of the body relative to the surrounding space. The first neuron of the statokinetic apparatus is located in the vestibular ganglion, which lies at the bottom of the internal auditory canal. The dendrites of the bipolar cells of the vestibular ganglion form the vestibular nerve, formed by 6 branches: superior, inferior, lateral, and posterior ampullar, utricular, and saccular. They contact the sensitive cells of the auditory spots and scallops located in the ampullae of the semicircular canals, in the sac and uterine vestibule of the membranous labyrinth.

20. Vestibular analyzer. Building a sense of balance. Automatic and conscious control of body balance. Participation of the vestibular apparatus in the regulation of reflexes .

The vestibular apparatus performs the functions of perceiving the position of the body in space, maintaining balance. With any change in the position of the head, the receptors of the vestibular apparatus are irritated. The impulses are transmitted to the brain, from which nerve impulses are sent to the skeletal muscles in order to correct body position and movements. The vestibular apparatus consists of two parts: vestibule and semicircular canals, in which the receptors of the statokinetic analyzer are located.