Olfactory nerve. The centers of the sympathetic nervous system are

The olfactory organ in its peripheral section is represented by a limited area of the mucous membrane of the nasal cavity - the olfactory region covering the upper and partly the middle turbinates and the upper part of the nasal septum. The olfactory lining consists of olfactory neurosensory, supporting and basal cells. A person has about 6 million receptor cells (30,000 per 1 mm 2).

The central processes of the olfactory cells (I neuron) form olfactory nerves numbering 15-20 (nerviolfactorii), which pass through the perforated plate of the ethmoid bone into the cranial cavity and contact with the processes of the mitral nerve cells of the olfactory bulb (II neuron). The axons of the mitral cells pass along the olfactory tract and olfactory streaks to the primary cortical and subcortical olfactory centers (III neuron), and also as part of the medial bundles of the olfactory tracts reach the mitral cells of the opposite side.

The primary cortical centers of smell are the olfactory triangle, the anterior perforated substance, the transparent septum, and the cortex of the subcallosal gyrus. The subcortical olfactory centers are represented by the nuclei of the mastoid bodies, the nuclei of the leashes and the amygdala.

An intermediate bundle approaches the neurons of the olfactory triangle, the anterior perforated substance and the nuclei of the transparent septum of its and the opposite side olfactory tract. The largest, lateral bundle of the olfactory tract goes directly to the neurons of the old cortex big brain in the hook and parahippocampal gyrus (secondary cortical olfactory centers), as well as to the olfactory part amygdala(where does Broca's diagonal stripe originate, connecting the hook to the precommissural septum). In addition, the axons of the third neurons located in the olfactory triangle, the anterior perforated substance and in the cortex of the subcallosal region also reach the cortex of the uncus and the parahippocampal gyrus as part of the medial and lateral longitudinal strips above the corpus callosum, which then unite as part of the gyrus fasciolaris and pass into the dentate gyrus and the hippocampus (archeocortex). From here, the transmission of nerve impulses along the fimbria of the hippocampus and the fornix to the nuclei of the mastoid bodies (IV neuron), which give rise to the mastoid-thalamic and mastoid-opercular pathways (tractus mamillothalamicus et tractus mamillotegmentalis). In addition, impulses are transmitted from the fornix along the fibers that go as part of the medullary strip of the thalamus to the nuclei of the leashes, from which then along the leash-interpeduncular path to the interpeduncular nucleus of the midbrain. As part of the brain strip, fibers from the precommissural septum and the terminal strip of the thalamus also pass to the nuclei of the leashes.

The mastoid-thalamic pathway ends in the anterior nuclei of the thalamus (V neuron). From these nuclei, olfactory impulses can be transmitted along the thalamo-cortical pathway (anterior thalamic radiation) to the neocortex of the frontal lobe, primarily to the cingulate gyrus (field 24) and to the superior frontal gyrus (field 32). Through the pathways described, olfactory stimuli are included in the limbic system.

The mastoid-tubular path goes in a downward direction to the upper hillocks of the roof of the midbrain, from where the tegmental-spinal and tegmental-nuclear paths to motor nuclei cranial nerves. These pathways carry out unconditioned reflex reactions of the muscles of the head, trunk and limbs to olfactory stimuli (sniffing, licking). In addition, the connection of the olfactory brain with the hypothalamus is carried out by the fibers of the terminal strip, starting from the amygdala and going to the preoptic and dorsomedial nuclei of the hypothalamus. The individual nuclei of the hypothalamus are interconnected by the medial bundle forebrain, continuing then to the rear longitudinal beam Schutz. This ensures a vegetative reaction to olfactory stimuli (salivation, palpitations, vasospasm, increased intestinal motility, etc.).

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A person can navigate in the world around him with the help of different kind analyzers. We have the ability to feel various phenomena of the external environment with the help of smell, hearing, sight and other senses. Each of us has different analyzers developed to varying degrees. In this article, we will try to understand how the olfactory analyzer works, and also analyze what functions it performs and what effect it has on health.

Definition of the olfactory organ

It is believed that a person can receive most of the information coming from the outside through vision, but in the absence of smell, the picture of the world would not be so exciting and bright for us. In general, smell, touch, sight, hearing - this is what helps a person to perceive the world correct and complete.

The olfactory system allows you to recognize those substances that have the ability to dissolve and volatility. It helps to perceive images of the world subjectively, through smells. The main purpose of the olfactory organ is to provide an opportunity to objectively assess the quality of air and food. Why the sense of smell disappears is of interest to many. More on this later.

The main functions of the olfactory system

Among all the features this body feelings can be identified as the most significant for human life:

Evaluation of food consumed for its edibility and quality. It is the sense of smell that allows us to determine how a particular product is suitable for consumption.
The formation of such a type of behavior as food.
It is the organ of smell that plays important role in preliminary adjustment of such an important system as the digestive system.
Allows you to identify substances that may be dangerous to humans. But this is not all the functions of the olfactory analyzer.
The sense of smell allows you to perceive pheromones, under the influence of which such a type of behavior as sexual can be formed and changed.
With the help of the olfactory organ, a person can navigate in his environment.

It is worth noting that in people who have lost their sight for one reason or another, the sensitivity of the olfactory analyzer often increases by an order of magnitude. This feature allows them to better navigate the outside world.

The structure of the organs of smell

This sensory system includes several departments. So, we can distinguish:

Peripheral department. Includes cells of the receptor type, which are located in the nose, in its mucous membrane. These cells have cilia wrapped in mucus. It is in it that the dissolution of substances that have a smell occurs. As a result, a chemical reaction occurs, which then transforms into nerve impulse. What else does the structure of the olfactory analyzer include?
Conductor department. This part of the olfactory system is represented by the olfactory nerve. It is along it that impulses from the olfactory receptors propagate, which then enter the anterior part of the brain, in which there is a so-called olfactory bulb. Primary Analysis data occurs in it, and after that there is a transmission of nerve impulses to the next section of the olfactory system.
Central department. This department is located immediately in two areas of the cerebral cortex - in the frontal and temporal. It is in this section of the brain that the final analysis of the information received takes place, and it is in this section that the brain forms the reaction of our body to the effects of smell. Here are the divisions of the olfactory analyzer that exist.

Let's consider each of them in more detail.

Peripheral olfactory system

The process of studying the olfactory system should begin with the first, peripheral section of the odor analyzer. This section is located directly in the nasal cavity. The mucous membrane of the nose in these parts is somewhat thicker and richly covered with mucus, which is a protective barrier against drying out and serves as an intermediary in removing the remnants of irritants at the end of their exposure process.

The contact of the odorous substance with the receptor cells occurs here. The epithelium is represented by two types of cells:

Cells of the second type have a pair of processes. The first reaches for the olfactory bulbs, and the second looks like a stick with a bubble covered with cilia at the end.

conductor department

The second section conducts nerve impulses and is actually neural pathways that form the olfactory nerve. It is represented by several bundles, passing into the visual tubercle.

This department is interconnected with the limbic system of the body. This explains why we experience different emotions when perceiving smells.

Central section of the olfactory analyzer

Conventionally, this department can be divided into two parts - the olfactory bulb and departments in the temporal lobe of the brain.

This department is located in close proximity to the hippocampus, in the frontal part of the piriform lobe.

Mechanism for odor perception

In order for the smell to be perceived effectively, the molecules must first be dissolved in the mucus that surrounds the receptors. After that, specific proteins built into the membrane of receptor cells interact with the mucus.

This contact can occur if there is a correspondence between the shapes of the molecules of the substance and proteins. Mucus performs the function of controlling the availability of receptor cells for stimulus molecules.

After the interaction between the receptor and the substance begins, the protein structure changes and sodium ion channels open in cell membranes. After that, sodium ions enter the membranes and excite positive charges, leading to a change in the polarity of the membranes.

Then the mediator is released from the receptor, and this leads to the formation of an impulse in the nerve fibers. Through these impulses, irritation is transmitted to the following sections of the olfactory system. How to restore the sense of smell will be described below.

Adaptation of the olfactory system

Olfactory system A person has such a feature as the ability to adapt. This occurs if the stimulus affects the sense of smell for a long time.

The olfactory analyzer can adapt for a different period of time. It can take from a few seconds to several minutes. The length of the adaptation period depends on the following factors:

The period of exposure to the odorous substance on the analyzer.
The concentration level of an odorous substance.
The speed of movement of air masses.

They sometimes say that the sense of smell has become aggravated. What does it mean? The sense of smell adapts quite rapidly to some substances. The group of such substances is quite large, and adaptation to their smell occurs very quickly. An example is our addiction to smell. own body or clothes.

However, we adapt to another group of substances either slowly or partially at all.

What role does the olfactory nerve play in this?

Theory of odor perception

At the moment, scientists claim that there are more than ten thousand distinguishable odors. However, all of them can be divided into seven main categories, the so-called primary odors:

flower group.
Mint group.
Muscular group.
Ether group.
Rotten group.
camphor group.
Caustic group.

They are included in the set of odorous substances for the study of the olfactory analyzer.

In the event that we feel a mixture of several smells, then our olfactory system is able to perceive them as a single, new smell. Molecules of odors of different groups have different shapes, and also carry a different electrical charge.

Different scientists adhere to different theories explaining the mechanism by which the perception of smells occurs. But the most common is the one according to which it is believed that membranes have several types of receptors that have different structure. They have a susceptibility to molecules of different shapes. This theory is called stereochemical. Why does the sense of smell disappear?

Types of olfactory disorders

Besides the fact that we all have a sense of smell different levels development, some may show disturbances in the functioning of the olfactory system:

Anosmia is a disorder in which a person is unable to perceive odors.
Hyposmia is a disorder in which there is a decrease in the sense of smell.
Hyperosmia - characterizes increased sensitivity to odors.
Parosmia is a distorted perception of the smell of substances.
Impaired differentiation.
The presence of olfactory hallucinations.
Olfactory agnosia is a disorder in which a person can smell but is unable to identify it.

It should be noted that over the course of life, a person loses sensitivity to different smells, that is, sensitivity decreases. Scientists have found that by the age of 50, a person is able to perceive approximately twice less odors than in youth.

Olfactory system and age-related changes

During prenatal development The child's olfactory system is the first to form the peripheral part. This process begins around the second month of development. By the end of the eighth month, the entire olfactory system is already fully formed.

Immediately after birth, it is already possible to observe how the child perceives smells. The reaction is visible in the movements of the facial muscles, the heart rate or the position of the child's body.

It is with the help of the olfactory system that the child is able to recognize the smell of the mother. The olfactory organ also serves essential component during the formation of digestive reflexes. As the child grows, his ability to differentiate odors increases significantly.

If we compare the ability to perceive and differentiate odors in adults and children aged 5-6 years, then in adults this ability is much higher.

In what cases does loss or decrease in sensitivity to odors occur?

As soon as a person loses sensitivity to smells or its level decreases, we immediately begin to wonder why this happened and how to fix it. Among the reasons that affect the severity of the perception of odors, there are:

SARS.
Damage to the nasal mucosa by bacteria.
Inflammatory processes that occur in the sinuses and nasal passages due to the presence of infection.
Allergic reactions.

Loss of smell is always in some way dependent on disturbances in the functioning of the nose. It is he who is the main organ that provides us with the ability to smell. Therefore, the slightest swelling of the nasal mucosa can cause disturbances in the perception of odors. Often, olfactory disorders indicate that rhinitis symptoms may soon appear, and in some cases, only upon recovery, it can be found that the sensitivity to odors has decreased.

How to restore the sense of smell?

In the event that after the transferred colds you have lost your sense of smell, how to return it, the attending physician will be able to tell. You will most likely be prescribed topical medications that are vasoconstrictors. For example, "Naftizin", "Farmazolin" and others. However, they should not be abused.

The use of these funds for a long time can provoke reverse effect- there will be swelling of the mucous membrane of the nasopharynx, and this can stop the process of restoring the sense of smell.

It should be noted that even before the start of recovery, you can begin to take measures in order to return the sense of smell to its previous level. It seems possible to do this even at home. For example, you can inhale with a nebulizer or do steam baths. Their purpose is to make the mucus in the nasal passages softer, and this can contribute to a faster recovery.

In this case, you can inhale ordinary steam or steam from the infusion of herbs with medicinal properties. You should do these procedures at least three times a day, for about 20 minutes. It is important that steam is inhaled through the nose and exhaled through the mouth. Such a procedure will be effective throughout the entire period of the disease.

You can also use methods traditional medicine. The main way to return the sense of smell as quickly as possible is inhalation. The most popular recipes include:

Inhalation of vapors of basil essential oil.
Steam inhalation with the addition of eucalyptus oil.
Steam inhalations with the addition lemon juice And essential oils lavender and mint.

In addition to inhalations, to restore the sense of smell, you can instill the nose with camphor and menthol oils.

They can also help restore the lost sense of smell:

The procedure for warming the sinuses using a blue lamp.
Cyclical tension and weakening of the muscles of the nose.
Washing with saline solutions.
Inhaling the aroma of medicinal herbs, such as chamomile, cumin or mint.
Usage medical tampons that are inserted into the nasal passages. They can be soaked mint oil mixed with propolis tincture in alcohol.
Reception of sage broth, which is very effective in the fight against ENT diseases.

If you regularly resort to at least a few of the above preventive measures, then the effect will not keep you waiting. Using such folk methods, the sense of smell can be returned even after a couple of years after you lost it, because the receptors of the olfactory analyzer will be restored.

Olfactory analyzer, its structure and functions. Modern theories odor perception. Adaptation and sensitivity of the olfactory sensory system.

With the participation of the olfactory analyzer, orientation in the surrounding space is carried out and the process of cognition of the external world takes place. It influences eating behavior, takes part in testing food for edibility, in setting up the digestive apparatus for food processing (according to the conditioned reflex mechanism), and also in defensive behavior, helping to avoid danger due to the ability to distinguish substances harmful to the body.

Structural and functional characteristics of the olfactory analyzer.

The peripheral section is formed by receptors of the upper nasal passage of the mucous membrane of the nasal cavity. Olfactory receptors in the nasal mucosa terminate in olfactory cilia. Gaseous substances dissolve in the mucus surrounding the cilia, then a nerve impulse occurs as a result of a chemical reaction.

The conduction department is the olfactory nerve. Through the fibers of the olfactory nerve, impulses arrive at the olfactory bulb (the structure of the forebrain in which information is processed) and then follow to the cortical olfactory center.

The central section is a cortical olfactory center located on the lower surface of the temporal and frontal lobes of the cerebral cortex. In the cortex, the smell is determined and an adequate reaction of the body to it is formed.

The olfactory analyzer includes:

Peripheral department The analyzer is located in the thickness of the mucous membrane of the upper nasal passage and is represented by spindle-shaped cells with two processes each. One process reaches the surface of the mucosa, ending here with a thickening, the other (together with other process filaments) constitutes the conductive section. The peripheral part of the olfactory analyzer is the primary sensory receptors, which are the endings of the neurosecretory cell. The upper part of each cell carries 12 cilia, and an axon departs from the base of the cell. Cilia are immersed in a liquid medium - a layer of mucus produced by Bowman's glands. The presence of olfactory hairs significantly increases the contact area of the receptor with molecules of odorous substances. The movement of the hairs provides an active process of capturing the molecules of the odorous substance and contact with it, which underlies the targeted perception of odors. The receptor cells of the olfactory analyzer are immersed in the olfactory epithelium lining the nasal cavity, in which, in addition to them, there are supporting cells that perform a mechanical function and are actively involved in the metabolism of the olfactory epithelium.

The peripheral part of the olfactory analyzer is located in the mucous membrane of the upper nasal passage and the opposite part of the nasal septum. It is represented olfactory And supporting cells. Around each supporting cell there are 9-10 olfactory . Olfactory cells are covered with hairs, which are threads 20-30 microns long. They bend and unbend at a speed of 20-50 times per minute. Inside the hairs are fibrils, which usually go into a thickening - a button at the end of the hair. In the body of the olfactory cell and in its peripheral process is located a large number of microtubules with a diameter of 0.002 μm, suggest that they communicate between various cell organelles. The body of the olfactory cell is rich in RNA, which forms dense clusters near the nucleus. After exposure to odorous vapors

Rice. 70. Peripheral olfactory analyzer:

d- diagram of the structure of the nasal cavity: 1 - lower nasal passage; 2 - bottom, 3 - average and 4 - superior turbinates; 5 - upper nasal passage; B- diagram of the structure of the olfactory epithelium: 1 - the body of the olfactory cell, 2 - supporting cell; 3 - mace; 4 - microvilli; 5 - olfactory threads.

substances, their loosening and partial disappearance occur, which indicates that the function of olfactory cells is accompanied by changes in the distribution of RNA and in its quantity.

The olfactory cell has two processes. One of them, through the holes of the perforated plate of the ethmoid bone, goes into the cranial cavity to the olfactory bulbs, in which excitation is transmitted to the neurons located there. Their fibers form olfactory pathways that reach different parts of the brain stem. The cortical region of the olfactory analyzer is located in the hippocampal gyrus and in the ammon horn.

The second process of the olfactory cell has the shape of a stick 1 µm wide, 20-30 µm long and ends with an olfactory vesicle - a club with a diameter of 2 µm. There are 9-16 cilia on the olfactory vesicle.

conductor department represented by conducting nerve pathways in the form of an olfactory nerve leading to the olfactory bulb (oval-shaped formation). Conductor department. The first neuron of the olfactory analyzer should be considered a neurosensory or neuroreceptor cell. The axon of this cell forms synapses, called glomeruli, with the main dendrite of the mitral olfactory bulb cells, which represent the second neuron. The axons of the mitral cells of the olfactory bulbs form the olfactory tract, which has a triangular extension (olfactory triangle) and consists of several bundles. The fibers of the olfactory tract go in separate bundles to the anterior nuclei of the optic tubercle.

Central department consists of the olfactory bulb connected by branches of the olfactory tract with centers located in the paleocortex (the ancient cortex of the cerebral hemispheres) and in subcortical nuclei, as well as the cortical department, which is localized in temporal lobes brain, gyrus of a sea horse.

The central, or cortical, section of the olfactory analyzer is localized in the anterior part of the pear-shaped lobe of the cortex in the region of the seahorse gyrus.

Perception of smells. Molecules of an odorous substance interact with specialized proteins built into the membrane of olfactory hair neurosensory receptor cells. In this case, the adsorption of stimuli on the chemoreceptor membrane occurs. According to stereochemical theory this contact is possible if the shape of the odorant molecule corresponds to the shape of the receptor protein in the membrane (like a key and a lock). The mucus covering the surface of the chemoreceptor is a structured matrix. It controls the availability of the receptor surface for stimulus molecules and is able to change the conditions of reception. Modern theory olfactory reception suggests that initial link In this process, there can be two types of interaction: the first is contact charge transfer during the collision of odorous substance molecules with the receptive site, and the second is the formation of molecular complexes and complexes with charge transfer. These complexes are necessarily formed with protein molecules of the receptor membrane, the active sites of which act as donors and acceptors of electrons. An essential point of this theory is the position on multipoint interactions of molecules of odorous substances and receptive sites.

Features of adaptation of the olfactory analyzer. Adaptation to the action of an odorous substance in the olfactory analyzer depends on the air flow velocity over the olfactory epithelium and the concentration of the odorous substance. Usually, adaptation is shown in relation to one smell and may not affect other smells.

Perception of olfactory stimuli. Olfactory receptors are very sensitive. To excite one human olfactory cell, from 1 to 8 molecules of an odorous substance (butyl mercaptan) is sufficient. The mechanism of odor perception has not yet been established. It is assumed that the olfactory hairs are, as it were, specialized antennas that are actively involved in the search for and perception of odorous substances. Regarding the mechanism of perception, there are different points vision. Thus, Eimur (1962) believes that on the surface of the hairs of olfactory cells there are special receptive areas in the form of pits, slits of a certain size and charged in a certain way. Molecules of various odorous substances have a shape, size and charge that are complementary to different parts of the olfactory cell, and this determines the difference between odors.

Some researchers believe that the olfactory pigment present in the olfactory receptive zone is also involved in the perception of olfactory stimuli, as is the retinal pigment in the perception of visual stimuli. According to these ideas, the colored forms of the pigment contain excited electrons. Odorous substances, acting on the olfactory pigment, cause the transition of electrons to a lower energy level, which is accompanied by discoloration of the pigment and the release of energy that is spent on the occurrence of impulses.

Biopotentials arise in the mace and spread further along the olfactory pathways to the cerebral cortex.

Molecules of an odorous substance bind to receptors. Signals from receptor cells enter the glomeruli (glomeruli) of the olfactory bulbs - small organs located in the lower part of the brain just above the nasal cavity. Each of the two bulbs contains approximately 2000 glomeruli - twice as many as there are types of receptors. Cells that have receptors of the same type send a signal to the same balls of bulbs. From glomeruli, signals are transmitted to mitral cells - large neurons, and then to special areas of the brain, where information from different receptors is combined to form an overall picture.

According to the theory of J. Aymour and R. Moncrieff (stereochemical theory), the smell of a substance is determined by the shape and size of the odorous molecule, which, according to its configuration, approaches the receptor site of the membrane “like a key to a lock”. The concept of receptor sites different type that interact with specific odorant molecules suggests the presence of seven types of receptor sites (according to the types of odors: camphor, ethereal, floral, musky, pungent, minty, putrid). Receptive sites are in close contact with odorant molecules, while the charge of the membrane site changes and a potential arises in the cell.

According to Eimur, the whole bouquet of smells is created by a combination of these seven components. In April 1991, the staff of the Institute. Howard Hughes (Columbia University) Richard Axel and Linda Buck found that the structure of the receptor sites in the membrane of olfactory cells is genetically programmed, and there are more than 10 thousand species of such specific sites. Thus, a person is able to perceive more than 10 thousand smells.

Adaptation of the olfactory analyzer can be observed at long acting odor stimulus. Adaptation to the action of an odorous substance occurs rather slowly within 10 seconds or minutes and depends on the duration of the action of the substance, its concentration and the speed of air flow (sniffing).

In relation to many odorous substances, complete adaptation occurs rather quickly, i.e., their smell ceases to be felt. A person ceases to notice such continuously acting stimuli as the smell of his body, clothes, room, etc. In relation to a number of substances, adaptation occurs slowly and only partially. With a short-term action of a weak taste or olfactory stimulus: adaptation may manifest itself in an increase in the sensitivity of the corresponding analyzer. It has been established that changes in sensitivity and adaptation phenomena mainly occur not in the peripheral, but in the cortical section of the gustatory and olfactory analyzers. Sometimes, especially with the frequent action of the same taste or olfactory stimulus, a persistent focus of increased excitability appears in the cerebral cortex. In such cases, the sensation of taste or smell, to which increased excitability has arisen, may also appear under the action of various other substances. Moreover, the sensation of the corresponding smell or taste can become intrusive, appearing even in the absence of any taste or smell stimuli, in other words, illusions and hallucinations arise. If during lunch you say that the dish is rotten or sour, then some people have the corresponding olfactory and gustatory sensations, as a result of which they refuse to eat.

Adaptation to one odor does not reduce sensitivity to odorants of another type, because various odorous substances act on different receptors.

the third is blue. Depending on the degree of excitation of the cones and the combination of stimuli, various other colors and their shades are perceived.

The eye must be protected from mechanical influences, read in a well-lit room, holding the book at a certain distance (up to 33-35 cm from the eye). The light should fall on the left. You can not lean close to the book, since the lens in this position is in a convex state for a long time, which can lead to the development of myopia. Too bright lighting harms vision, destroys light-perceiving cells. Therefore, steelworkers, welders and other similar professions are advised to wear dark safety goggles while working. You can not read in a moving vehicle. Due to the instability of the position of the book, the focal length changes all the time. This leads to a change in the curvature of the lens, a decrease in its elasticity, as a result of which the ciliary muscle weakens. Visual impairment can also occur due to a lack of vitamin A.

Olfactory analyzer(Fig. 408). Sense of smell is the ability to perceive smells. The receptors are located in the mucous membrane of the upper and middle nasal passages.

Figure 408. Olfactory analyzer. The olfactory bulb is a membrane that collects impulses from olfactory cells. Nerve branches - nerves that transmit impulses from olfactory cells to the olfactory bulb. The red mucous membrane is the mucous membrane that lines the outer part of the nasal cavity and warms the inhaled air. The olfactory nerve is the nerve that transmits olfactory impulses to the cerebral cortex. Yellow mucosa is the mucous membrane that lines the upper part of the nasal cavity and contains olfactory cells.

A person has a different degree of smell for various odorous substances. Pleasant smells improve a person’s well-being, while unpleasant ones act depressingly, cause negative reactions up to nausea, vomiting, fainting (hydrogen sulfide, gasoline), can change skin temperature, cause disgust for food, lead to depression and irritability. The smell can serve as a warning signal of danger. Everyone knows how dangerous gases are. To recognize dangerous, odorless gases, special strongly smelling substances, odorants, are added to them. There are no widely used devices for measuring the strength of smell yet. However, our nose instantly feels even the smallest fractions of odorous substances.

Receptors of the olfactory sensory system are located in the region of the upper nasal passages. The olfactory epithelium contains receptor cells. Humans have about 60 million olfactory cells. They are located in the mucous membrane of the turbinates on an area of approximately 5 cm2. Cells covered huge amount hairs 30-40 angstroms (3-4 nanometers) long. The area of their contact with odorous substances is 5-7 m2. depart from the olfactory cells nerve fibers that send signals about smells to the brain.

If the analyzers are exposed to a substance hazardous to life or health threatening human (ether, ammonia, chloroform, etc.), reflexively slows down or breath is held for a short time.

Upon contact of the sensitive hairs of the receptors with molecules of odorous substances, a potential is generated in the receptor, which reaches the olfactory bulb (the primary nerve center of the olfactory analyzer) through the fibers of the olfactory nerve.

The progressive development of receptors in ontogeny ends already in embryonic period. After 30 years, there is a decrease in the number of olfactory cells. This process especially sharply increases in 50-60 years.

The sensitivity of the olfactory analyzer is determined by the mimic reaction of the child when bringing cotton wool moistened with an odorous solution to the nose. The data obtained as a result of the research testify to the low excitability of the olfactory analyzer of newborns. Excitability reaches the level of an adult by the age of 14 and worsens after 45 years.

The olfactory organ (organum olfactus) (Fig. 409) is a peripheral part of the olfactory analyzer and perceives chemical irritations when steam or gas enters the nasal cavity. The olfactory epithelium (epithelium olfacctorium) is located in the upper part of the nasal passage and the posterior superior part of the nasal septum, in the mucous membrane of the nasal cavity. This section is called the olfactory region of the nasal mucosa (regio olfactoria tunicae mucosae nasi). It contains the olfactory glands (glandulae olfactoriae).

The lower part of the shell is lined with a red mucous membrane rich in blood vessels that warm the inhaled air. In the yellow mucous membrane, or olfactory membrane, three layers of cells are distinguished: structural cells, olfactory cells and basal cells. Olfactory cells are nerve cells, which perceive chemical stimuli in the form

Figure 409. The organ of smell. vapors. The yellow mucosa also houses Bowman's mucous glands, which secrete a fluid that keeps the olfactory epithelium moist and clean.

In order to excite the olfactory cells, substances must be volatile, that is, they must give off vapors that could penetrate into nasal cavity, and be soluble in water enough to dissolve in mucus and reach the olfactory cells. The latter transmit a nerve impulse to the olfactory bulb, and from there to the olfactory centers of the cerebral cortex, where the sensation is evaluated and deciphered.

It is believed that there are about seven types of olfactory receptors, each of which is able to detect only one type of molecule.

Figure 410. These main olfactory odors are as follows: camphor (smell of camphor), olfactory pathways. musky (smell of musk), floral, minty, ethereal (smell of ether), acrid and putrid (smell of rot). Olfactory receptors get tired: after prolonged perception of the same substance, they cease to emit nerve impulses to this substance, but continue to remain sensitive to all other odors.

It is not known what needs to be done in terms of chemistry in order to excite the olfactory cells, but it is known physical characteristics substances that cause olfactory irritation: they must be volatile, slightly soluble in water, and also to some extent in lipids.

In addition, the olfactory cells are excited only when air penetrates upward into the back nasal cavity.

Chemoreceptors transmit the nerve impulse to the olfactory bulb, and it - to the olfactory centers of the cerebral cortex, where sensations are evaluated and deciphered.

The organ of taste (organum custus) is a peripheral part of the taste analyzer and is located in the oral cavity. Taste is a sensation that occurs when certain water-soluble chemicals are exposed to taste buds located on different parts of the tongue.

Taste is made up of four simple taste sensations: sour, salty, sweet, and bitter. All other flavors

These are combinations of basic sensations. Different parts of the tongue have different sensitivity to taste substances: the tip of the tongue is sensitive to sweet, the edges of the tongue to sour, the tip and edge of the tongue to salty, the root of the tongue to bitter. The mechanism of perception of taste sensations is associated with chemical reactions. It is assumed that each receptor contains highly sensitive protein substances that decompose when exposed to certain flavoring substances.

Taste, like smell, is based on chemoreception. Taste buds carry information about the nature and concentration of substances entering the oral cavity. Taste receptors - taste buds - are located on the tongue, back of the throat, soft palate. Most of them are on the tip of the tongue.

Figure 411. Scheme The taste bud does not reach the mucosal surface of the taste tract. tongue and is connected to the oral cavity through the taste pore. Taste cells, there are about 10,000 of them, on average after 250 hours they are replaced by a young cell, that is, taste buds have a short time life. They become excited during absorption.

on the walls of microvilli of various substances.

The morphogenesis of the receptor apparatus of the taste analyzer is completed in the prenatal period.

In a newborn, taste sensitivity has a larger surface of the mouth than in adults. This is due to the fact that in newborns, taste buds are found on the entire back of the tongue, on the hard palate, and even on the buccal mucosa. After birth, the number of taste buds decreases. One of the most early research taste sensitivity in newborns was based on the observation of facial reactions to the application of several drops of solutions of bitter, sour and sweet substances of different concentrations to the tongue. Based on these data, for example, the threshold concentration of the perception of sweets was determined in its concentration, which is only 1%. The study of taste sensitivity in more than wide range show that it is optimal at 20-30 years old, and then gradually decreases, especially actively after 70 years.

Thus, in the activity of the taste analyzer in early periods In the postnatal life of a person, there is a discrepancy between the reduced sensitivity of receptors compared to adults and a more extensive receptor zone.

In physiology and psychology, the four-component theory of taste is accepted, according to which taste has four main types: sweet, salty, sour and bitter. All other taste sensations are a combination of the main types.

Taste is perceived by special cell formations (similar to bulbs) located in the mucous membrane of the tongue.

The discriminating sensitivity of the taste analyzer is rather crude, however, taste sensations play a precautionary role in ensuring safety.

The taste analyzer is about 10 thousand times coarser than the sense of smell, individual perception of taste can vary up to 20%.

Taste receptors are composed of neuroepithelial cells, contain branches of the taste nerve and are called taste buds.

Language (Fig. 412) is muscular organ, which, being the organ of taste, is also involved in swallowing and articulating speech.

Its entire surface, with the exception of the base, is covered with a mucous membrane in which papillae are located - chemical receptors for taste excitations.

The papillae are divided according to their shape. Only groove-shaped papillae, surrounded by a shaft, forming the Latin letter V, and mushroom-shaped papillae located at the tip, edges and back side of the tongue, truly perform the function of taste analyzers, since they are the only ones that have taste buds. Foliate papillae perform a tactile function and are sensitive to temperature changes. Taste buds are ovoid and

Figure 412. Language. formed by 5-20 receptor cells, several supporting cells, several taste hairs and a small pore opening to the mucous membrane of the tongue. The papillae are sensitive to four main taste stimuli: sweet, salty, sour and bitter, the ratio and intensity of which enable the brain to recognize the product in which they are contained.

In order for a substance to excite the taste buds, it must be liquid or dissolved in saliva in order to enter the taste pore. When excited, various cell receptors produce a nerve impulse that enters the medulla, and from there to the taste zone of the mountains of the brain. Sensitive innervation is carried out by the vagus and glossopharyngeal nerves, and motor innervation is carried out by the facial nerve.

Taste buds are not evenly distributed over the entire surface of the tongue, but form zones of greater or lesser concentration. These separate sensitive areas are specialized for a certain taste: for example, the kidneys that are sensitive to sweets are located mainly on the surface of the front of the tongue; the kidneys that catch sour are on both sides of the tongue, the kidneys that perceive bitter are at the back of the tongue, and those sensitive to salt are scattered throughout the tongue.

Many foods are known to represent these four tastes: lemons (sour), salt (salty), coffee (bitter), cakes (sweet).

Figure 413. Substances that cause basic taste sensations can be the most taste bud. different, since they usually do not depend on only one single chemical agent. For example, many substances used in medicine, such as quinine, caffeine, strychnine, and nicotine, are bitter. One of the sweetest natural products is sucrose (sugar from sugar cane), but much sweeter is saccharin, a synthetic sweetener, as well as some other substances of organic origin.

Taste buds (gemma gustatoria) are oval in shape and are located mainly in leaf-shaped, mushroom-shaped and grooved papillae of the mucous membrane of the tongue (see section " Digestive system"). In small quantities, they are found in the mucous membrane of the anterior surface of the soft palate, epiglottis and rear wall throats.

Irritations perceived by the bulbs go to the nuclei of the brain stem, and then to the region of the cortical end of the taste analyzer.

Receptors are able to distinguish four basic tastes: sweet is perceived by receptors located at the tip of the tongue, bitter by receptors located at the root of the tongue, salty and sour by receptors at the edges of the tongue.

Skin Analyzer perceives external mechanical, temperature, chemical and other skin irritants. The skin (cutis) is the general covering of the body, the area

which reaches 1.5–2.0 m2. 1 cm2 of skin contains up to 300 sensitive nerve endings.

In addition to the tactile function, the skin performs a protective function, protecting the organs and parts of the body located under it from damage, prevents the penetration of harmful substances and microorganisms, and plays an important role in the process of respiration, water and heat exchange.

The receptor function of the skin is perception from the outside and transmission of signals to the central nervous system. Skin receptors perceive tactile, temperature and pain stimuli.

Touch is a complex sensation that occurs when the receptors of the skin, the outer parts of the mucous membranes and the muscular-articular apparatus are irritated. The tactile receptor is a touch receptor located in the papillary, outermost layer of the skin.

Part of these functions (primarily protective) is provided by epithelial tissue (textus epitheliales), which covers the outer surface of the body and promotes the metabolism between the body and external environment. The superficial layer of the skin is called the cuticle, or epidermis (epidermis), and is a multi-layered, constantly keratinizing epithelium. The thickness of the epidermis is from 0.07 to 0.4 mm.

The second layer of the skin - the actual skin, or dermis (dermis) - is a fibrous connective tissue.

In the dermis, a deeper reticular layer (stratum reticulare) and a superficial papillary layer (stratum papillae) are distinguished. On the surface of the papillary layer are papillae that grow into the epidermis. There are loops in the grooves between the papillae. blood vessels and nerve endings, which, together with nerve endings reticular layer are receptors that perceive tactile stimuli.

The skin serves as the first protective barrier at the moment the current-carrying conductor touches the body. Possessing a high electrical resistance, sometimes reaching tens of thousands of ohms, the skin, at the first moment, prevents the passage electric current through internal organs which allows you to turn on

other types of body defense.

Functional impairment 30-50% skin, in the absence of special medical care leads to the death of a person.

There are approximately 500 thousand points on the skin - tactile analyzers that perceive sensations that arise when various mechanical stimuli (touch, pressure) are exposed to the skin surface. In addition, on the skin

Figure 414. Skin incision and there are unevenly distributed analyzes tactile receptors. ry, perceiving pain, heat and cold.

Most high sensitivity on the distal parts of the body (the furthest from the axis of the body).

The tactile analyzer has high ability to spatial localization. Its characteristic feature is the rapid development of adaptation (addiction), i.e. loss of feeling of touch or pressure. The adaptation time depends on the strength of the stimulus, for different parts of the body it ranges from 2 to 20 seconds. Thanks to adaptation, we do not feel the touch of clothes on the body.

Temperature sensitivity is characteristic of organisms with constant temperature body achieved by thermoregulation. The skin temperature is lower than the internal body temperature (approximately 36.6 ° C) and is different for individual areas (on the forehead 34-35, on the face 20-25, on the stomach 34, on the soles of the feet 25-27 ° C).

There are two types of temperature analyzers in human skin: some react only to cold, others only to heat. In total, there are about 30 thousand heat points and approximately 250 thousand cold points on the skin.

Peripheral section of the olfactory analyzer: e - diagram of the structure of the nasal cavity: 1 - lower nasal passage; 2 - lower, 3 - middle and 4 - upper turbinates; 5 - upper nasal passage; B - diagram of the structure of the olfactory epithelium: 1 - body of the olfactory cell, 2 - supporting cell; 3 - mace; 4 - microvilli; 5 - olfactory threads

The olfactory cell has two processes. One of them, through the holes of the perforated plate of the ethmoid bone, goes into the cranial cavity to the olfactory bulbs, in which it is transmitted to those located there. Their fibers form olfactory pathways that are suitable for various departments. The cortical region of the olfactory analyzer is located in the hippocampal gyrus and in the ammon horn.

substances, their loosening and partial disappearance occur, which indicates that the function of olfactory cells is accompanied by changes in the distribution of RNA and in its quantity.

The olfactory cell has two processes. One of them, through the holes of the perforated plate of the ethmoid bone, goes into the cranial cavity to the olfactory bulbs, in which excitation is transmitted to the neurons located there. Their fibers form olfactory pathways that are suitable for various departments. The cortical region of the olfactory analyzer is located in the hippocampal gyrus and in the ammon horn.

Central department It consists of an olfactory bulb connected by branches of the olfactory tract with centers located in the paleocortex (the ancient cortex of the cerebral hemispheres) and in the subcortical nuclei, as well as a cortical section, which is localized in the temporal lobes of the brain, the gyrus of the sea horse.

The central, or cortical, section of the olfactory analyzer is localized in the anterior part of the pear-shaped lobe of the cortex in the region of the seahorse gyrus.

Perception of smells. Molecules of an odorous substance interact with specialized proteins built into the membrane of olfactory hair neurosensory receptor cells. In this case, the adsorption of stimuli on the chemoreceptor membrane occurs. According to stereochemical theory this contact is possible if the shape of the odorant molecule corresponds to the shape of the receptor protein in the membrane (like a key and a lock). The mucus covering the surface of the chemoreceptor is a structured matrix. It controls the availability of the receptor surface for stimulus molecules and is able to change the conditions of reception. Modern theory Olfactory reception suggests that the initial link in this process can be two types of interaction: the first is contact charge transfer during the collision of odorous substance molecules with the receptive site, and the second is the formation of molecular complexes and complexes with charge transfer. These complexes are necessarily formed with protein molecules of the receptor membrane, the active sites of which act as donors and acceptors of electrons. An essential point of this theory is the position on multipoint interactions of molecules of odorous substances and receptive sites.

Olfactory receptors are very sensitive. To excite one human olfactory cell, from 1 to 8 molecules of an odorous substance (butyl mercaptan) is sufficient. The mechanism of odor perception has not yet been established. It is assumed that the olfactory hairs are, as it were, specialized antennas that are actively involved in the search for and perception of odorous substances. Regarding the mechanism of perception, there are different points. Thus, Eimur (1962) believes that on the surface of the hairs of olfactory cells there are special receptive areas in the form of pits, slits of a certain size and charged in a certain way. Molecules of various odorous substances have a shape, size and charge that are complementary to different parts of the olfactory cell, and this determines the difference between odors.

Biopotentials arise in the mace and spread further along the olfactory pathways to the cerebral cortex.

Molecules of an odorous substance bind to receptors. Signals from receptor cells are sent to the glomeruli (glomeruli) of the olfactory bulbs, small organs located in the lower part of the brain just above the nasal cavity. Each of the two bulbs contains approximately 2000 glomeruli - twice as many as there are types of receptors. Cells that have receptors of the same type send a signal to the same balls of bulbs. From glomeruli, signals are transmitted to mitral cells - large neurons, and then to special areas of the brain, where information from different receptors is combined to form an overall picture.

According to the theory of J. Aymour and R. Moncrieff (stereochemical theory), the smell of a substance is determined by the shape and size of the odorous molecule, which, according to its configuration, approaches the receptor site of the membrane “like a key to a lock”. The concept of different types of receptor sites interacting with specific odorant molecules suggests the presence of seven types of receptor sites (according to the types of odors: camphor, ethereal, floral, musky, pungent, minty, putrid). Receptive sites are in close contact with odorant molecules, while the charge of the membrane site changes and a potential arises in the cell.

Adaptation of the olfactory analyzer can be observed with prolonged exposure to an odor stimulus. Adaptation to the action of an odorous substance occurs rather slowly within 10 seconds or minutes and depends on the duration of the action of the substance, its concentration and the speed of air flow (sniffing).

In relation to many odorous substances, complete adaptation occurs rather quickly, i.e., their smell ceases to be felt. A person ceases to notice such continuously acting stimuli as the smell of his body, clothes, room, etc. In relation to a number of substances, adaptation occurs slowly and only partially. With a short-term action of a weak taste or olfactory stimulus: adaptation may manifest itself in an increase in the sensitivity of the corresponding analyzer. It has been established that changes in sensitivity and adaptation phenomena mainly occur not in the peripheral, but in the cortical section of the gustatory and olfactory analyzers. Sometimes, especially with the frequent action of the same taste or olfactory stimulus, a persistent focus of increased excitability appears in the cerebral cortex. In such cases, the sensation or smell to which increased excitability has arisen may also appear under the action of various other substances. Moreover, the sensation of the corresponding smell or taste can become intrusive, appearing even in the absence of any taste or smell stimuli, in other words, illusions and hallucinations arise. If during lunch you say that the dish is rotten or sour, then some people have the corresponding olfactory and gustatory sensations, as a result of which they refuse to eat.

Adaptation to one odor does not reduce sensitivity to odorants of another type, because different odorants act on different receptors.