A form of sensitivity, one of the types of chemoreception.

Sensitivity of oral cavity receptors to chemical irritants. Subjectively manifested in the form of taste sensations (bitter, sour, sweet, salty and their complexes). When alternating a number of chemicals, a taste contrast may occur (after salty, fresh water seems sweet). A holistic taste image arises due to the interaction of taste, tactile, temperature, olfactory receptors.

To explain the mechanism of formation of taste sensations, two hypotheses have been put forward: analytical and enzymatic.

Psychological Dictionary. THEM. Kondakov. 2000 .

See what "taste sensitivity" is in other dictionaries:

Taste sensitivity- the ability to perceive and transmit information about chemical stimuli through taste buds or taste buds located on the surface of the tongue, throat and larynx (approximately 10,000 tubercles up to 2 mm in size with contained ... ... Encyclopedic Dictionary of Psychology and Pedagogy

Sensitivity- I Sensitivity (sensibilitas) - the ability of the body to perceive various stimuli emanating from the external and internal environment, and respond to them. Ch. is based on the processes of reception, the biological significance of which lies in ... ... Medical Encyclopedia

Sensitivity- (sensibilitas) - the ability of the body to perceive stimuli of the external and internal environments and, accordingly, to respond to them, is also inherent in individual cells: pain, vibration, visceral, taste, deep, differential, skin, ... ... Glossary of terms for the physiology of farm animals

taste sensitivity- (s. gustatoria) Ch. to chemical effects, realized by the appearance of a sensation of taste of the acting substance ... Big Medical Dictionary

Sensitivity Gustation- Taste or gustatory perception. Source: Medical Dictionary... medical terms

TASTE- a sensation that occurs when various food and non-food (for example, some chemical and medicinal) substances enter the oral cavity. Taste sensations can only be caused by substances that are in a dissolved state. ... ... The Concise Encyclopedia of the Household

TASTE- sensation arising from the action of chemical solutions. substances on taste receptors in animals. Main taste sensations sour, salty, sweet, bitter are defined as the configuration of the molecules of substances adsorbed on a specific. receptors... ... Biological encyclopedic dictionary

HUMAN NERVES- HUMAN NERVES. [Anatomy, physiology and pathology of the nerve, see Art. Nerves in Volume XX; ibid. (Art. 667 782) drawings of human nerves]. Below is a table of nerves, illuminating in a systematic manner the most important points in the anatomy and physiology of each ... ... Big Medical Encyclopedia

Perceptual abilities of babies (infant perceptual abilities)- General characteristics of the infant's perception In his Principles of psychology (“Principles of psychology”), W. James described the perceptual world of the infant as follows: “A baby attacked by stimuli that simultaneously come from the eyes, ears, nose, skin and ... ... Psychological Encyclopedia

Glossopharyngeal nerve- Scheme of the glossopharyngeal, vagus and accessory nerves ... Wikipedia

The taste buds on the tongue respond to stimuli located in the mouth. In other words, taste sensitivity in all vertebrates is involved in orientation at close range. At the same time, in fish, the sense of taste can also serve as orientation at a long distance. In water, flavoring substances move by diffusion and convection from very distant sources to taste buds, which can be dispersed over the entire surface of the fish's body.

In addition to its role in orientation at close range, the human sense of taste performs an important function by triggering a series of reflexes. For example, washing the tongue with a secret from the serous glands is controlled by a reflex that is under the influence of taste buds. The secretion of saliva is also triggered reflexively by appropriate stimulation of the taste buds. Even the composition of saliva varies depending on the nature of the stimuli acting on sensory cells, and gustatory stimuli also affect the secretion of gastric juice. Finally, it has been proven that vomiting is induced with the participation of taste sensitivity.

Literature

• 1. Batuev A.S., Kulikov G.L. Introduction to the physiology of sensory systems. - M.: Higher School, 1983. -263 p.
• 2. Lectures on the physiology of the central nervous system: Textbook. Faculty of Biology and Chemistry, UdSU, Pronichev I.V. -- Powered by swift.engine.edu, 2003. - 162 p.
• 3. Shulgovskiy VV Fundamentals of neurophysiology: Textbook for university students. -- M.: Aspect Press, 2000. p. 277.
• 4. Shulgovsky VV Physiology of higher nervous activity with the basics of neurobiology: Textbook for students of biol. specialties of universities. - M .: Publishing Center "Academy", 2003. - 464 p.

The ability to recognize the basic types of taste. The test of sensory sensitivity to recognize the main types of taste is carried out on model solutions of chemically pure substances:

To prepare solutions, distilled water treated with active carbon is used. The solutions are stored in flasks with a ground stopper at a temperature of 18-20°C. For testing, pour 35 ml of solution into tasting glasses. A total of nine samples are prepared: 2 glasses with any three solutions and 3 glasses with the fourth solution. The test subject does not need to know the order in which the samples are submitted. Between the samples make a 1-2-minute break, be sure to rinse your mouth with clean water. With seven or more correct answers, the candidate for tasters is recommended to complete the following test tasks.

Determination of an individual taste detection threshold.

In order to determine the threshold sensitivity to the main taste sensations, the expert is offered to try a series of solutions of increasing concentration (table). Each series consists of 12 solutions.

The concentration of model solutions (in g / dm 3) to determine individual taste thresholds

Solutions are prepared in distilled water treated with active carbon. The concentration is considered detected if the test solution is identified in three triangular comparisons. In each triple of solutions, two are the solvent, one is the test. They are served in ascending order, within one triplet, in a random sequence unknown to the subject. For instance:

The threshold sensitivity to the main types of taste in candidates for organoleptic analytics should be:

for sweet taste< 7,0 г/дм по сахарозе;

for salty taste< 1,5 г/дм по NaCl;

for sour taste< 0,5 г/дм по винной кислоте;

for bitter taste< 5,0 г/дм по MgS0 4 ;

Determination of the individual threshold gradient of taste perception. The Threshold Taste Difference is the minimum difference in flavor concentrations that the examiner is able to detect. It is determined in solutions with a mild, but well recognizable taste. The absolute value of the threshold difference depends on the concentrations of the solution, so the taste sensitivity of the expert should be assessed on an individual basis.

threshold taste gradient on model solutions (table). For example, 1% glucose solution is easy to distinguish from 2%, 20% from 21% is almost impossible. In both solutions, the concentration difference is 1%, but in the first case the concentration gradient is 2.0, in the second - 1.05.

Concentration of model solutions (in g / dm 3) to determine the individual threshold taste gradient

To find the threshold taste gradient, the expert is offered the method of triangular comparisons to detect an experimental sample against the background of reference solutions. The order of supplying solutions is the same as in determining the detection thresholds for the main types of taste.

Zero solutions are solutions of sucrose, sodium chloride, tartaric acid and magnesium sulphate of background concentration. The threshold gradient of the subjects should be:

The individual taste threshold gradient (ITG) characterizes the ability to detect changes in the taste of the test product.

Taste memory assessment. The stability of taste and smell sensations (sensory memory) is one of the most valuable qualities of a taster. Taste memory is assessed by the ability to determine the intensity and quality

taste sensations. A candidate for organoleptic analysts is offered to try 6-7 solutions and is asked to arrange them in order of increasing concentration of the flavoring substance. A similar task is to determine two identical samples from seven solutions of different concentrations. The test solutions should differ by more than the evaluator's individual threshold taste gradient. The concentration gradient of the test solutions is found by the formula 2IPG - 1. For example, if the individual threshold gradient of the estimator is 1.3, the test gradient will be equal to 2x1.3-1=1.6.

In order to determine the stability of taste sensations, the appraiser gets acquainted with the taste of solutions of 8-10 substances. Then they give three samples of the previous series, which the subject must identify. The standard series is made up of substances whose taste is related to wine (in%): tannin - 0.2, citric acid - 0.5, acetic acid - 0.2, glucose - 2, succinic acid - 0.1, tartaric acid -1, diethyl ester of tartaric acid - 0.2, lactic acid - 0.03, sodium sulfide - 0.1. When training taste memory, test tasks can be complicated by a decrease in the concentration gradient of solutions and an increase in the number of substances offered for identification.

TASTE AND SMELL

X. Altner, I. Beckh

13.1. Characteristics of chemical sensations

The sensations of taste and smell are due to the selective and highly sensitive response of specialized sensory cells to the presence of molecules of certain compounds. More broadly, specific responses to chemicals, such as hormones or neurotransmitters, are characteristic of many cells and tissues. However, gustatory and olfactory sensory cells act as exteroceptors; their reactions provide important information about external stimuli, processed by special areas of the brain, which are responsible for the corresponding sensations. Other chemoreceptor cells serve as interoceptors that determine, for example, the level of CO 2 (Sec. 21.6).

Taste and smell can be characterized and distinguished based on morphological and physiological criteria. The differences between these two types of sensations are most obvious when comparing the types (qualities) of stimuli adequate for them (Table 13.1). Other characteristics, such as sensitivity to stimuli or the physical state of the latter, although generally not the same, may overlap.

Compared to other senses, taste and smell are significantly more adaptable (cf. Figure 8.5). With prolonged exposure to a stimulus, excitation in the afferent pathways is noticeably weakened, and perception is correspondingly weakened; for example, already very quickly in an environment, even with a strong smell, we cease to feel it. Equally characteristic of chemical sensations and high sensitivity to certain stimuli. At the same time, the range of distinguishable stimulation intensities is relatively small (1:500), and the discrimination threshold is high. Exponent in Stevens Power Functionψ = k(φ - φо)ais 0.4–0.6 for odor and about 1 for gustatory stimuli (cf. Fig. 8.14).

Primary processes and chemical specificity .

The first event during stimulation of chemoreceptors is, according to modern concepts, a chemical interaction based on the weak binding of an adequate molecule to receptor protein. Proteins with enzymatic properties, substrate

the specificity and kinetic features of which are the same as those of the receptors themselves. The subsequent events leading to the electrical response of the cell membrane are unknown. Each receptor cell reacts highly selectively to a specific group of substances. The slightest change in the structure of a molecule can change the nature of its perception or make it an inadequate stimulus. The stimulatory effectiveness of a compound is probably most significantly dependent on its size (eg, chain length) and the internal distribution of electrical charges (ie, the arrangement of functional groups). However, the fact that in many cases molecules of substances that differ greatly in chemical structure evoke the same olfactory sensations has not yet been explained. For example, the three substances below, despite their structural differences, have the same musky smell (see. Beats in ).

It has been suggested that chemoreceptors contain receptor centers. specific to certain groups of substances. This point of view is confirmed by cases of partial anosmia, i.e., insensitivity to the smell of some very close chemical compounds. Similarly, the selective effect of certain drugs on the organ of taste can be interpreted. Application to the tongue of potassium gymnemate (a substance isolated from an Indian plantGymnema silvestre) leads to the loss of only the perception of sweet - sugar causes a feeling of sand in the mouth. Protein found in the fruit of a West African plantsynsepalium dulcificum, changes the sour taste to sweet, so that the lemon is perceived as an orange (see. kurihara v ). The application of cocaine to the tongue causes a progressive loss of all four types of taste sensations: bitter, sweet, salty, and finally sour.

Table 13.1.Classification and characteristics of chemical feelings

13.2. Taste

Receptors and neurons

In adults sensory taste cells located on the surface of the tongue. Together with supporting cells, they form groups of 40–60 in the epithelium of its papillae. elements - taste buds(Fig. 13.1). Large papillae surrounded by a roller at the base of the tongue contain up to 200 taste buds each; in smaller mushroom-shaped and foliate papillae on its anterior and lateral surfaces, there are only a few of them. In total, an adult has several thousand taste buds. glands, located between the papillae, secrete a fluid that bathes the taste buds. The distal parts of receptor (sensory) cells sensitive to stimulation form microvilli, leaving the common chamber, which communicates with the external environment through a pore on the surface of the papilla (Fig. 13.1). Stimulant molecules, diffusing through this pore, reach the taste cells (receptors).

Like other secondary sensory cells, gustatory cells generate a receptor potential when stimulated. This excitation is synaptically transmitted afferent fibers

Rice. 13.1.Scheme of a taste bud immersed in the papilla of the tongue; the basal, sensory, supporting cells and afferent fibers of the corresponding cranial nerve are shown

cranial nerves, which conduct it to the brain in the form of impulses. This process involves: tympanic string - branch of the facial nerve(VII), which innervates the anterior and lateral parts of the tongue, and glossopharyngeal nerve(IX), which innervates its posterior part (Fig. 13.2). Branching, each afferent fiber receives signals from receptors of different taste buds.

Rice. 13.2.Diagram of human language. Coloring highlights its innervation by various cranial nerves; contours circled areas of distribution of different types of papillae (1-mushroom-shaped, 2-circumscribed, 3-leaf-shaped). Localization of zones of perception of certain taste qualities is shown by icons

Are replacedtaste cells very quickly; the lifespan of each of them is only about 10 days, after which a new receptor is formed from the basal cell. It establishes a connection with afferent fibers in such a way that their specificity does not change. The mechanism providing such interaction is still not clear (see Fig. Oakley in ).

Cell reactions in fibers . Single taste cell in most cases, it reacts to substances representing different taste qualities, depolarizing or hyperpolarizing them (Fig. 13.3). The amplitude of the receptor potential increases with the concentration of the stimulant. The type and amplitude of the response is also influenced by the environment (Fig. 13.4).

The generator potential causes the corresponding level of excitation of the afferent fibers, forming a reaction called the "taste profile" (Fig. 13.5). Their impulsation depends on the reaction of receptors as follows: depolarization of the latter has an excitatory effect, hyperpolarization has an inhibitory effect.

Many fibers of the IXth pair of cranial nerves are especially responsive to substances with a bitter taste. Fibers of the VII pair are more strongly excited by the action of salty, sweet and sour: some of them react more strongly to sugar than to salt, others to salt than to sugar, etc. These taste-specific features

Rice. 13.3.Intracellular records of receptor potentials of two taste cells (a, b) of the rat tongue. Stimuli: 0.5 mol/l NaCI; 0.02 mol/l quinine hydrochloride; 0.01 mol/l HCI and 0.5 mol/l sucrose. The duration of each stimulus is shown horizontal line(on Sato, Beidler in with changes)

Rice. 13.4. Influence of the environment on the shape and amplitude of intracellular recordings of the receptor potential of a single gustatory cell of the rat tongue stimulated by 0.02 mol/l of quinine hydrochloride. Environment: a - 41.4 mmol/l NaCl; b-distilled water (according to Sato, Beidler in with changes)

Rice. 13.5.Responses of two single fibers of the rat drum string to various substances: 0.1 mol/l NaCI;

0.5 mol/l sucrose; 0.01 n. HCI; 0.02 mol/l quinine hydrochloride (modified)

different groups of afferents provide information about taste quality those. the form of a stimulating molecule, and the general level of excitation of a certain population of them is about stimulus intensity, i.e., the concentration of a given substance.

central neurons. Taste fibers VII and IX pairs of cranial nerves terminate within or in close proximity to single path nuclei ( nucleus solitarius ) medulla oblongata. This nucleus is connected with the medial loop (medial lemniscus) thalamus in his area ventral posteromedial nucleus. Axons of third-order neurons pass through the internal capsule and terminate in postcentral gyruscerebral cortex. V As a result of information processing at the above levels, the number of neurons with highly specific taste sensitivity increases. A number of cortical cells react only to substances with one taste quality. The location of such neurons indicates a high degree of spatial organization of the sense of taste. Other cells in these centers respond not only to taste, but also to thermal and mechanical stimulation of the tongue.

human taste sensitivity

Taste qualities . A person distinguishes four main taste qualities: sweet, sour, bitter and salty, which are quite well characterized by substances typical of them (Table 13.2). The taste of sweet is associated mainly with natural carbohydrates such as sucrose and glucose; sodium chloride-salty; other salts such as KCI are perceived as salty and bitter at the same time. Such mixed feelings characteristic of many natural taste stimuli and correspond to the nature of their components. For example, an orange is sweet and sour, and a grapefruit

Table 13.2.Substances with a characteristic taste and the effectiveness of their effects on humans ( Pfaffmann in )

sour-sweet-bitter. Acids taste sour; many plant alkaloids are bitter.

On the surface of the tongue, one can distinguish zones of specific sensitivity. Bitter taste is perceived mainly basis language; other taste qualities affect it side surfaces and tip, moreover, these zones overlap (Fig. 13.2).

Between chemical properties substances and taste there is no single correlation. For example, not only sugars, but also lead salts are sweet, and artificial sugar substitutes such as saccharin have the sweetest taste. Moreover, perceived quality substance depends on concentration. Table salt at low concentration appears sweet and only becomes purely salty when it is increased. Sensitivity to bitter substances is significantly higher. Since they are often poisonous, this feature of them warns us against danger, even if their concentration in water or food is very low. Strong bitter stimuli easily cause vomit or invitations to her.Emotional Components taste sensations vary widely depending on the state of the body. For example, a person who is deficient in salt finds the taste acceptable even if the salt concentration in food is so high that a normal person would refuse to eat.

The taste sensations are obviously very similar. in all mammals. Behavioral experiments have shown that various animals distinguish the same taste qualities as humans. However, registration of the activity of individual nerve fibers also revealed some abilities that are absent in humans. For example, cats are found "water fibers" either responding only to water stimulation or exhibiting a taste profile that includes water as an effective stimulus (see fig. Sato in ).

biological significance . The biological role of taste sensations lies not only in checking the edibility of food(see above); they also affect the digestion process. Connections with vegetative efferents allow taste sensations to influence the secretion of the digestive glands, not only on its intensity, but also on its composition, depending, for example, on whether sweet or salty substances predominate in food.

With agethe ability to distinguish taste is reduced. Consumption of biologically active substances such as caffeine and heavy smoking also lead to this.

13.3. Smell

The surface of the nasal mucosa is enlarged due to the turbinates-ridges protruding from the sides into the lumen of the nasal cavity. olfactory area, containing most of the sensory cells,

Rice. 13.6.Scheme of the cavities of the human nasopharynx (sagittal section). The olfactory region is limited by the upper and middle shells. Areas innervated by the trigeminal (V), glossopharyngeal (IX), and vagus (X) nerves are shown.

here it is limited to the superior nasal concha, although the middle one also has small islands of olfactory epithelium (Fig. 13.6).

Receptors

The olfactory receptor is the primary bipolar sensory cell, from which two processes extend: on top is a dendrite that carries cilia, from the base of the axon. Cilia, whose internal structure is different from those of ordinary kinocilia, are immersed in a layer of mucus covering the olfactory epithelium and are not able to actively move. Odorants brought in by the inhaled air come into contact with their membrane, the most likely site of interaction between the stimulatory molecule and the receptor. Axons heading to the olfactory bulb are combined into bundles ( fila olfactoria ). In the entire nasal mucosa there are, in addition, free endings trigeminal nerve, and some of them also react to smells. In the pharynx, olfactory stimuli are able to excite the fibers of the glossopharyngeal and vagus nerves (Fig. 13.6). A layer of mucus covering the olfactory epithelium prevents it from drying out and is constantly renewed by secretion and redistribution by kinocilia.

Molecules of odorous substances enter to receptors (sensory cells) periodically: during inspiration through the nostrils and, to a lesser extent, from the oral cavity, diffusing through the choanae. Thus, while eating, we have mixed sensations in which the taste and smell of food are combined.

Rice. 13.7.Simultaneous electroolfactogram recording (Red line) and action potentials of a single receptor in the frog olfactory epithelium upon stimulation with nitrobenzene. Stimulus duration (black line)–1 s ( Gesteland in )

Sniffing, a characteristic behavior of many mammals, greatly increases the flow of air to the olfactory mucosa and, consequently, the concentration of stimulating molecules in it.

In total, a person has about 10 7 receptors in the olfactory region with an area of ​​​​approximately 10 cm 2. In other vertebrates, there are much more of them (in a German shepherd, for example, 2.2–10 8). The olfactory cells, like the gustatory ones, are constantly being replaced, and because of this, apparently, not all of them function at the same time.

Electrodes placed on the olfactory epithelium of vertebrates, when exposed to odor, register slow potentials of complex shape with an amplitude of several millivolts. These electroolfactograms(EOG, Fig. 13.7, see Ottoson c), as well as electroretinograms (ERGs), reflect the total activity of many cells, therefore they do not provide information about the properties of individual receptors. Record Activity single receptor in the olfactory mucosa of vertebrates was possible only by chance (Fig. 13.7). It has been shown that the spontaneous activity of these cells is very low (several impulses per second), and each of them reacts to many substances. As with the flavor profile, one can build range of responses single olfactory receptor (see Gesfeland in ).

Types of odors

A person is able to distinguish the smell of thousands of different substances. Olfactory sensations can be classified on the basis of their certain similarities, identifying certain types, or quality, smell. However, this is much more difficult to do than in the case of taste sensations. The vagueness of the categories is also evident in the fact that the classifications proposed by different authors are not the same. The correlation between chemical structure and odor quality is even smaller than in the case of gustatory stimuli. Tab. 13.3 shows that odor classes are usually named after their natural

Table 13.3.Distinctive characteristics of odor classes ( Amoor, Skramlik)

sources or typical substances; each category can also be characterized by a "standard" source.

The neurophysiological basis for assigning odors to a particular class has not yet been discovered. The point of view, according to which groups that combine substances similar in smell differ from each other in some way, is confirmed by cases of partial impairment of smell (partial anosmia). With such defects (at least some of them genetic in nature), the threshold for the perception of certain olfactory stimuli is increased. Moreover, it often changes for several substances, which, as a rule, belong to the same class of odors. Experimental data used to classify odors can be obtained by analyzing cross adaptation. It lies in the fact that when prolonged exposure to any smell causes an increase in the threshold of its perception, the sensitivity to the smell of some other substances also decreases (Fig. 13.8). By studying quantitatively such mutual changes in thresholds, it is possible to construct a diagram of cross-adaptive relationships (Fig. 13.9). However, this is not enough for an unambiguous and detailed classification of many odorous substances according to the sensations they cause.

When interpreting the features of the human sense of smell, it should be borne in mind that endings are also sensitive to odorous substances. trigeminal nerve in the nasal mucosa, and glossopharyngeal and vagus nerve in the throat. All of them are involved in the formation of the olfactory sensation (Fig. 13.6). Their role, which is in no way connected with the olfactory nerve, is also preserved in case of violations of the function of the olfactory epithelium due, for example, to infection (flu), tumors (and related brain operations) or traumatic brain injuries. In such cases, united by the term hyposmia, the threshold of perception is significantly higher than normal, but the ability to distinguish smells is reduced only slightly. In pituitary hypogonadism (Kalman's syndrome), the sense of smell is provided exclusively by these cranial nerves, since aplasia of the olfactory bulbs occurs in this congenital disease. Harmful thermal and chemical effects can cause reversible or irreversible acute or chronic hyposmia or anosmia, depending on the nature and method of exposure. Finally, sensitivity to smells decreases with age.

Sensitivity; coding

The human sense of smell is very sensitive, although it is known that in some animals this apparatus is even more perfect. In table. 13.4 shows the concentrations of two odorous substances sufficient to cause the corresponding sensations in a person. Under the action of very small amounts of them, the resulting sensation is nonspecific; only after exceeding a certain threshold level, the smell is not only detected, but also recognized. For example, skatole smells quite acceptable at low concentrations; at higher levels, it is repulsive. Thus, it is necessary to distinguish detection threshold and recognition threshold smell.

Such thresholds, determined by the responses of the subjects or the behavioral reactions of animals, do not allow one to establish sensitivity of a single sensory cell(receptor). However, knowing the spatial extent of the human olfactory organ and the number of receptors in its composition, one can also calculate their sensitivity. Such calculations show that a single sensory cell depolarizes and generates an action potential in response to one or at most a few odorant molecules. Of course, a behavioral response requires the activation of a significant number of receptors; exceeding a certain critical level of the signal-to-noise ratio in the afferent fibers.

Coding.The encoding of olfactory stimuli by receptors can only be described as a first approximation. First, the individual sensory cell is capable of responding to many different odorants. Secondly,

Rice. 13.8.Increasing the intensity of sensation with increasing stimulation intensity (propanol) without adaptation (black straight line) and after adaptation to pentanol (red curve with black triangles) ( Cain, Engen in with changes)

Rice. 13.9.Cross-adaptive relationships of seven odorous substances: 1-citral, 2-cyclopentanone, 3-benzyl acetate, 4-safrole, 5-m-xylene, 6-methyl salicylate, 7-butyl acetate. Reciprocal interactions are usually unequal. The degree of increase in the perception threshold is indicated as follows: black lines are very big; red solid lines are big; red dashed lines—moderate; red dotted line - weak(as amended)

Table 13.4.Detection threshold for butyric acid and butyl mercaptan odors ( Neuhaus, Stuiver)

different olfactory receptors (as well as taste receptors) have overlapping response profiles. Thus, each odorous substance specifically excites a whole population of sensory cells; while the concentration of the substance is reflected in the overall level of excitation.

Central processing of olfactory information

Olfactory bulb . Histologically, the olfactory bulb is divided into several layers, characterized by cells of a specific shape, from which processes of a certain type extend with characteristic connections between them. The main features of information processing here are as follows: significant convergence sensory cells on the mitral; pronounced inhibitory mechanisms and efferent control input impulse. In the glomerular (glomerular) layer, the axons of approximately 1000 receptors terminate on the primary dendrites of one mitral cell(Fig. 13.10). These dendrites also form reciprocal dendrodendritic synapses with periglomerular cells. Mitral-periglomerular contacts-excitatory, opposite in direction-inhibitory. The axons of the periglomerular cells terminate on the dendrites of the mitral cells of the neighboring glomerulus. This organization allows you to modulate the local dendritic response, providing auto-braking and inhibition of surrounding cells. Grain Cells also form dendrodendritic synapses with mitral cells (in this case, with their secondary deidrites) and thereby influence their generation of impulses. Entrances on mitral cells are also inhibitory; reciprocal contacts are involved in autoinhibition. Finally, granule cells form synapses with collaterals of mitral cells, as well as with efferent (bulbopetal) axons of various origins. Some of these centrifugal fibers come from the contralateral bulb through the anterior commissure (commissure).

A feature of the inhibition caused by granule cells devoid of axons is that, in contrast to typical Renshaw inhibition, they can be activated partially, i.e. with a spatial gradient. This

Rice. 13.10.Diagram of neuronal connections in the olfactory bulb. In the glomeruli (glomeruli), the axons of the olfactory receptors terminate on the primary dendrites ( D 1) mitral cells. Periglomerular cells and granule cells form reciprocal synapses with primary and secondary ( D 2) dendrites of mitral cells. K-collaterals. The direction of synaptic transmission is shown by arrows: excitatory influences - black, brake - red(on with generalizations and changes)

the picture of very complex interactions is quite comparable to that known in the retina, although information processing is based on a different principle of cellular organization. All of the above is just a rough outline of what happens in the olfactory bulb. In addition to mitral, secondary neurons also include a variety of fascicular cells, which differ in their projections and mediators.

Central communications . axons mitral cells form lateral olfactory tract, bound for prepiriform cortex and pyriform share. Synapses with higher-order neurons provide communication with hippocampus and, through the amygdala, with vegetative nuclei hypothalamus. Neurons responding to olfactory stimuli have also been found in reticular formation midbrain and orbitofrontal cortex.

The influence of smell on other functional systems . Direct connection to the limbic system (see section 16.6) explains the pronounced emotional component olfactory sensations. Smells can cause pleasure or disgust (hedonic components), influencing the affective state of the organism accordingly. In addition, the importance of olfactory stimuli in regulation of sexual behavior although the results of animal experiments, especially experiments on the blockade of smell in rodents, cannot be directly transferred to humans. It has also been shown in animals that the responses of neurons in the olfactory tract can be altered by injection of testosterone. Thus, sex hormones also affect their arousal.

Functional disorders . In addition to hyposmia and anosmia, there are incorrect perception of smell (iarosmia) and olfactory sensations in the absence of odorous substances (olfactory hallucinations). The reasons for these disorders are varied. For example, they can occur with allergic rhinitis and head trauma. Olfactory hallucinations of an unpleasant nature (cacosmia) are observed mainly in schizophrenia.

13.4. Literature

Tutorials and guides

1. Beidler L.M.(Ed.). chemical senses. Part 1. Olfaction. Part 2. Taste. Handbook of Sensory Physiology, Vol. IV, Berlin-Heidelberg-New York, Springer, 1971.

2. PfaffD.(Ed.). Taste. Olfaction and Central Nervous System. New York, Rockefeller University Press, 1985.

Original articles and reviews

3. Breipohl W.(Ed.). Olfaction and Endocrine Regulation, London, IRL Press, 1982.

4. Denton D.A., Coghlan J.P.(Eds.). Olfaction and Taste, Vol. V, New York, Academic Press, 1975.

5. Hayushi T. (Ed.). Olfaction and Taste, Vol. II, Oxford-London New York-Paris, Pergamon Press, 1967.

6. Kare M. R., Mailer 0.(Eds.). The Chemical Senses and Nutrition, New York–San Francisco London, Academic Press, 1977.

7. Coster E. Adaptation and Cross Adaptation in Olfaction, Rotterdam, Bronder, 1971.

8. Le Magnen J., Mac Lead P.(Eds.). Olfaction and Taste., Vol. VI, London–Washington DC, IRL Press, 1977.

9. Norris D.M.(Ed.). Perception of Behavioral Chemicals, Amsterdam–New York–Oxford, Elsevier/North Holland, 1981.

10. pfaffman WITH. (Ed.). Olfaction and Taste, Vol. Ill, New York, Rockefeller University Press, 1969.

11. Sato T. Receptor potential in rat taste cells. In: Autrum H., Ottoson D., PerlE.R., Schmidt R.F., Shimazu H., Willis W.D.(Eds.). Progress in Sensory Physiology, Vol. 6, p. 1–37, Berlin–Heidelberg–New York–Tokyo, Springer, 1986.

12. Schneider D.(Ed.). Olfaction and Taste, Vol. IV, Stuttgart, Wiss, Verlagsges, 1972.

13. Shepherd G.M. Synaptic organization of the mammalian olfactory bulb. physiol. Rev. 52, 864 (1972).

14. Van der Starre H.(Ed.). Olfaction and Taste. Vol. VII, London–Washington DC, IRL Press, 1980.

15. Zotterman Y.(Ed.). Olfaction and Taste. Vol. I. Oxford-London-New York Paris, Pergamon Press, 1963.

16. Chemical Senses. London. IRL Press (Published in regular installments).