The main types of gustatory sensitivities. Gustatory sensory system
Subject table of contents "Vestibular sensory system. Taste. Taste sensitivity. Olfactory sensory system. Smell (odors). Classification of odors.":1. Vestibular sensory system. Function of the vestibular system. Vestibular apparatus. Bone labyrinth. Membranous labyrinth. Otoliths.
2. Hair cells. Properties of the receptor cells of the vestibular apparatus. Stereocilia. Kinocilius.
3. Otolith apparatus. Otolithic organ. Adequate stimuli for the receptors of the otolith organs.
4. Semicircular canals. Adequate stimuli for the receptors of the semicircular canals.
5. The central part of the vestibular system. Vestibular nuclei. Kinetoses.
6. Taste. Gustatory sensitivity. Gustatory sensory system. Taste reception. Taste time.
8. Central department of the gustatory system. Pathways of taste sensitivity. Cores of taste.
9. Taste perception. Olfactory sensory system. Macrosmatics. Microsmatics.
10. Smell (s). Odor classification. Stereochemical theory of odors.
Membrane of microvilli of taste cells contains specific sites (receptors) intended for binding chemical molecules dissolved in the liquid medium of the oral cavity. There are four varieties of taste sensations, or four taste modalities: sweet, sour, salty, and bitter. Strict dependence between chemical nature of the substance and no taste: for example, not only sugars have a sweet taste, but also some inorganic compounds (lead, beryllium salts), and the sweetest substance is saccharin, which cannot be absorbed by the body. Most taste cells are polymodal, that is, they can respond to stimuli from all four taste modalities.
Joining to specific receptors molecules with a sweet taste activates the system of secondary messengers adenylate cyclase - cyclic adenosine monophosphate, which close the membrane channels of potassium ions, and therefore the membrane of the receptor cell is depolarized. Substances with a bitter taste activate one of two systems of secondary mediators: 1) phospholipase C - inositol-3-phosphate, which leads to the release of calcium ions from the intracellular depot with subsequent release of the mediator from the receptor cell; 2) the specific G-protein gastducin, which regulates the intracellular concentration of cAMP, which controls the cation channels of the membrane and this determines the emergence of the receptor potential. The action on the receptors of molecules with a salty taste is accompanied by the opening of gated sodium channels and depolarization of the taste cell. Substances with a sour taste close the membrane channels for potassium ions, which leads to depolarization of the receptor cell.
The magnitude of the receptor potential depends on palatability and concentration of the chemical acting on the cell. The emergence of a receptor potential leads to the release of a neurotransmitter by the taste cell, which acts through the synapse on the afferent fiber of the primary sensory neuron, in which the frequency of action potentials increases 40-50 ms after the onset of the stimulus. Nerve impulses arising in afferent fibers are conducted to the nuclei of single bundles of the medulla oblongata. With an increase in the concentration of the active substance, the total number of responsive sensory fibers increases due to the involvement of high-threshold afferents in the transmission of information from receptors.
Taste sensitivity
Gustatory thresholds are detected by alternately applying solutions of substances with different taste qualities to the surface of the tongue (Table 17.4). The absolute threshold of sensitivity is the appearance of a certain taste sensation that differs from the taste of distilled water. Taste the same substance can be perceived differently depending on its concentration in solution; for example, at low concentrations of sodium chloride, it tastes sweet, and at higher concentrations, salty. The maximum ability to distinguish between the concentration of solutions of the same substance and, accordingly, the lowest differential threshold of taste sensitivity is characteristic for the middle range of concentrations, and at high concentrations of the substance, the differential threshold increases.
Table 17.4. Absolute thresholds for the perception of substances with a characteristic taste
Absolute gustatory thresholds individually differ, but the overwhelming majority of people have the lowest detection threshold for substances with a bitter taste. This feature of perception arose in evolution, it contributes to the rejection of the use in food of substances of bitter taste, to which the alkaloids of many poisonous plants belong. Flavoring thresholds differ in the same person depending on his need for certain substances, they increase due to prolonged use of substances with characteristic taste(for example, sweets or pickles) or smoking, alcohol consumption, burning drinks. Different areas of the tongue differ in taste sensitivity to various substances, which is due to the peculiarities of the distribution of taste buds. The tip of the tongue is more sensitive to sweetness than other areas, the sides of the tongue to sour and salty, and the root of the tongue to bitter. Taste sensations in most cases are multimodal and are based not only on the selective chemical sensitivity of taste receptor cells, but also on food irritation. thermoreceptors and mechanoreceptors of the oral cavity, as well as the effect of volatile food components on olfactory receptors.
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Department of Physiology
Physiology of taste
Introduction
1. Morphology of the organs of taste; subjective physiology of taste. Orientation and structure of taste buds
2. Central connections
3. Basic taste sensations
4. Intensity of sensations
5. Objective physiology of taste
6. Primary process
7. The role of gustatory sensitivity
Literature
Introduction
Man and animal continuously receive information about the endless variety of changes that occur in the external and internal environment. This is due to the presence of specialized structures in the body, which are called analyzers (sensory systems).
Analyzers are understood as a set of formations that ensure the perception of stimulus energy, its transformation into specific processes of excitation, the conduction of this excitation into the structures of the central nervous system and to the cells of the cortex, analysis and synthesis of this excitation by specific zones of the cortex, followed by the formation of sensation.
The concept of analyzers was introduced into physiology by I.P. Pavlov in connection with the doctrine of higher nervous activity. Each analyzer consists of three sections:
The peripheral or receptor section, which perceives the energy of the stimulus and transforms it into a specific process of excitation.
The conduction department, represented by afferent nerves and subcortical centers, carries out the transmission of the arisen excitement to the cerebral cortex.
The central or cortical part of the analyzer, represented by the corresponding areas of the cerebral cortex, where the higher analysis and synthesis of excitations and the formation of the corresponding sensation are carried out.
The role of analyzers in the formation of adaptive reactions is extremely large and diverse. According to the concept of the functional system of P.K. Anokhin, the formation of any adaptive reaction is carried out in several stages. Analyzers are directly involved in the formation of all stages of the functional system. They are suppliers of afferent parcels of a certain modality and various functional purposes, moreover, the same afferentation can be situational, starting, reverse and indicative, depending on the stage of formation of adaptive activity.
taste physiology analyzer organ
1. Morphology of the organs of taste; subjective physiology of taste.Orientation and structure of taste buds
The tongue in humans is covered with a mucous membrane, the folds of which in many places form small protuberances in the form of pegs, called papillae.
These three types are distributed in different ways. Only mushroom papillae are scattered over the entire surface. Grooved papillae, of which a person has only 7-12, from above have the appearance of round formations 1-3 mm in diameter; they are located in a limited area across the dorsum of the tongue at its root. The third type, leaf-shaped papillae, form tightly spaced folds along the posterior edges of the tongue. They are well developed in children, but much less pronounced and less numerous in adults.
The filiform papillae that occupy the rest of the tongue are not shown in Fig. 1 because they lack taste buds. The name "kidney" refers to the shape of these organs (Fig. 2). Their position on the papillae varies; in the case of grooved and leaf-shaped papillae, many taste buds are embedded in the side walls, but there are none at the apex. In mushroom papillae, taste buds are limited by the surface of the mushroom cap, which can be up to 1 mm in diameter.
The individual taste bud is about 70 µm in height and about 40 µm in diameter. In total, a person has about 2000 taste buds, of which about half are on grooved papillae. Each taste bud contains 40-60 individual cells.
Serous glands are immersed in the connective tissue under the grooved and leaf-shaped papillae, the ducts of which open into the recesses at the base of the papilla, their secret serves to wash away food particles and microorganisms. In addition, it lowers the concentration of the stimulant near the taste buds.
Inside the taste buds, three types of cells are distinguished: sensory, supporting, and basal (Fig. 2). Water-soluble substances that fall on the surface of the tongue diffuse through the pore into the liquid-filled space above the taste bud; here they come into contact with the membranes of the microvilli, which form the outer ends of the sensory cells. Taste receptors are secondary sensory cells without axons that conduct impulses in a central direction. Their responses are transmitted by afferent fibers that form synapses near the bases of sensory cells. In fig. 2 shows only two fibers, but in reality about 50 fibers enter and branch into each taste bud.
The lifespan of sensory cells in taste buds is short; there is a continuous change. On average, one sensory cell is replaced by a new one within 10 days. The change of cells can be traced by marking their nuclei with 3H-thymidine and determining the number of labeled nuclei preserved after some time. Lost sensory cells are replaced by new ones that are formed from basal cells. With this change, synapses between afferent fibers and old cells should be interrupted and new synapses should arise. In connection with this rearrangement, many interesting questions arise, especially if we take into account the fact that sensory cells differ in their sensitivity to different stimuli. Thus, a change in sensory cells can lead to a change in the "taste profile" - a characteristic form of responses in afferent fibers, which will be discussed in the next section.
2. Central connections
Afferent fibers conducting responses from clusters of taste buds are distributed along two cranial nerves - the facial (VII) and glossopharyngeal (IX). This division usually corresponds to the regions of the tongue that are supplied with these fibers. So, the fibers from the grooved and leaf-shaped papillae go mainly as part of the glossopharyngeal nerve, and the fibers from the mushroom papillae in the front of the tongue enter the drum string (chorda tympani), a branch of the facial nerve. Children have additional taste organs in the epithelium of the soft palate and the posterior wall of the pharynx to the larynx; they are innervated mainly by the vagus nerve (X).
In the brain, taste fibers on each side combine to form a solitary tract. It ends in the medulla oblongata, in the nucleus of the solitary tract, where afferent fibers form synapses with second-order neurons. The axons of these neurons go to the ventral thalamus as part of the medial lemniscus. The third set of neurons connects this area with the cerebral cortex. The gustatory zones of the cortex are located in the lateral part of the postientral gyrus.
3. Basic taste sensations
Under normal conditions, such as eating, the oral mucosa is exposed to complex stimuli that include several modalities. Due to the fact that the oral cavity communicates with the nasal cavity, odorous substances can reach the olfactory receptors in the nose and cause other sensations. In addition, the mucous membrane of the mouth and tongue contains thermoreceptors, mechanoreceptors, and pain fibers, which are also stimulated. What is commonly referred to as "taste" is actually a multimodal sensation in which sensations of smell, warmth or cold, pressure and possibly even pain are superimposed on the actual taste sensations.
There are four distinct basic taste sensations: sweet, sour, salty, and bitter.
The detection thresholds for different qualities are at different concentrations. The threshold concentration of quinine sulfate (8 μmol / L, or 0.006 g / L) is a good example that bitter tasting substances are found at very low concentrations. The detection threshold for saccharin is 23 μmol / L (0.0055 g / L), for grape sugar - 0.08 mol / L, and for cane sugar - 0.01 mol / L (14.41 and 3.42 g, respectively) / l). These data are representative, and they show that the thresholds for mono- and disaccharides are significantly higher than for synthetic sweets. The thresholds for acetic acid (0.18 mol / L, or 0.108 g / L) and table salt (0.01 mol / L, or 0.585 g / L) illustrate the general rule that the thresholds for sour and salty are about the same order of magnitude. as for the above saccharides. Acid thresholds roughly reflect the degree of acid dissociation. Comparison of the thresholds for grape and cane sugar suggests that the grape sugar solution must be more concentrated than the cane sugar solution in order for them to be equally sweet. Experimental verification of solutions of different above-threshold concentrations corresponds to this difference.
But the usefulness of such accurate cut-off data is limited because, for most substances, the cut-off levels are subject to significant individual variability. It would be more reasonable to talk about the range of threshold values
4. Intensity of sensations
A simple comparison of different solutions shows that the intensity of the mouthfeel depends on the concentration of the substance. When determining the thresholds, it was found that the effect of diluting the stimulant solution can be compensated for by stimulating a larger surface of the tongue, i.e. a greater number of receptors This is probably due to spatial summation. In the threshold region, there is an input relationship between the concentration and the duration of the stimulus. In addition, it should be remembered that the sense of taste is subject to a certain adaptation - with prolonged action of the stimulus, the intensity of the sensation decreases. Another factor is the secretion of the serous glands, which dilutes the substance acting on the taste buds and thus influences the intensity of the sensation.
Testing of a number of dilutions of saline solutions in the near-threshold region in many cases shows that sensation can change its quality depending on concentration. Table salt solutions 0.02-0.03 mol / l have a sweet taste, and at a concentration of 0.04 mol / l or more, they are salty. This shift in quality can probably be understood from the fact that taste fibers have a wide range of sensitivities within each quality.
Different areas of the language in humans vary in sensitivity to four basic qualities. The tip of the tongue is especially sensitive to sweet substances; the middle portions of the edges respond best to sour stimuli. Salt stimuli are most effective in the region of the tongue edge, which partially overlaps the first two. Bitter substances act most strongly on receptors near the root of the tongue, in the region of the grooved papillae. Therefore, damage to the glossopharyngeal nerve reduces the ability to detect bitterness, and after blockade of conduction in the facial nerve, only they are found.
5. Objective physiology of taste
The ability to discriminate tastes depends on the specificity of receptor molecules in the membranes of sensory cells. Microelectrodes can be used to register the activity of both individual sensory cells and afferent fibers. Such records show that neither the receptors themselves nor the fibers going to the central nervous system give qualitatively specific responses; incentives in more than one category are generally effective. Obviously, each fiber responds to stimuli of several categories, but when considering different gradations of sensitivity, differences are revealed. In other words, stimulation with a solution of a substance at a certain concentration activates different fibers to varying degrees. The arousal pattern typical of each individual fiber in response to a range of substances is called the flavor profile. The fibers closest to qualitative specificity are those that respond to sugar solutions by increasing the discharge frequency. Comparative studies have shown that such relatively specific fibers are especially characteristic of monkeys.
Registration of the activity of individual sensory cells showed that they have a gradual relative specificity. The responses of the fibers coming from these cells, in this respect, reflect the responses of the cells. But afferent fibers branch out in taste buds, so that each fiber receives excitation from many sensory cells, which, presumably, differ in the degree of specificity. In addition, it was found that sensory cells in different papillae form synapses with collaterals from one afferent fiber. This means that taste fibers receive inputs from sensory cells distributed over large areas of the tongue. These areas are called receptive fields. The situation with receptive fields is complicated by the fact that individual sensory cells can receive innervation from several different fibers.
The gradual relative specificity of taste fibers is created by 1) the gradual relative specificity of sensory cells and 2) the branching of taste fibers that creates receptive fields. The frequency of impulses in a single afferent fiber therefore varies with both the quality of the stimulus and its concentration. Of course, the extent to which the stimulated area covers the fiber's receptive field is also an important factor. The obvious takeaway with regard to stimulus coding is that the activity of a single fiber cannot provide unambiguous information about quality or concentration. Only a comparison of the level of arousal in several fibers can reveal characteristic distributions (patterns) of activity that say something about the quality of the stimulus. Provided the quality is known, the frequency of pulsing in each individual fiber can serve as a measure of the concentration of the stimulant. Distinctive features of a substance are therefore encoded in such a way that a complex but characteristic pattern of excitation is created by the simultaneous but different responses of many neurons.
6. Primary process
The condition for excitation of the taste receptor is the interaction between the molecules of the stimulating substance and specially differentiated points in the membrane of the sensory cell, where the receptor molecules lie. This interaction is called the primary process; it is believed to begin with the adsorption of the stimulus molecule. It is believed that when this happens, the receptor-probably protein-molecule changes its structure. This conformational change in the receptor molecule leads in turn to a local change in the permeability of the cell membrane. This cellular "amplifying mechanism" could be the reason for the generation of the receptor potential.
Evidence for the existence of specific receptor molecules includes the observation that certain plant substances and drugs, such as cocaine and hymnic acid (obtained from the Indian plant Gymnema sylvestre), selectively block some taste sensations. Obviously, this acid binds to receptor molecules for sweet substances, since its application makes such substances tasteless. The primary process in the membranes of taste sensory cells has not yet been fully explained, but according to the working hypothesis, it is similar to the process in cholinergic synapses, where special molecules change permeability at specific points in the membrane.
7. The Role of Gustatory Sensitivity
The taste buds on the tongue respond to stimuli located in the mouth. In other words, gustatory 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 distant distance. In water, flavoring substances are transported by diffusion and convection from very distant sources to the flavoring bulbs, which can be dispersed over the entire surface of the fish's body.
In addition to its role in orientation at close range, a person's sense of taste has an important function, triggering a number of reflexes. For example, washing the tongue with secretion from the serous glands is controlled by a reflex, which is under the influence of taste buds. Salivary secretion is also triggered by reflexive stimulation of the taste buds. Even the composition of saliva varies depending on the nature of the stimuli acting on the sensory cells, and gustatory stimuli also affect the secretion of gastric juice. Finally, it has been shown that vomiting is caused by the participation of gustatory 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 V. V. Fundamentals of neurophysiology: textbook for university students. - M .: Aspect Press, 2000. p. 277.
4. Shulgovskiy VV Physiology of higher nervous activity with the basics of neurobiology: Textbook for student biol. specialties of universities. - M .: Publishing Center "Academy", 2003. - 464 p.
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Taste is the sensation that occurs when a substance acts on the taste buds of the tongue and oral mucosa. In the course of evolution, taste has evolved as a sensory mechanism that promotes the choice of "good" food, which implies that taste influences our food preferences. In addition, irritation of the taste buds leads to the emergence of numerous innate (unconditioned) reflexes that control the activity of the digestive system. At the same time, depending on the properties of the food, the secret secreted by the digestive glands can significantly change its composition.
Taste receptors are cells that irritate the taste buds. Most of them are located in the language. In addition, taste buds are located on the back of the pharynx, soft palate, and epiglottis. Receptor cells are combined into taste buds (bulbs), and they are collected in three types of papillae - mushroom, groove and leaf-shaped.
Different parts of the tongue are sensitive to taste modalities in different ways. The base of the tongue, where grooved papillae predominate, are most sensitive to bitter, the tip of the tongue (mostly mushroom papillae on it) to sweet, the lateral parts of the tongue (leaf-shaped papillae) to sour and salty.
The taste bud lies in the thickness of the stratified epithelium. It has the shape of an onion and consists of supporting, receptor and basal cells. Each kidney contains several dozen cells. The kidneys do not reach the surface of the mucous membrane and are connected with it through small channels - taste pores. In this case, the receptor cells form microvilli at their apex, which are located in a common chamber directly under the pore. Taste receptors are the shortest living sensory cells in the body. The lifespan of each of them is about 10 days, after which, just as in the case of the olfactory system, a new receptor is formed from the basal cell. An adult has 9-10 thousand taste buds. With age, some of them atrophy.
Taste receptors are secondary. Sensory neurons that conduct gustatory information in the central nervous system are pseudo-unipolar neurons that are part of the ganglia of the facial (VII pair), glossopharyngeal (IX pair) and vagus (X pair) cranial nerves. The peripheral processes of these neurons approach the taste buds, and with sufficiently strong excitation of the receptors, nerve impulses are conducted in the central nervous system. Taste fibers terminate in a sensory nucleus located in the medulla oblongata (solitary tract nucleus). Through this nucleus, communication is maintained with unconditioned reflex centers that carry out the simplest reflexes, for example, salivation, chewing, and swallowing. A bitter taste is a signal for triggering a number of defensive reactions (spitting out, vomiting, etc.).
Most of the axons of the nucleus of the single pathway intersect, rise up to the thalamus (where it ends on the neurons of the posterior ventral nucleus) and then to the cerebral cortex. It has now been found that taste centers are located in the insular lobe of the bark, as well as at the lower end of the central groove (field 43). A number of axons coming from the medulla oblongata end in the hypothalamus. They contribute to the management of the level of food and defensive motivation, the generation of positive and negative emotions, and also determine unconscious food preferences.
There are five main taste modalities: sweet, salty, sour, bitter and umami. The latter modality is denoted by the Japanese word for MSG taste (well-defined meaty taste). When studying their features, solutions of various substances are used, which are drip applied to different parts of the tongue. As a reference sweet substance, glucose is used, acidic - hydrochloric acid, salty - sodium chloride (table salt, NaCl), bitter - quinine. Each receptor cell is most sensitive to a certain gustatory modality, but responds to other types of gustatory stimulation (usually much weaker, i.e. with a higher threshold of reaction).
"Sweet", "bitter" and "umami" molecules interact with membrane receptors, which ultimately leads to the release of a transmitter in synapses between receptor cells and fibers of sensory cells and conduction of nerve impulses in the central nervous system. The mechanism of generation of the receptor potential during the perception of salty and sour tastes differs from the usual principle of chemoreceptors. In "salty" receptor cells, there are open sodium channels. Salty food contains a large amount of Na + ions, so it diffuses (enters) into the taste cells, causing depolarization. It, in turn, leads to the release of the mediator. Sour taste is caused by the high concentration of hydrogen ions (H +) in acidic foods. Entering the receptor cell, they also cause depolarization.
In addition to taste receptors, there are also skin receptors in the oral cavity. Under normal conditions, a holistic taste perception is formed with their participation (determination of the consistency of food, its temperature, etc.). Moreover, through tactile receptors, at first glance, gustatory sensations such as menthol and burning (spicy) are mediated. The olfactory analyzer also contributes to the formation of gustatory perception. When the sense of smell is impaired (for example, during a runny nose), taste is significantly reduced.
Thresholds of sensitivity of taste buds are very individual for different people (some of the differences are genetically set) and can vary depending on many conditions. For example, the threshold for sodium chloride (table salt) decreases when it is removed from food and increases during pregnancy. The sensation of taste also depends on the concentration of the substance. So, the maximum sweetness is a 20% sugar solution, the maximum salty 10% sodium chloride solution, the maximum acidic 0.2% hydrochloric acid solution, the maximum bitter 0.1% quinine solution. With a further increase in concentration, the taste sensation decreases. Taste sensations also depend on temperature: "sweet" receptors are most sensitive at a food temperature of about 37C, "salty" ones - at about 10C, at 0C taste sensations disappear.
Like all other sensory systems, gustatory is able to adapt to a constantly acting stimulus, and with prolonged excitation of receptors, their threshold increases. Adapting to one of the gustatory sensations often lowers the thresholds for the rest. This phenomenon is called gustatory contrast. For example, after rinsing the mouth with a slightly salted solution, the sensitivity to other taste modalities increases.
The ability to recognize the main types of taste. Testing of sensory sensitivity by recognizing the main types of taste is carried out on model solutions of chemically pure substances:
For the preparation of 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, 35 ml of solution is poured 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. Take a 1-2-minute break between samples, rinsing your mouth with clean water. With seven or more correct answers, the candidate tasters recommend the following test problems to be completed.
Determination of the 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 batch consists of 12 solutions.
Concentration of model solutions (in g / dm 3) to determine individual taste thresholds
The 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 triplet of solutions, two are the solvent, and one is the investigated one. They are served in an ascending sequence, within one triplet, of a random sequence unknown to the subject. For example:
The threshold sensitivity to the main types of taste in organoleptic-analytic candidates should be:
for sweet taste< 7,0 г/дм по сахарозе;
for a 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. Taste Threshold is the smallest difference in flavor concentration that an expert can detect. It is determined in solutions with a mild, but well-recognizable taste. The absolute value of the threshold difference depends on the concentration of the solution, therefore the sensitivity of the taste of an expert should be assessed on an individual basis.
threshold taste gradient on model solutions (table). For example, a 1% glucose solution is easy to distinguish from a 2% solution, and a 20% glucose solution from a 21% solution 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 find an experimental sample against the background of reference solutions. The order of feeding the solutions is the same as when determining the detection thresholds for the main types of taste.
Zero solutions are solutions of sucrose, sodium chloride, tartaric acid and magnesium sulfate of background concentration. The threshold gradient of the subjects should be:
Individual threshold taste gradient (IPG) characterizes the ability to detect changes in the taste of the test product.
Assessment of taste memory. The stability of taste and smell (sensory memory) is one of the most valuable qualities of a taster. Taste memory is assessed by the ability to determine intensity and quality
taste sensations. An organoleptic analyst candidate is offered to try 6-7 solutions and are asked to arrange them in order of increasing concentration of the flavoring agent. A similar task is to determine two identical samples from seven solutions of different concentrations. The test solutions should differ more than the individual taste threshold of the evaluator. The concentration gradient of the test solutions is found by the formula 2IPG - 1. For example, if the individual threshold gradient of the evaluator is 1.3, the test gradient will be 2x1.3-1 = 1.6.
In order to determine the stability of taste sensations, the evaluator gets acquainted with the taste of solutions of 8-10 substances. Then give three samples of the previous series, which the subject must identify. The standard series consists 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 problems can be complicated by a decrease in the concentration gradient of solutions and an increase in the number of substances offered for identification.
Taste qualities.
A person distinguishes four main taste qualities: sweet, sour, bitter and salty,
which are fairly well characterized by their typical substances. The sweet taste 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
are characteristic of many natural gustatory stimuli and correspond to the nature of their components. For example, orange is sweet and sour, and grapefruit is bittersweet and sour. Acids taste sour; many plant alkaloids are bitter. On the surface of the tongue, zones of specific sensitivity can be distinguished.
The bitter taste is perceived mainly by the base of the tongue; other taste qualities affect its lateral surfaces and the tip, and these zones overlap.
Between chemical properties
substance and its taste
there is no one-to-one correlation. For example, not only sugars, but also lead salts are sweet, and artificial sugar substitutes such as saccharin have the sweetest taste. Moreover, the perceived quality of a substance depends on its concentration. Table salt in low concentration appears sweet and becomes purely salty only when it is increased. Sensitivity to bitter substances is significantly higher. Since they are often poisonous, this feature warns us against danger, even if their concentration in water or food is very low. Strong bitter irritants easily induce vomiting or the urge to vomit. Emotional components
taste sensations vary widely depending on the state of the organism. For example, a person who is deficient in salt finds the taste to be acceptable, even if its concentration in food is so high that a normal person would refuse to eat.
Taste sensations are apparently very similar in all mammals. Behavioral experiments have shown that different animals have the same taste characteristics as humans. However, registration of the activity of individual nerve fibers also revealed some abilities that are absent in humans. For example, cats have been found to have "water fibers" that either respond only to irritation with water or exhibit a taste profile that includes water as an effective stimulus.
Biological significance.
The biological role of gustatory senses is not only to test the edibility of food (see above); they also affect the digestion process. Connections with vegetative efferents allow gustatory sensations to influence the secretion of the digestive glands, and not only on its intensity, but also on the composition, depending, for example, on whether sweet or salty substances predominate in food.
With age
the ability to discriminate taste is reduced. The consumption of biologically active substances such as caffeine and heavy smoking lead to the same.
Viral genetic information in transformed cells
All cells transformed by the virus contain its genetic material. With the exception of the EB virus DNA, which is maintained in the lymphocytes transformed by it in the form of a plasmid, the viral DNA forged ...
Physicochemical foundations of the interaction of low-energy laser radiation with a biological object
The biomechanism of laser therapy is very complex and not fully understood. The impact on a living organism with low-energy laser radiation for therapeutic purposes refers to the methods of physical therapy. ...