Main types of taste sensitivity. Physiology of taste
1. Vestibular sensory system. Function of the vestibular system. Vestibular apparatus. Bone labyrinth. Membranous labyrinth. Otoliths.
2. Hair cells. Properties of receptor cells of the vestibular apparatus. Stereocilia. Kinocilium.
3. Otolithic apparatus. Otolith organ. Adequate stimuli for the receptors of the otolith organs.
4. Semicircular canals. Adequate stimuli for the receptors of the semicircular canals.
5. Central part of the vestibular system. Vestibular nuclei. Kinetoses.
6. Taste. Taste sensitivity. Taste sensory system. Taste reception. Taste time.
8. Central department of the taste system. Pathways of taste sensitivity. Kernels of taste.
9. Taste perception. Olfactory sensory system. Macromatics. Micromatics.
10. Smell(s). Classification of odors. Stereochemical theory of odors.
Microvilli membrane of taste cells contains specific areas (receptors) designed to bind chemical molecules dissolved in the liquid environment of the oral cavity. There are four types of taste sensations, or four taste modalities: sweet, sour, salty and bitter. Strict dependency between chemical nature of the substance and taste sensation no: for example, not only sugars have a sweet taste, but also some inorganic compounds (lead salts, beryllium salts), and the sweetest substance is saccharin, which is not absorbed by the body. Most taste cells are polymodal, meaning they can respond to stimuli from all four taste modalities.
Joining specific receptors molecules with a sweet taste activates the system of second 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 second messengers: 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) a specific G-protein gastducin, which regulates the intracellular concentration of cAMP, which controls the cation channels of the membrane and thereby determines the occurrence of the receptor potential. The action of salty taste molecules on receptors is accompanied by the opening of controlled sodium channels and depolarization of the taste cell. Substances with a sour taste close membrane channels for potassium ions, which leads to depolarization of the receptor cell.
The magnitude of the receptor potential depends on taste quality and chemical concentration acting on the cell. The emergence of a receptor potential leads to the release of a mediator by the taste cell, acting through a synapse on the afferent fiber of the primary sensory neuron, in which, 40-50 ms from the onset of the stimulus, the frequency of action potentials increases. Nerve impulses arising in the 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 reacting sensory fibers increases due to the involvement of high-threshold afferents in the transmission of information from the receptors.
Taste sensitivity
Taste 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 considered to be 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 it tastes salty. The maximum ability to distinguish between the concentrations of solutions of the same substance and, accordingly, the lowest differential threshold of taste sensitivity is characteristic of the average 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 thresholds of taste sensitivity vary individually, but the vast majority of people have the lowest threshold for identifying substances with a bitter taste. This feature of perception arose in evolution; it contributes to the refusal to eat substances with a bitter taste, which include alkaloids of many poisonous plants. Taste thresholds vary in one and the same person depending on his need for certain substances, they increase due to long-term use substances with characteristic taste(for example, sweets or salty foods) or smoking, drinking alcohol, 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 than other areas to sweets, 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 irritation with food thermoreceptors and mechanoreceptors of the oral cavity, as well as the effect of volatile food components on olfactory receptors.
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 to close range. At the same time, in fish, the sense of taste can also serve as orientation at long distances. In water, flavor substances move through 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, a person’s sense of taste performs an important function, triggering a number of reflexes. For example, washing the tongue with secretions from the serous glands is controlled by a reflex that is under the influence of the taste buds. The secretion of saliva is also triggered reflexively by corresponding stimulation of taste buds. Even the composition of saliva varies depending on the nature of the stimuli acting on the sensory cells, and taste stimuli also influence the secretion of gastric juice. Finally, it has been proven that vomiting is caused by the participation of taste sensitivity.
Literature
- 1. Batuev A.S., Kulikov G.L. Introduction to Physiology sensory systems. -- M.: graduate School, 1983. -263 p.
- 2. Lectures on central physiology nervous system: Tutorial. Faculty of Biology and Chemistry, Udmurt State University, Pronichev I.V. -- Powered by swift.engine.edu, 2003. - 162 p.
- 3. Shulgovsky V.V. Fundamentals of neurophysiology: A textbook for university students. - M.: Aspect Press, 2000. p. 277.
- 4. Shulgovsky V.V. Physiology of higher nervous activity with the basics of neurobiology: Textbook for students of biology. specialties of universities. - M.: Publishing Center "Academy", 2003. - 464 p.
Summary: there are four components in the perception of taste: the perception of sweet, sour, salty, bitter.
Taste sensitivity is the sensitivity of oral cavity receptors to chemical irritants. Subjectively, it manifests itself in the form of taste sensations (bitter, sour, sweet, salty and their complexes). When alternating a row chemical substances a taste contrast may occur (after salty water, fresh water seems sweet). A holistic taste image arises due to the interaction of taste, tactile, temperature, and olfactory receptors.
Sensitivity to different tastes varies. A person is most sensitive to bitter taste, which can be perceived in minimal concentrations. It is slightly less sensitive to sour, and even less to salty and sweet.
Absolute thresholds of taste sensitivity.
Methods for determining olfactory sensitivity. To determine taste sensitivity, use an eye pipette, with which drops are applied to the tongue: 1% sugar solution, 0.0001% quinine hydrochloride, 0.1% sodium chloride, 0.01% citric acid. After each test, rinse your mouth thoroughly.
The sensitivity of different parts of the tongue to taste stimuli is not the same. The most sensitive are: to sweet - the tip of the tongue, to sour - the edges, to bitter - the root, to salty - the tip and edges.
When perceiving complex tastes, the brain cannot differentiate the localization of taste: although there are few receptors in the middle part of the tongue, the taste is felt by the entire tongue.
Adaptation. After a sufficiently long-term effect of a taste stimulus on the taste buds, adaptation occurs in relation to it. It occurs faster in relation to sweet and salty substances, slower in relation to sour and bitter ones. So, if you act salty, then after 15 seconds the feeling of the intensity of this taste begins to disappear. The adaptation time depends on the degree of concentration of the stimulus solution. The higher the concentration, the faster adaptation occurs. To restore taste sensitivity, just rinse your mouth clean water, after which sensitivity will be completely restored.
The contrast effect is detected in the taste analyzer. Once acclimated to sweets, salty flavors will seem saltier. Moreover, after adaptation to sucrose, fructose and saccharin pure water seems sour and bitter, and conversely, adaptation to bitter substances such as quinine or black coffee causes water to taste sweet. If you adapt to salty taste, then the same pure water will seem sour or bitter, and after adaptation to salts, it will seem sour, sweet and slightly bitter, and adaptation to sour, for example, to a solution of citric acid, will seem sweet. The most difficult thing to achieve as a result of this aftereffect is a salty sensation. This may be due to the fact that saliva already contains salt.
With age, the number of taste buds decreases, and along with this, sensitivity to taste decreases. Drinking alcohol and smoking accelerate the loss of taste.
Regarding the sense of taste, there is evidence of synesthesia: taste, along with smell, affects the sensitivity thresholds of other modalities. For example, visual and hearing acuity may increase, as well as changes in skin and proprioceptive sensitivity.
Taste qualities.
Humans distinguish four basic taste qualities: sweet, sour, bitter and salty.
which are quite well characterized by their typical substances. 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
are characteristic of many natural taste 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 identified.
Bitter taste is perceived mainly by the base of the tongue; other taste qualities affect its side surfaces and tip, and these zones overlap.
Between chemical properties
substance and its taste
there is no one-to-one correlation. For example, not only sugar, but also lead salts are sweet, and the sweetest taste is found in artificial sugar substitutes such as saccharin. Moreover, the perceived quality of a substance depends on its concentration. Table salt tastes sweet in low concentrations and only becomes purely salty when the concentration 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 cause vomiting or the urge to vomit. Emotional Components
taste sensations vary widely depending on the state of the body. For example, a person experiencing a salt deficiency considers the taste acceptable, even if its concentration in food is so high that a normal person would refuse the food.
The sense of taste is apparently very similar in all mammals. Behavioral experiments have shown that various animals distinguish the same taste qualities as humans. However, recording the activity of individual nerve fibers also revealed some abilities that humans lack. For example, "water fibers" have been found in cats, either responding only to water stimulation or exhibiting a taste profile that includes water among the effective stimuli.
Biological significance.
The biological role of taste is not only to test 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.
Why is the same dish perceived differently by different people? For example, soup seems wonderful to you in its original form, but your significant other wants to add pepper or salt to it. In the first case we're talking about about the category of people “supertasters”, on whose tongue there are many papillae and the taste seems full. As a rule, “supertasteers” prefer soft food instead of spicy food, and they like to add cream to their coffee. The category of people with low papillary density - “subtasters” - love spicy foods that “burn” the oral cavity. Although taste sensitivity is influenced not only by the papillae.
It is known that the human brain distinguishes five tastes - sour, salty, bitter, sweet and umami (the rich exotic taste of oriental food). However, the set of chemicals that cause these signals differs among different people. Experts note that humans have between 20 and 40 genes responsible for bitter taste detectors.
Different perceptions of bitterness are most likely a consequence of evolutionary pressure in different parts of the planet. The most poisonous plants endowed with a bitter taste and nomadic tribes that came into contact with different types of plants over time received different receptors.
Residents of countries where malaria is common are likely to have a gene that makes them less sensitive to certain bitters, especially those containing cyanide. Researchers believe that cyanide in small quantities can neutralize malarial insects without poisoning humans. By the way, people have a natural aversion to bitterness and certain odors, which is why the beer beloved by many is rarely liked by anyone at the first try.
If you want to understand whether you are a “super tester” or a “sub tester,” put food with blue dye on your tongue. This blue paint unable to adhere to taste buds on the tongue. If there is little blue left on the tongue, you are a “supertester”; if the entire tongue turns blue, you are a “subtester”.