Taste
As gustatory perception of the subjectively experienced experience of sensations of taste is referred to, which are caused by stimulation of specific sensory organs of taste (Latin: Augustus ) as the taste buds.
The sense of taste is like the smell addressed by chemical stimuli, however, is a Nahsinn, can be checked before the actual income with the ingested food. In adult humans, the sensory cells of the taste organ located in the tongue and throat and give five ( or six) basic qualities. Sour and bitter taste may indicate immature, fermented or poisonous food. The taste qualities of sweet, salty, umami ( and fat ) characterize a food roughly according to their content of nutritionally important substances.
The sensation, which is usually referred to as " taste " is an interplay of taste and smell together with tactile and temperature sensations from the oral cavity. Sense Physiologically, however, includes the human sense of taste only the mentioned basic taste qualities; they will be perceived by taste receptors located predominantly on the tongue.
As dysgeusia disturbances of taste perception are called. Ageusia is, the loss of taste.
- 3.1 Sweet, bitter and umami
- 3.2 Salty and sour
- 3.3 calcium / magnesium ions
Location of the sensory cells
The receptor cells for different taste qualities are arranged in mammals taste buds ( Caliculi gustatorii ), the ( gustatoriae papillae ) on the tongue in the papillae of the tongue, adjacent to it in the mucous membranes of the oral cavity, pharynx and throat. About 25% of the taste buds are located on the anterior two-thirds of the tongue, a further 50 % to the rear third. The remainder work on soft palate, nose, pharynx, larynx and upper esophagus. Each taste bud can contain 50 to 150 sensory cells, also depends on the species of a mammal, and a Geschmackspapille then some to numerous taste buds.
The papillae of the tongue are divided according to their form in Wall, leaves, mushroom and Fadenpapillen. Papillae ( vallate papillae ) are located in the posterior third of the tongue dorsum in a V- shaped arrangement near the base of the tongue. Every person has about seven to twelve of these papillae, each of which has several thousand taste buds. The Blätterpapillen ( foliate papillae ) are located in the posterior third of the tongue, but at its edge, and contain several hundred taste buds. The up to four hundred Pilzpapillen ( fungiform papillae ) are found over the entire surface of the tongue is distributed mainly on the anterior two thirds of the tongue and contain in humans three to five taste buds. Fadenpapillen ( filiform papillae ) do not contain taste buds but are used to assess mechanical properties of the recorded food.
Human infants and young children have not only numerically more taste buds, but also that on the hard palate, in the middle of the tongue and the lips and buccal mucosa. With increasing age they are concentrating their numbers thinned by and to certain locations.
The taste qualities
: Basic qualities of taste assumed - News is at least five - six may
Umami (Japanese for ' savory, spicy ') is a commonly less well-known taste quality, which was first described in 1908 by the Japanese researchers Kikunae Ikeda. He found this in the investigation of a ( traditionally made from seafood) seasoning sauce after its flavor components, and gave her name as this quality composite of umai ( ' spicy ') and mi ( ' taste '). A strong umami taste indicates protein and amino acid- rich foods, but can also be caused solely by a high concentration of glutamic acid or by the flavor enhancer monosodium glutamate.
Crystal structure of sodium chloride - table salt
Citric acid
Quinine - Bittern of China Beef trees
L-glutamic acid
Since the beginning of the 20th century is known that the mentioned qualities of taste are probably trigger different degrees in different regions on the tongue, but in principle of all the sensitive areas. Although the differences between the tongue areas with respect to the sensitivity for individual qualities in humans are rather small, yet to find " taste zones " in many textbooks, a division of the tongue.
More taste qualities
A group of scientists led by Philippe Besnard in late 2005 identified a potential taste receptor for fat: the glycoprotein CD36, which was detected in the taste receptor cells of the tongue and can bind fatty acids with high affinity. Until then, it was debatable whether there is a sixth basic quality that is caused by fat in foods. It was generally assumed that the preference for fatty foods derived solely from their smell and consistency. To clarify the question of a possible further basic taste for fat, the researchers conducted experiments with normal (wild type) and with genetically modified mice lacking the CD36 receptor by ( knockout mice). The mice were choosing between two food offerings left, one of which contained fat and the other simply a substance that imitated the consistency of the fat. It was found that the normal mice with CD36 had a strong preference for the fatty food, but not the knockout mice lacking CD36. In addition, only the ordinary mice responded to fatty food with the production of fat- specific digestive juices. From these results one can conclude an involvement of CD36 in the perception of fat in the diet of rodents.
Meanwhile, it was also demonstrated by researchers from the same group that stimulation of taste receptor cells of the mouse that express CD36, with linoleic acid leads to activation of intracellular signaling cascades and the release of neurotransmitters.
Linoleic acid is a component of many vegetable fats found in food and in the oral cavity by specific enzymes (lipases ) are released. The release of neurotransmitters by taste receptor cells is necessary for forwarding the information to the brain where they are processed.
The existence of such a further taste quality was supported in 2010 by a smaller study with 30 subjects. The subjects were able to differentiate various fatty acids in otherwise tasteless solutions. Furthermore, a relationship between BMI and the sensitivity of taste quality was shown. Accordingly consumed subjects with a more sensitive sense of taste for fatty acids less fat than those with a less sensitive.
2011 took a Berlin research group led by Galindo is a connection between the sensation of taste greasy, scratchy in the presence of long-chain fatty acids in taste samples and the already known of mice receptor GPR120. They showed in an expression analysis that GPR120 genes are expressed in human taste receptor cells.
In addition, other taste qualities are repeatedly discussed how alkaline, metallic and water -like.
An essential role for complex taste sensations does the sense of smell, which is for all the other " taste sensations " responsible. This is evident in severe colds, if you do not taste impressions beyond the basic categories perceives more with nasal congestion. Also, there are many species no separation between taste and smell perception.
" Sharp " is indeed qualified as taste sensation, but is actually a pain signal to the nerves in foods that are spiced with chili, for example, then caused by the alkaloid capsaicin.
Taste receptors
The taste qualities bitter, sweet and umami are mediated by G protein- coupled receptors and signal transduction is now quite well characterized. The details of the perception of sour and salty, however, are still largely unknown. Due to the chemical structure of the salty and sour tasting substances seems likely that ion channels play a crucial role in the perception.
Sweet, bitter and umami
For the perception of the sweet taste of a heterodimeric receptor is responsible, which is composed of the two G- protein -coupled receptors T1R2 and T1R3. This heterodimer mediates the sweet taste of all for the people of sweet-tasting substances, although they have very different molecular structures. The ability to detect a wide variety of materials is accomplished by the extremely long extracellular N-terminus of the receptor subunits. Of binding of the different substances different parts of the N -terminus are required. All species of the cat family have a mutation in the T1R2 gene, which is why they have no Süßwahrnehmung.
The receptor for umami taste is very similar in structure. He, too, is a heterodimer, but he shall be composed of one each T1R1 - T1R3 and subunit. It is able to recognize different L-amino acids, and shows a high specificity for the human amino acids glutamic acid and aspartic acid. The presence of purine nucleotides, such as inosine and guanosine, leads to an enhancement of receptor activation and thus also of the umami taste.
In contrast to the different taste qualities is responsible for the perception of bitter taste of a variety of receptors. They form the gene family of T2RS, which has about 25-30 members in humans. The individual T2R - types - expressed in the same receptor cells - in various combinations. The result is that, although the individual receptors are sometimes very specific for one or a few bitters, Mammals various bitter substances can not distinguish the taste. Through all the bitterness, the same receptor cells are activated and ultimately forwarded the same information to the brain. Some bitter substances are also able to influence signal transduction directly, by inhibiting or activating enzymes involved. Receptors for bitter substances were also found on smooth muscle cells of the bronchial system. There, their activation causes bronchodilation.
Although the receptors are different for sweet, umami and bitter, as is the intracellular signaling cascade that they abut the same: At the G- protein-coupled receptors, the heterotrimeric G- protein gustducin is bound to the structurally closely related to the transducin from the rods of the retina is. The α - subunit of the Gustducins has idle bound a Guanosindiphosphatmolekül (GDP ). The binding of the flavor substances to the G- protein-coupled receptors leads to the replacement of GDP by guanosine triphosphate (GTP) and the dissociation of gustducin in the α subunit, and a βγ dimer. In the following results in activation of phospholipase Cβ2 ( PLCβ2 ) which befindliches in the membrane phosphatidylinositol -4 ,5- bisphosphate ( PIP2 ) into the two second messenger inositol triphosphate (IP3 ) and diacylglycerol (DAG) split. IP3 leads by opening gated calcium channels, IP3 of the endoplasmic reticulum to the increase in the intracellular Ca2 concentration. This has the opening of TRPM5 channels and the depolarization of the taste sense cell.
Salty and sour
For a long time the epithelial sodium channel was considered as the main candidate for the receptor of the salt taste in humans. Today we know that he is indeed heavily involved in rodents at the salty taste perception, but plays only a minor role in humans. It is believed that in addition to cations such as Na , and the anions of the salts, such as Cl -, have an impact.
Contrary to longstanding assumptions seem to play a crucial role in the detection of the less acidic taste of the extracellular, rather than intracellular pH in the taste receptor cells. This would also explain why at the same pH value of a solution organic acids such as acetic acid or citric acid taste significantly as inorganic acids such as hydrochloric acid. The organic acids are substantially non-polar as the inorganic and thus better able to overcome the cell membrane in undissociated state. The cells then dissociate into protons and anionic acid residues and therefore lower the intracellular pH. The inorganic acids, however, can not penetrate the cell membrane undissociated. Only at sufficiently high concentrations being incurred by extracellular protons dissociation ( or its hydrated forms ) on ion channels in the receptor cells. So only carry significantly higher concentration of inorganic acids in the oral cavity at the same lowering of the pH in the sensory cells. It is believed that the low pH changes in the intracellular levels of membrane proteins and, finally, leads to the activation of the above cell receptor.
As the search proceeds according to the actual receptor for the taste quality "sour" sluggish. After the last few decades a number of theories various ion channels and transporters were proposed as sour receptor, in 2006 with the transmembrane protein PKD2L1 a particularly interesting candidate was (short for engl. " Polycystic kidney disease 2 -like 1 " ) identified. It has been shown that longer held by oxygen stimuli in mice in which the selectively PKD2L1 -expressing cells have been killed, no activation of the corresponding nerves. The other taste qualities were apparently not affected.
Through a series of experiments, we now know that each taste receptor cell only contains receptors for a particular taste quality, ie the detection takes place separately at the level of the sensory cells. However, a taste bud contains the sensory cells of several qualities. And also in the associated afferent nerve fiber color codes each for more than one taste quality.
Calcium / magnesium ions
The results of investigations of the Monell Chemical Senses Center by Tordoff suggest that there could be a taste for quality calcium / magnesium ions. Receptors were found during the studies on the tongue of mice react specifically calcium / magnesium ions.
Since a strain of mice in the comparison test calcium-containing liquid ( probably because of the taste ) preferred, whose genome has been examined more closely. Two genes were identified that are apparently involved in the formation of calcium / magnesium - specific taste receptors. One of the genes is also involved in sweet and umami receptor. These two receptors are also constructed as heterodimers by combination of two different gene products ( see above). In addition to the gene TAS1R3 is still CaSR be necessary for the calcium / magnesium taste in mice. The responsible genes are also present in the human genome, but were products of the second-mentioned gene in humans so far only structures in the brain and associated with the digestive system.
Neural processing
The transfer of information from the (secondary) taste receptor cells on the afferent neurons that are responsible for forwarding to the brain is still unclear. It is known that taste cells were able to distribute a number of neurotransmitters and neuropeptides, such as serotonin, norepinephrine, γ -aminobutyric acid, cholecystokinin and neuropeptide Y. There are further evidence that adenosine plays an important role in the signal transmission from the sensory cell to nerve cell.
The taste information is sent to the brain vagus (X) in mammals over the three cranial nerve facial nerve (VII ), glossopharyngeal (IX) and vagus. There, the first interconnection in the rostral portion of the nucleus of the solitary tract takes place. From there, the taste information reaches further into the ventral posteromedial nucleus pars parvocellularis ( VPMpc ) of the thalamus. In primates this is done by a direct projection, in rodents, however, are available with the nucleus parabrachial a stopover on the way to the thalamus. The VPMpc the thalamus projected his part in the island cortex, in which the primary gustatory cortex is located. This already takes place integration with other sensory impressions, mainly tactile and temperature information from the oral cavity. The secondary gustatory cortex, the next higher station of taste processing, is located in the orbitofrontal cortex and partially overlaps with the secondary olfactory cortex. In addition to the described here " main route " there are multiple branches at each level of processing. This result, among others, to the hypothalamus and the limbic system. There are also numerous interconnections of higher returns at lower levels.
Sensory processing
The complexity of gustatory perception is achieved by a combinatorial system of representations in the brain, which allows a detailed analysis of the intricacies of a sensory impression. This system of our nervous system, the vector encoding, can be understood as a representation in a feature space (with six basic tastes a six-dimensional space ). A certain taste is represented in this room by an activation pattern of all six types of receptors. Could the tongue per basic tastes differ only ten levels of intensity, so deceiving the total number of distinct activation patterns but 106 = 1,000,000. With only six different types of receptors could therefore differentiate a million different flavors. From simple basics thus grows combinatorially a variety of discriminating and perceptive possibilities.
" Taste ", " smell" as a word in the sense of
The German dictionary of the Brothers Grimm is the meaning of the word taste even double in Old High German and Middle High German relationship to " B.bedeutung.das verb refers in older language sowol the smell than the taste sensations. developed NHG written language, the first of the two to use have given up, on the other hand it is preserved in the Upper German dialects, for even in part under ausschlieszung the second. "
Thus, at least in the language area of the Alemannic (Baden- Württemberg, Switzerland ) and Bavarian ( Bavaria, Austria ) " taste " dialects of German, the term occasionally lead to confusion, say the speakers of these dialects " taste " with but a conceptual field that also or only the meaning ' smell ' includes ( " through the nose taste " ), in contrast to the NHG. One older example of a resulting misunderstanding can be found at the beginning of the second part of the novel The Günderode of Bettina von Arnim (1840 ), where it is told of a gentleman Arenswald who had eaten a number stinking worm that had touted him as a worm, " the very taste ".
As for the noun form and flavor of the designated with this word semantic field exist - outside the specialist language use - similar conditions that make possible misunderstandings. At the designated also as "taste" complex sensation in food intake usually carries the smell of a food at much.