Sense of taste: its components and operation
Eating is a pleasure. Most people enjoy a good dish, provoking pleasant sensations that in turn are spiced by the possible presence of company around (and that since ancient times, the time to feed has been something that has served as a social act, contributing to generate community). The fact that this act is pleasant at an organic level, apart from other considerations and elements, we owe it to a great extent to the sense of taste , which we are going to talk about throughout this article.
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The sense of taste and its usefulness
The sense of taste is one of our exteroceptive senses (next to sight, hearing, smell and touch), which allow us to capture the information from the environment. It is the ability to perceive and subsequently process the set of chemical properties of the elements we ingest, being especially linked to one of the basic life processes: food. Taste is what allows us to capture the flavors of food, something that allows us to choose and delimit the consumption of nutrients.
And it is not the consumed element itself that allows us to identify the flavor, but the processing that each of us does at a nervous level. In the same way, only this processing will mark if we perceive the taste as appetitive or aversive.
We are facing one of the most relevant senses when it comes to allowing our survival: the perception of taste it lets us know if a food is in good or bad condition , yes it could be toxic, or even understand if it contains some key elements that our body needs (sugar or salt mainly).
Another aspect to highlight about the sense of taste is that it is deeply linked to the other chemical sense we have: smell . Its connection is so close that, in fact, the sense of smell can affect the gustatory perception.
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The taste and its receptors
The sense of taste includes mainly the perception of five taste modalities, which have differentiated receptors to each other. Said modalities are the four already known: sweet, bitter, salty and acid, to which is added a recently discovered and little specified fifth, unami (which is associated with monoglutamate sodium present in some foods).
The receptors of the sense of taste are part of the taste buds of the tongue, palate and pharynx . Specifically, they are in the buttons or taste buds, these cells being bipolar and having a short life. In fact, the taste cells must regenerate continuously.
There are very different types of taste buds, each with a different amount and arrangement of the buttons that contain the receptors. Among them we found both basal cells, which would be still undifferentiated stem cells that will become receptors and that are generated every ten days to replace those that die, such as the receptor cells or chemoreceptors themselves.
These cells are not per se neurons but part of the epithelium , that will transmit the information to the fibers that supply them. There are also filiform papillae, distributed along the surface of the tongue but which are considered not to perceive the flavor but only contribute to the displacement of the food.
There is not a single kind of taste papilla, but we can find three mainly: the fungiforms which are distributed throughout the tongue and are especially located in the anterior tip, the foliate on the sides and the goblet spread in rows as long from the base of the tongue. The first would be the most numerous and the last the least (although the largest).
Flavors and receivers
Each of the flavors has a different set of receptors located especially in certain areas of the language , and that may be different in type and form from each other.
Bitter taste receptors are both ionotropic and metabotropic and are especially located in the innermost part of the tongue. The candy would be located especially at the tip of the tongue, possessing metabotropic receptors.
The salty would also be located at the tip and surroundings, their receptors forming a band on the surface of the tongue and these being of the ionotropic type. The acid, with also ionotropic receptors, would be found on the sides of the part of the tongue closest to the outside. The umami, on the other hand, is captured by the surface of the tongue.
The nerve pathways for taste perception
The sense of taste requires a large number of neural connections, given that in the recipient organ itself we can find very different types of receptors.
The information received by the taste recipients is first collected by the facial, glossopharyngeal and vagus nerves . Each of them supplies specific parts. The most anterior part of the tongue, where the fungiform cells are located, would correspond to the tympanic cord of the facial nerve. The posterior part is by the glossopharyngeal nerve. The vagus nerve would take over the receptors of the epiglottis and the palate.
These nerves would make a first relay in the nucleus of the solitary tract of the medulla, from which the information would travel to the protuberant taste area and after that to the ventral nucleus of the thalamus, the amygdala, the hypothalamus and the basal ganglia (which would add emotional components). to the perception of taste and would allow an approach or avoidance reaction). Finally, the data obtained would reach the primary gustatory cortex.
Alterations
The sense of taste has been essential for the human being throughout its evolution. But some people may have different alterations in the sense of taste that make it impossible or modify their perception.
The most extreme example of this is ageusia, or inability to capture any flavor. There is also hypogeusia or decreased ability to perceive . There are multiple disorders in this sense, but nevertheless what apparently is more usual is the existence of distortions in the perception of some of the flavors. And sometimes the problem is not in itself of taste, but rather it can occur at the olfactory level (which also gives us chemical information about food and is very linked to the perception of taste).
The causes of the sense of taste not working properly can be multiple. Among them we can find the presence of ear infections and respiratory system, the presence of dental problems, brain injuries that break or damage the nerve pathways that allow their perception or consumption of some drugs or substances. It also frequently appears as a result of the use of radio or chemotherapy in the treatment of cancer.
By last, some psychotic disorders or a manic episode they could alter the perception of taste due to the presence of gustatory hallucinations. Neurodegenerative diseases can also cause a loss of sense of taste and smell.
Bibliographic references:
- Gómez, M .; Espejo-Saavedra, J.M .; Taravillo, B. (2012). Psychobiology CEDE Manual of Preparation PIR, 12. CEDE: Madrid
- Guyton, C.A. & Hall, J.E. (2012) Treaty of Medical Physiology. 12th edition. McGraw Hill.
