Sense of taste: its components and how it works

Eating is a pleasure. Most people enjoy a good dish, eliciting pleasant sensations that in turn are spiced up by the possible presence of company around (and since ancient times, the moment of feeding has been something that has served as a social act, helping to generate community).

The fact that this act is pleasant on an organic level, regardless of other considerations and elements, we owe it largely 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 (together with sight, hearing, smell and touch), which allow us to capture information from the environment. It is about the ability to perceive and subsequently process the set of chemical properties of the elements that we ingest, being especially linked to one of the basic vital processes: the feeding. Taste is what allows us to capture the flavors of food, something that allows us to choose and limit the consumption of nutrients.

And it is not the element consumed itself that allows us to identify the flavor, but the processing that each of us does on a nervous level. In the same way, only this processing will mark whether we perceive the taste as appetizing or aversive.

We are facing one of the most relevant senses when it comes to allowing our survival: the perception of taste allows us to know if a food is in good or bad conditionYes, it could be toxic, or even understand if it contains some key elements that our body needs (mainly sugar or salt).

Another aspect to highlight about the sense of taste is that it is deeply linked to the other chemical sense that we have: smell. They are so closely linked that, in fact, the sense of smell can affect taste perception.

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Taste and its receptors

The sense of taste mainly includes the perception of five taste modalities, which have differentiated receptors. These modalities are the four already known: sweet, bitter, salty and acid, to which a fifth is added recently discovered and poorly specified, unami (which is associated with sodium monoglutamate present in some food).

Receptors of the sense of taste are part of the taste buds of the tongue, palate and pharynx. Specifically, they are found in the taste buds or buds, these cells being bipolar and having a short life. In fact, taste cells must continually regenerate.

There are very different types of taste buds, each with a different number and arrangement of the buttons that contain the receptors. Among them we find both basal cells, which would still be undifferentiated stem cells that will become receptors and that are generated every ten days to replace those that die, such as the receptor cells themselves or chemoreceptors.

These cells are not per se neurons but part of the epithelium, which will transmit the information to the fibers that innervate them. There are also filiform papillae, distributed along the surface of the tongue but which are considered not to perceive the taste but only contribute to the movement of the food.

There is not a single type of taste bud, but we can find mainly three: the fungiforms which are found throughout the tongue and They are especially localized on the anterior tip, the foliate on the sides, and the goblet scattered in rows along the base of the language. The former would be the most numerous and the latter the least (although the largest).

Flavors and receptors

Each of the different flavors has a series of receptors especially localized in certain areas of the tongue, and that they can be different in type and shape from each other.

Bitter taste receptors are both ionotropic and metabotropic and are especially located in the medial innermost part of the tongue. The sweet would be located especially on the tip of the tongue, possessing metabotropic receptors.

The salty one 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. Acid, with also ionotropic receptors, would be found on the sides of the part of the tongue closest to the outside. Umami, for its part, is captured by the surface of the tongue.

Nerve pathways for taste perception

The sense of taste requires a large number of neuronal connections, given that in the receptor organ itself we can find very different types of receptors.

Information received by taste receptors is first collected by the facial, glossopharyngeal and vagus nerves. Each of them innervates specific parts. The most anterior part of the tongue, where the fungiform cells are found, 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 in the epiglottis and the palate.

These nerves would make a first relay in the nucleus of the solitary tract of the medulla oblongata, from which the information would travel to the protuberant gustatory area and after that to the ventral nucleus of the thalamus, the amygdala, the hypothalamus and basal ganglia (which would add emotional components to the perception of taste and would allow a reaction of approach or avoidance). Finally, the data obtained would reach the primary taste cortex.

Alterations

The sense of taste has been essential for humans throughout their 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 the inability to capture any flavor. There is also hypogeusia or decreased ability to perceive. There are multiple disorders in this sense, but nevertheless what is apparently more common is the existence of distortions in the perception of some of the flavors. And sometimes the problem is not in itself of taste, but that can occur at the olfactory level (which also gives us chemical information about food and is closely linked to taste perception).

The causes that the sense of taste does not work properly can be multiple. Among them we can find the presence of ear and respiratory system infections, the presence of dental problems, brain injuries that break or injure the nerve pathways that allow its perception or the consumption of some medicines or substances. It is also common that it 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 taste hallucinations. Neurodegenerative diseases can also cause a loss of the sense of taste and smell.

Bibliographic references:

• Gómez, M.; Espejo-Saavedra, J.M.; Taravillo, B. (2012). Psychobiology. CEDE PIR Preparation Manual, 12. CEDE: Madrid
• Guyton, C.A. & Hall, J.E. (2012) Treaty of Medical Physiology. 12th edition. McGraw Hill.