Eating is a pleasure. Most people enjoy a good dish, giving rise to pleasant sensations which in turn are spiced up by the possible presence of company around them (since ancient times, the moment of eating has been something that has served as a social act, contributing to the creation of community). The fact that this act is pleasant at an organic level, apart from other considerations and elements, is largely due to the sense of taste , which we will talk about throughout this article.

The sense of taste and its utility

The sense of taste is one of our exteroceptive senses (along with sight, hearing, smell and touch), which allow us to capture information from the environment. It is the capacity to perceive and subsequently process the set of chemical properties of the elements we ingest, being especially linked to one of the basic vital processes: food. Taste is what allows us to capture the flavors of food, something that allows us to choose and delineate the consumption of nutrients.

It is not the element itself that is consumed that allows us to identify the taste, but the processing that each of us does on a nervous level. In the same way, only this processing will mark if 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 condition , if 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 we have: smell . Its link is so close that, in fact, the sense of smell can affect taste perception.

Taste and its receptors

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

The taste receptors are part of the taste buds on the tongue, palate and pharynx . Specifically, they are found in the taste buds, these cells being bipolar and having a short life span. In fact, taste cells must be continuously regenerated.

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

These cells are not neurons per se but part of the epithelium , which will transmit the information to the fibres 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 only one type of taste bud, but we can find mainly three: the fungiforms which are spread all over the tongue and are especially located at the anterior tip, the foliated ones at the sides and the goblet ones spread in rows along the base of the tongue. The first ones would be the most numerous and the last ones the least (although the biggest ones).

Flavors and receivers

Each of the flavors has a different set of receptors located especially in certain areas of the language , and which may be different in type and form from each other.

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

The salt would also be located at the tip and around it, its receptors forming a band on the surface of the tongue and being ionotropic. The acid, with receptors also ionotopic, would be found on the sides of the part of the tongue closest to the exterior. The umami, on the other hand, is picked up by the surface of the tongue.

The nerve pathways for taste perception

The sense of taste requires a large number of neural connections, since in the receiving organ itself we can find very different types of receptors.

The information received by the taste receptors is first collected by the facial, glossopharyngeal and vagus nerves . Each of them has 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 the glossopharyngeal nerve. The vagus nerve would take care of the epiglottis receptors and the palate.

These nerves would make a first relay in the nucleus of the solitary tract of the spinal bulb, from which information would travel to the pro-tuberant-like area and then to the ventral nucleus of the thalamus, the amygdala, the hypothalamus and the basal ganglia (which would add emotional components to taste perception and allow an approach or avoidance reaction). Finally, the data obtained would reach the primary gustatory cortex.

Alterations

The sense of taste has been fundamental for the human being throughout his evolution. But some people can 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 is apparently more common is the existence of distortions in the perception of some of the flavours. And sometimes the problem is not the taste itself, but rather can occur at the olfactory level (which also gives us chemical information about the food and which is closely linked to the perception of taste).

There are many reasons why the sense of taste does not work properly. Among them we can find the presence of ear and respiratory system infections, the presence of dental problems, brain injuries that break or damage the nerve pathways that allow their perception or the consumption of some drugs or substances. It is also frequent to appear as a result of the use of radio or chemotherapy in the treatment of cancer.

Finally, some psychotic disorders or a manic episode may 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. Manual CEDE de Preparación PIR, 12. CEDE: Madrid
  • Guyton, C.A. & Hall, J.E. (2012) Treatise on Medical Physiology. 12th edition. McGraw Hill.