Sense of taste: its components and functioning

It is one of the most important senses, and is related to smell.

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

The fact that this act is pleasurable 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.

The sense of taste and its usefulness

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 ability 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 delimit the consumption of nutrients.

And it is not the consumed element itself that allows us to identify the taste, but the processing that each of us does at the nervous level. In the same way, this processing alone will determine whether we perceive the taste as appetitive or aversive.

We are dealing with one of the most relevant senses in enabling our survival: the perception of taste allows us to know whether a food is in the right state or not. allows us to know whether a food is in good or bad condition.If it does, it could be toxic, or even understand if it contains some key elements that our organism 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: the sense of smell. is that it is deeply linked to the other chemical sense at our disposal: the sense of 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 modalities, which have receptors that are differentiated from each other. These modalities are the four already known: sweet, bitter, salty and sour, to which is added a fifth recently discovered and little specified, the unami (which is associated with sodium monoglutamate present in some foods).

Taste receptors are part of the taste buds of the tongue, palate and pharynx. are part of the taste buds of the tongue, palate and pharynx.. Specifically, they are located in the taste buds, which are bipolar cells and have a short life span. In fact, taste cells must be continuously regenerated.

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

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

There is not a single type of taste bud, but we can find mainly three: the fungiform ones which are distributed along the whole tongue and are especially located at the anterior tip, the foliated ones on the sides and the goblet papillae scattered in rows along the base of the tongue. The former would be the most numerous and the latter the least (although the largest).

Tastes and receptors

Each of the tastes has a different set of receptors located especially in certain areas of the tongue. located especially in certain areas of the tongueThey can be different in type and shape from each other.

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

The salty one would also be located in the tip of the tongue and its and surroundings, its receptors forming a band on the surface of the tongue and being of ionotropic type. Acid, with ionotropic receptors, would be located on the sides of the part of the tongue closest to the exterior. Umami, on the other hand, 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.

The information received by the taste receptors is first of all picked up 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 located, corresponds to the tympanic cord of the facial nerve. The posterior part is supplied by the glossopharyngeal nerve. The vagus nerve would take over the receptors of the epiglottis and 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 protuberancial gustatory area and then 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 allow an approach or avoidance reaction). Finally, the data obtained would reach the primary gustatory cortex.

Alterations

The sense of taste has been primordial for human beings throughout their evolution. But some people may have different alterations in the sense of taste that make it impossible or modify its perception.

The most extreme example of this is ageusia, or the impossibility to perceive any taste. There is also hypogeusia, or reduced ability to perceive taste.. There are multiple disorders in this sense, but what is apparently more usual is the existence of distortions in the perception of some of the flavors. And sometimes the problem is not in itself of the taste, but it can occur at the olfactory level. can occur at the olfactory level (which also gives us chemical information about food and is closely 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 and Respiratory system infections, the presence of dental problems, brain injuries that break or damage the nerve pathways that allow its perception or the consumption of some drugs or substances. It is also frequent that it appears 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 taste perception due to may alter the perception of taste due to the presence of gustatory 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.