taste and smell

Relationship between the taste and smell in the human body

Taste and smell are two senses that, although important, have always been overshadowed by others such as sight or hearing. This implies that little has been studied. However, we do know that there is a relationship between taste and smell.

In this article, we will know this link between the two senses. Did a dish ever smell so good that you thought, “If it tastes as it smells it’ll be delicious!” Here we will find out if there really is as much relationship between these two senses, as had always been thought.

How do these senses work?

Until a smell is perceived, a series of steps are taken: first, the odorants enter the nasal cavity and are detected by the metabotropic receptors. Transduction occurs, that is, the process by which a cell converts a certain signal or external stimulus, into another specific signal or response. Then a system of second messengers is activated that causes the depolarization of the sensory neuron and the action potential.

The smell is also the only sensory system whose information does not relay into the thalamus before reaching the primary cortex. Also, cortical processing is ipsilateral; this means that the information does not change sideways in the brain, i.e. the information entering through the left hole of the nose is processed in the left hemisphere and the same with the right side.

Olfactory cells are bipolar; sensitive axons have synapsed with the olfactory bulb’s dendrites in units called glomerules.

The olfactory system is divided into two:

  • Main system
  • Accessory or vomeronasal system

As for the ability to perceive flavours, there are 4 submodalities of taste (taste types): salty, sweet, acidic and bitter (although recently a new one, umami) has been discovered. At the brain level, the receptors for acid and salt are ionotropic, and the receptors for sweet taste are metabotropic; both types of receptors act for bitterness.

Here the sequence given at the brain level to end up appreciating the flavours is as follows: the taste information is transported by the facial cranial nerves (VII), Glosopharynx (IX) and Vague (X).

Unlike olfactory information, taste information makes a relay in the brain; the first relay is in the Lone Track Core (bulb). Then that information goes to the protuberance taste area, and from there to the Posteromedial Ventral Core of the Tálamo (mostly ipsilateral pathways). Eventually, the neurons project to the Primary Gustative Cortex.

The relationship between taste and smell

But what is the relationship between taste and smell? Let’s get to know her in detail.

A group of scientists from the Institute of Neurosciences of Castilla y León (INCYL) of the University of Salamanca are developing various studies on the relationship between taste and smell. One of his researchers, Eduardo Weruaga, claims that many times people confuse concepts such as taste, taste and smell, but that they are very different things.

When we taste something, in reality, the olfactory component is much more important than the taste component, although we usually think otherwise. That’s why when we have colds we stop noticing the flavours (“everything tastes like nothing”), because of our nasal congestion (our smell is “cancelled”).

In line with these claims, it is also known that many people who begin to lose the taste of food and who believe that they are losing their taste, what they are actually losing is the smell, the main component of that feeling.

Results to studies

To explain the relationship between taste and smell, the group of scientists from the Institute of Neurosciences of Castilla y León (INCYL) of the University of Salamanca, together with the Spanish Olfactory Network, held five years ago a series of workshops where they presented these two senses, and experimented with substances that stimulated them.

This group states that not everyone smells and likes the same and that some have greater potential than others. They also argue that there is a genetic component that would explain why there are some “super-tasting” people and others who are precisely the opposite. As for the smell, this is more unknown.

Differences and similarities between taste and smell

Continuing the relationship between taste and smell, we know that the only neurological relationship between these senses is that both are “chemical senses”, as they identify chemicals of the environment.

Eduardo Weruaga, the researcher, notes that “smell detects volatile chemicals that are dissolved in the air, which cannot be done by taste buds in the mouth, and taste detects substances dissolved in water.” These are two means of the environment that do not mix in nature, making us detect the different substances by different pathways.

On the other hand, the relationship between taste and smell is present for example in different foods, or in the fact that we perceive that “taste and smell” are united (although at the brain level they are not really). To illustrate the latter, consider, for example, when we say “this dish tastes like how it smells”, or “if it tastes as it smells, it will be great”.

In short, according to these studies, the neural pathways of taste and smell have nothing to do with each other, although the perception of these occurs together once it reaches the brain.

Pathologies with loss of smell

Humans place greater importance on vision or hearing than taste and smell (unlike other animals). This makes the taste and smells so little studied, even if there are about 300 pathologies that include among their symptoms the loss of smell. Total loss of smell is called anosmia, and partial loss, hyposmia.

For example, Parkinson’s or Alzheimer’s comes with certain neurological losses that affect smell. However, experts say that smell is often lost from causes beyond neurology, such as plugging the nostrils by polyps (additional tissue parts that grow inside the body).

In colds or colds, we can also lose our sense of smell; even, albeit on fewer occasions, permanently.

The emotional memory associated with odours

On the other hand, smell, unlike other senses (including taste), is a type of perception or very emotional sense, since it is connected with brain areas responsible for managing emotions.

Olfactory memory is said to be the most powerful. Those olfactory memories (certain smells or scenes associated with a particular smell) are also remembered much more if they are also emotionally charged.

References:

  • Ibero-American agency for the dissemination of science and technology. (2014).
  • Carlson, N.R. (2005). Behavioural physiology. Madrid: Pearson Education.
  • Netter, F. (1989). Nervous system. Anatomy and physiology. Barcelona: Salvat.

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