Rhinencephalon: what is it, its parts and functions in the brain?

This part of the brain is involved in the processing of smells and emotions.

The functioning of the human brain is based on four main blocks: the neocortex, in charge of motor activity, planning and attention; the basal ganglia, responsible for movement control; the reticular formation, in charge of vital functions such as sleep, wakefulness and Cardiovascular control; and the limbic system, formerly known as the rhinencephalonthe center of emotional management and the olfactory system.

Let's see what exactly is the rhinencephalon, and what brain functions are attributed to it.

What is the rhinencephalon?

The rhinencephalon is currently referred to as the part of the brain related to smell and included within the limbic system or "emotional brain"..

With the increase in the differentiation of the other senses in vertebrates, olfaction has been losing prominence. However, the fundamental connections of the olfactory mechanism with both visceral and somatic activities are as important in humans as in other mammals, although olfactory sensitivity is lower.

The rhinencephalon, being interconnected with the hypothalamus (center in charge of homeostasis or organic balance) and with several areas of emotional control, helps us to concentrate all the information that comes from the outside and that we translate into processes and that we translate into processes through which we perceive, learn, act and remember.

We must not forget that the sense of smell is up to 10 thousand times more sensitive than any other of our senses, and that the olfactory response is immediate and extends directly to the brain. It is also estimated that we have 100 million receptors for olfactory sensation.

It is believed that **human beings can capture up to 7 primary odors up to 7 primary odors: camphor, musk, flowers, mint, ether, pungent and rotten, which correspond to the seven types of receptors in the olfactory mucosa.These odors correspond to the seven types of receptors in the olfactory mucosa. However, research data from recent years indicate that there are at least a hundred primary odor sensations.

Localization in the brain

In humans, we can localize the rhinencephalon in the lateral lower part of the brain, just between the eyes, and above it is the frontal lobe..

In the upper portion of the nasal cavity there is a small area called the olfactory epithelium. This area contains between 10 and 100 million olfactory receptors, each of which is actually a neuron that possesses olfactory cilia sensitive to the chemical stimuli of odorant substances.

These neurons emit prolongations that gather in groups (called axons) and form two nerves known as olfactory nerves. These are directed towards the brain and end their journey in an area of gray matter called the olfactory bulb. The information will travel a path from the bulb, through the olfactory tract, to the primary olfactory area of the cerebral cortex..

It is in the cortex where we finally perceive a particular odor consciously, and from this cerebral area depart the nerve pathways that communicate with other systems such as the limbic or hypothalamus, areas responsible for many of the emotional responses associated with odors or olfactory memories.

Parts of this structure of the nervous system

The bodies of these neurons emit prolongations called axons that gather in groups and are grouped to form two nerves called olfactory nerves. These approach the brain and end in an accumulation of gray substance called olfactory bulb.

The captured information passes through the bulb and reaches other structures of the limbic system, a network of interconnected structures located near the medial part of the brain. The main structures of this system, of which the rhinencephalon is a part, are as follows:

1. Hypothalamus

This brain structure, located in the diencephalon, plays a fundamental role in the regulation of vital functions such as body temperature, hunger and thirst, sexual impulses and mood regulation.

It does all this by acting as a bridge between the cerberus and the diencephalon. as a bridge between the cerberus and the endocrine system.The liver, discharging torrents of hormones and playing a coordinating role of the autonomic nervous system.

2. Hippocampus

It is a small curved and elongated structure, located in the inner part of the temporal lobe, very close to the thalamus and the amygdalae. It is involved in the regulation of mental processes such as memory, memory retrieval, spatial localization or orientation..

Although at first it was thought that this structure was directly involved in olfaction as a central component of the hindbrain, today its involvement in odor memory is more debated.

3. Amygdala

The amygdalae are located next to the hippocampus and, therefore, we have one in each cerebral hemisphere. Their function is related to the learned emotional response elicited by certain contexts and elicited by certain contexts and situations, and therefore also with emotional learning.

This structure is therefore one of the main control nuclei of emotions such as fear or anger. This is why it is important structure to understand how odors can alter our mood, arouse emotions or evoke memories.It is therefore an important structure for understanding how odors can alter our mood, arouse emotions or evoke memories.

4. Orbitofrontal cortex

At the limits of the limbic system we can find the orbitofrontal cortex, the escape valve for emotional commands to areas of the frontal lobe responsible for the generation of strategies and frontal lobe in charge of strategy generation and planning.

Therefore, it has a very important role in placating the most primitive and "irrational" impulses coming directly from the limbic system and acting as a filter for some signals, letting only those that serve to achieve the objectives defined in the medium or long term goals.

5. Olfactory bulb

It is a small vesicular structure composed of a pair of protrusions located in the olfactory epithelium and below the frontal lobes.. It is believed to be responsible for detecting, differentiating and amplifying odors and our sensitivity to them. This structure also stands out for being an area where there is adult neurogenesis, that is, generation of new neurons throughout life.

In animals, it influences sexual behavior, defensive and aggressive behaviors, as well as the care of offspring.

Functions

Our hindbrain converts chemical signals into perception and electrical impulses that travel through our brain in order to fulfill in order to fulfill the following vital functions:

• Survival: detection of harmful substances, pollutant gases and decaying food.
• Collaboration with the sense of taste in the perception of food flavors.
• Identification of a wide variety of odors (between 5,000 and 10,000).
• Reinforcement of memory by association of odors and memories.
• Distinction of new smells among environmental smells in the background.
• Detection of environmental information.
• Creation of an odor representation.
• Detection of a mating partner (has been lost in humans).
• Detection and orientation to a nutrient source (mainly in non-human animals).
• Assessment of nutrient status, type and quality (in non-human animals).

The olfactory system and memory

Another body structure to take into account when talking about the olfactory system, beyond the importance of the rhinencephalon, is one known to all of us: the nose, the olfactory organ par excellence. If it were not for it, we would be unable to perceive the vast range of odors that our towns and cities emanate day and night. However, the processing of odors goes beyond the nose, the processing of odors goes beyond this highly visible part of our body..

Olfactory molecules that are dispersed in the environment come into contact with the nasal mucosa and reach the receptors of the olfactory epithelium. The receptor neurons send the information to the olfactory bulb by means of electrical impulses. And from there, to the limbic system, in charge of centrifuging our brain, stimulating our memory system and associated emotions..

When we perceive a specific smell, we look for a relationship with a stored memory and if we don't have it, we invent it. Depending on the type of memory evoked, the mood may change or remain unchanged.. This is what happens to us when we evoke memories of our childhood, of nature, of the perfume of a person we met, and so on.

The effect is so powerful that our brain does not distinguish between the real situation and the evoked situation thanks to the olfactory effect. If the perceived smell is not associated with any memory, the experience of that moment will mark whether that instant in the future will be associated with a positive memory, a dangerous situation, a sad situation, etc.

All this, of course, happens in our brain automatically and unconsciously, without the direct participation of our conscious attentionThe rhinencephalon and other associated biological structures take care of this in a discreet manner. In many cases, from that moment on, that particular smell or aroma will be the one that motivates our future actions and the one that generates our acceptance or rejection of the circumstances associated with it.

Bibliographical references:

• Triviño Mosquera, M.; Bembibre Serrano, J.; Arnedo Montoro, M. (2019). Neuropsychology of perception. Madrid: Síntesis.