Olfaction, the power sense.
Smell is one of the five senses that humans have. Thanks to the nose, we can feel all kinds of sensations: the most delicious as well as the most unpleasant. The nose allows us to analyze our environment. It acts a bit like an alarm system: the smell of food will whet our appetite, while the smell of smoke will warn us of danger.
The nose is the organ of smell. The sensory function of olfaction allows the perception of odorous substances, through the olfactory mucosa, which lines the inside of each nasal cavity, with a variable surface area of approximately 3 to 5 cm².
Only substances in a gaseous state can be odoriferous and recognizable by smell.
What is the physiological mechanism of olfaction?
An odorous product that enters the nose only becomes an “odor” if it is detected by the olfactory mucosa. It is the only nerve tissue directly exposed to the air. The olfactory mucous membrane is composed, among other things, of neurons, which transform the chemical message into nerve impulses that can be interpreted by the brain.
Olfactory neurons ensure the reception of odorous molecules which are “inspired” into the nasal cavity and reach the olfactory mucosa. These neurons are equipped with molecular olfactory receptors. Although there is a wide variety of receptors, each neuron carries only one variety of receptors.
Once “fixed” at the level of a receptor, the odorous molecules will trigger one or two cascades of chemical reactions inside the neuron. The signal is then sent to the olfactory bulb. The olfactory bulb is a small structure located on the floor of the skull that processes the olfactory message coming from the nasal cavity.
From the olfactory bulb, olfactory information is transmitted to 2 different systems:
- The conscious system: the place of rational perception, that is to say the identification of odors.
- The limbic system: the birthplace of emotions, memory activation, instinctive behaviors (food, defense, sexual…), it regulates vegetative functions (heart, breathing)…
There is therefore a privileged anatomical link between olfaction, memory and emotion.
Although humans are less dependent on chemosensory inputs than other mammals, olfactory function still plays a critical role in health and behavior.
Smells change behavior, revive memories
Olfactory memory stands the test of time better than other memories. Indeed, the sense of smell is a particular sense which offers the advantage of allowing a smell to bring up an emotional memory, kept intact in our limbic system.
In a hospital environment, in people suffering from amnesia or in people who are in a coma, effective rehabilitation consists in reviving the memory by smelling familiar smells, well known in the past. The olfactory memory records all the context related to an event and through the many neural connections between sight, hearing and smell, the memory is re-educated.
The stimulation of the olfactory pathways through essential oils, and particularly the limbic nervous system, can also give a set of effects, which can manifest themselves in the physiology, behavior, feelings and moods of people.
The sense of smell in a few figures
- 1000 billion different smells could be distinguished.
- 400 different olfactory receptors: for comparison, the eye with its 3 different receptors sees 10 million colors.
- 45 days: the average lifespan of olfactory cells.
- 3cm², the surface of the olfactory mucosa.
The principle of olfactotherapy
The sense of smell being directly linked to memory and emotions, a smell, whether pleasant or unpleasant, will therefore directly influence behavior and emotions.
Essential oils, fragrant principles par excellence, therefore have a place of choice in care by smell. Olfactotherapy or aromachology is therefore a therapy that uses the smells of certain essential oils to calm, tone, release and regulate emotions. The multiple olfactory molecules present give them numerous properties when diffused. They are therefore used as messengers to deliver information very quickly to the limbic system, which is the seat of emotions and pleasure.
To benefit from all the benefits of olfactotherapy, it is important to take into account the olfactory pyramid of a composition, to use the appropriate diffusion system and to learn to smell essential oils well.
The importance of the olfactory pyramid for an effective composition
The olfactory pyramid is made up of notes that are representative of the degree of evaporation of an olfactory composition, they are ideally complementary and inseparable.
Top Notes: They are noticeable immediately after applying the scent. They come from the most volatile substances. We generally find all citrus fruits, certain flowers such as lavender, aromatics such as rosemary, bay leaf, thyme and marine notes. These notes are of low tenacity from 0 to 2 h.
The Heart Notes: They come next and develop for several hours (up to 5 hours). They are the characteristic smell of symbiosis. We find almost all the floral notes (jasmine, rose…), most of the spices (cloves…), fruits and certain woods (rosewood).
Base Notes : They are the slowest to evaporate, they can last up to 24 hours. Their essential role is to make the smell of the olfactory composition last. You can find almost all resins (benzoin), balms, woods and vanilla.
An essential oil belongs to a single olfactory family while a composition with several essential oils is represented by the different olfactory families. A balanced pyramid allows to have an optimal action on the olfactory receptors.
The path to wellness
To make the most of the virtues of olfactotherapy, it is important to pay attention to the smells that surround us. This awareness helps us to develop our sense of smell and thus be more receptive to the scents that touch our nose. The world of smell is that of the inner world, so it is advisable to disregard the outer world as much as possible in order to focus on the perceived scent. When we breathe in the scent of an essential oil, we obtain a well-being corresponding to the effects of this oil.