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It smells quantastic, doesn't it?

It Smells Quantastic, Doesn’t It?

An Anatomical-Physiological Exploration

Schematic overview of the anatomy of the olfactory system.

Fig. 1. Schematic overview of the anatomy of the olfactory system. (Source: Oregon State University).

In fact, there are two pathways for odorant molecules to reach the receptors: through the nostrils, and via the channel that links up the upper part of the throat to the nasal cavity. The aromas that are released while chewing our food follow the latter pathway.

It Is All About Chemistry

A schematic view of the membrane depolarization process for olfactory receptor cells.

Fig. 2. A schematic view of the membrane depolarization process for olfactory receptor cells. (Source: Book “Neuroscience: Exploring the Brain, Enhanced Edition”).

This flip of charge polarity induces subsequently the creation of electrical signals (action potentials), which are transmitted through the olfactory tract to the olfactory bulb in the brain for further processing.

Who Holds the Key?

An anomaly of the shape theory: two similarly shaped compounds produce different odours.

Fig. 3. An anomaly of the shape theory: two similarly shaped compounds produce different odours. (Source: guidechem).

As a result, a newer version of the original theory, i.e. the docking theory, has hypothesized that, though odorants might acquire similar shapes and sizes, the distinctive smell originates from the brain decoding the different combinations in which the weak intermolecular forces, such as Van der Waals forces, hydrogen bonding, or electrostatic forces, act between the molecule and the receptor.

Smelling Vibrations

The musk odorant molecule cyclopentadecanone.

Fig. 4. The musk odorant molecule cyclopentadecanone. The grey balls refer to carbon atoms, the smaller white ones to hydrogen atoms, and the red one to an oxygen atom. For the experiment, the (undeuterated) hydrogen atoms would be replaced with a heavier hydrogen variant, i.e. deuterium (not presented in the image). (Source: pubchem).

Left: The classical view on activation energy and enzymes in chemical reactions. Right: the concept of quantum tunneling.

Fig. 5. (a) The classical view on activation energy and enzymes in chemical reactions, (b) the concept of quantum tunneling enables reactions to occur below the enzymatic energy threshold. (Source: adapted from blissbiology and lumenlearning).

The molecular structure of the mirror-image molecules limonene and dipentene.

Fig. 6. The molecular structure of the mirror-image molecules limonene and dipentene. In limonene, the lower chemical substructure comes out at the other end of your screen, whilst in depentene it comes out of your screen towards you. (Source: Paper Chukwuemba Asogwa).

All Is Well That Smells Well


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  1. Hi Olivier. Just a quick comment to let you know that I have nominated you for the Sunshine Blogger Award. You can read my post here: https://richiesroom.com/sunshine-blogger-award/

  2. Hi Olivier. Another excellent article – thank you. I have an interest in scent detection but from a canine perspective. Have you ever looked into the canine side of scent? They leave us in the shade, that’s for sure!

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