Have you ever wondered how we know how something smells? I mean, the volatile molecules entering your nose have to tell your brain in one way or another: “Hey, it’s me!”.
But how do these messages get up there in the first place?
To find the answers to these questions, we need to turn to chemical messaging and electrical signaling between our nose and brain as well as within our brain. Most intriguingly of all, it seems that we invoke ideas from quantum physics to enable signals to get to our brain.
Let us break down all of this step by step.
An Anatomical-Physiological Exploration
Our sense of smell — called olfaction — is designed to serve multiple purposes: detect danger, identify food when hungry, increase our chances of reproduction, or avoid consuming toxic or spoiled substances. And our nose has physically evolved to optimize these functions.
About 7 cm (2.8 inches) above and behind our nostrils, we come across an air-filled space — the nasal cavity — that contains a tissue, i.e. the olfactory epithelium, in which plentiful odour receptors are planted. We have by estimation 50 million of these receptors.
Towards the base of the epithelium, the receptors have grown extensions (dendrites) which are embedded in a layer of mucus — the hair-like endings are referred to as olfactory cilia. This is the place where incoming particles (odorant molecules) will be picked up.
Odorants from, say, a fresh peppermint tea end up in our nasal cavity, integrate into the mucus, and stimulate certain odour receptors.
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.
Higher up inside the epithelium, each receptor cell is connected to just one olfactory sensory neuron. These nerve cells are in turn extended via the olfactory tract into the brain, namely…