The Biology behind Smell

Have you ever thought about how odor and smell gets detected by our bodies? 
It's a mechanism or an organ system within us linked to the nose, mouth and brain like a coordinated entity that just doesn't smell but also connects the dots between the past memories and present real-time scent. 

Firstly, when you take a whiff of perfume like a hidden gem on the shelf after quite a while- those odor molecules transport through the nose to get trapped by the mucus lining on our olfactory epithelium with cilia which are hairy-like bristles and it's this olfactory mucosa with approximately ten million olfactory neurons that detects the perfume molecules. The olfactory bulb is the one which processes the olfactory identity. 

Each olfactory neuron has a unique shape that accommodates only one single type of receptor even varying by spatial orientation. So, let's say this perfume has limonene in it so we have two enantiomers of limonene which are basically mirror images that can't be superimposed but when we smell both these enantiomers individually- they both have a different scent and that's because the spatial orientation in its geometry fits in only one type of neuron like D-limonene fits in only one type and L-limonene fits differently in another type. 

After they fit, it sets this buzz in different G-protein coupled receptors which electrify and activate an enzyme called Adenylate Cyclase and then this signal is fired to the brain. The neurons bundle up axons that pass through the cribriform plate sieve and the glomeruli are these small spherical clusters that sort out the the smells to decipher them.

So, once it reaches the brain- there's a chain of organs and parts- it travels through piriform cortex which is a pear-shaped region that helps us emulate which object it is like if you smell a citrusy perfume- you would get an idea of an object in your head like a lemon or maybe bergamot. Then comes the amygdala which regulates the activities of the hippocampus and orbitofrontal cortex. It's the seat of emotions and hedonic value which also is helped by the insular cortex in sensory integration. The amygdala is like the response center of the scent like is it something you love or despise. 

The hippocampus is like the DVD center of the head with all the tapes of memories we've inculcated throughout our lives like a tunnel of videos recorded and kept in this little library. The entorhinal cortex is the librarian who picks up the DVD from the hippocampus and then gives you this certain link or connection like when you smell that citrusy perfume you've worn before and suddenly it takes you back to a summer beach sunset because of that mist of bergamot shimmering like a sauntering star. 

Then comes the orbitofrontal cortex, a fascinating seat of imagination, cognitive decision making, awareness and pleasure. It makes us spark up as well- closely linked with the dopaminergic system that gives us this sense of reward by smelling it- a smile or a repulse. 

Smell is such a magical sense because it's the only one which doesn't transmit through the thalamus and it goes directly to the limbic system instead which gives us this instant sense of emotion and feeling. The olfactory neurons are constantly bugged by bacteria, fungi, viruses and pollutants in the air and hence are one of the rare type of neurons that get replaced by basal stem cells constantly and have a limited life span of 30-60 days.

So, when you smell that whiff- you're aware of that bergamot scent watching the sunset you had once before and you can feel a bittersweet spark of evanescence as the wind blows, suffusing that fever dream through the scent molecules flitting like pretty songbirds. 

So, all the time taken right from processing the olfaction to detection to perceiving the smell and getting aware of it takes 1 second!
And also when we chew food, the aroma molecules of our food go via the passage at the very end of our mouths resulting in retro-nasal olfaction which depicts how flavor and fragrance are intricately criss- crossed together. 

The mechanics of scent are very intricate processes, occurring in fractions of time like a magical wand spiraling in the symphony of a perfume.

Every part of this olfactory system just doesn't detect it but also underscores the notes and art behind the perfume- a beautiful potion that poisons us within a shawl of smiles or a tryst with tears.