Senses Primer Part 3: Smell

I’m currently traveling in Thailand right now, and one of the unique things Thailand is known for is its durian. Durian is a fruit that has a very particular smell. It’s akin to a rotten mango, and I’m a huge fan of it. It’s an acquired taste.


Your sense of smell is extremely underrated. This is partly because humans don’t have a good sense of smell relative to other animals. Humans have an aversion to sewage smell, and this trait evolved due to the unsanitary conditions of sewage. Smell is the source of flavor in food, and is a built-in alarm for danger and harm. 


Your sense of smell is the ability to detect chemicals within the air. In my opinion, smell is the most impressive trait due to its extreme variability. Vision is the ability to detect light, which is simplified to intensity and color. Hearing is the ability to detect sound, which is simplified to volume and pitch. There are a huge amount of chemicals, each with its own properties and differences. How do you simplify the differences between cinnamon, mint, and banana with a few variables? It’s not easy.



The current theory for chemical detection works like puzzle pieces. Each individual chemical has a bunch of shapes to it, and each olfactory receptor, the cells responsible for detecting chemicals, only detects a portion of the shape. The chemical detected depends on the specific pattern of olfactory cells that activate.



When these olfactory receptors activate, each of them point to a bunch of glomerulus cells. These glomerulus cells are responsible for specific concepts of smells. There exists a bunch of “cinnamon” glomeruli, “mint” glomeruli, and a “banana” glomeruli. When enough of the olfactory receptors from earlier converge signals onto a specific glomerulus, that glomerulus knows that it’s the smell being activated. The glomerulus sends a signal to a mitral cell, and these mitral cells send signals deeper within the brain. 


The intensity of the smell is dependent on how much of the chemical exists in the air. In olfactory bulb, there exists multiple of the same “flavor” of glomeruli. For example, your olfactory bulb has a bunch of “mint” glomeruli. If you detect a hint of mint in your dish, a few of your “mint” glomeruli will activate. If someone pushes you into a mint bush, a huge amount of your “mint” glomeruli will activate. This is how smell gauges intensity.


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