The Science of Smell

Our sense of smell has garnered immense attention ever since losing it became a symptom of the #COVID19 disease. Read on to discover the fascinating science behind this sense of smell and how it is lost.

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Read About | Future of Biotechnology authored by Pooja S Madhavan

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Olfactory system, the system responsible for our sense of smell is quite a complex one encompassing the human anatomy, specific brain functions and a great deal of genes even though there exists a myth that animals have better olfactory senses.

The unique feature that sets our olfactory system apart from other senses is that the scent signals reach the regions of brain connected to memories and emotions. That is why certain scents are strongly associated with our memories and emotions.

The olfactory sensory neurons are located inside the nose which the smell can reach through either the nostril or the throat. The neurons then send signals to the olfactory bulb in the brain which in turn recognizes the smell.

The olfactory neurons are the odorant receptors i.e. they receive the odor molecules from the environment. They are G-protein coupled receptors which partake in the signal transduction process that is now well understood.

During the COVID-19 infection, sense of smell is lost because the odor molecules are unable to reach these receptors. Initially it was thought that the viral particles destroyed these neurons accounting to the sensory loss but later studies revealed that the olfactory neurons lacked the ACE2 receptors necessary for viral infection thus the neurons where unharmed. It was the supporting cells called ‘sustentacular cells’ that were affected. This led to swelling in the tissues that prevents the odor molecules from reaching the neurons. Hence the olfactory senses returned when the infection subsided.

However in some extreme cases, the loss is permanent. It has been speculated that it is because of what is called as inflammation, the immune system’s response to intruders where the neuronal receptors are also damaged in the fight.

The captivating question which now arises is how we have receptors for the countless odor molecules that exist in the environment? This is where the genetics come into play!

There are about 400 genes in the human genome which code for these olfactory receptors. However the natural variation present in the human population causes differences in the individual perception of smell. Even then how the receptors detect various molecules to help us identify over a trillion smells that we are capable of, is a mystery still being unraveled by the scientists.

Research in this arena is still capturing the interests of many scholars and for that we have Prof. Richard Axel to thank for, who set the ball rolling when he discovered how hundreds of genes code for these olfactory receptors, that too at a time when molecular biology was in its nascent stages. He won the Nobel Prize along with Linda Buck for his work on these olfactory receptor genes.

His birthday falls on 2nd July and we at Life Teck Research Centre commemorated his great contribution through our #CelebrateScientists series. Follow this hashtag for interesting insights into great scientific minds and their commendable works!

Pooja S Madhavan

Lead - Business Process and Planning

Life Teck Research Centre

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poojasmadhavan@lifeteck.net