It’s often said that our most powerful sense is smell. This is because our ability to smell can evoke memories better than any of our other senses, making it the most delicate of them all. How often have you heard someone say that a particular smell reminds them of a family member or old friend? It’s because of this that people typically turn to scents when they’re feeling down.
When you think about it, this is perfectly logical. We rely on our noses to do so many different things, be it detecting dangerous substances or telling us how flavoursome a certain food is. Everyone’s sense of smell is unique, and this leads people to respond differently to particular smells in the air.
The reason that your sense of smell is so powerful is that your nose is able to transport molecules through its small openings. It can then detect them by using internal receptors, which is what gives us our perception of smell. Fundamental to understanding our sense of smell is the anatomy of the nose.
Consisting of two nostrils leading into separate tubes known as nasal cavities, the human nose is a complex thing. Within the cavities are tiny bumps called turbinate bones. These humidify and cleanse the air that enters your nose before it travels to your lungs.
What’s more, your cavity is comprised of a number of olfactory receptors, which are sensory cells that read the odours that you breathe in. Your cavities require mucus to carry out this function, which is why your body constantly produces it.
The cells in your nasal cavity produce the mucus, first in the form of a watery fluid that is released into mucus-producing glands, where it thickens. Next, hairline projections called cilia line the turbinate bones in your cavity, moving back and forth and causing you to swallow the mucus that has been formed.
When this process is complete, some of the smell molecules that were trapped within the mucus will be detected by the olfactory receptors. From here, a signal is sent to your brain, which interprets the scents as smells and memories, completing the complex process!
Introducing olfactory receptors
Olfactory receptors are clusters of neurons in the nose that are responsible for detecting smells. They send responses to the olfactory bulb via nerve tracts and brainstems. Humans are unable to see odours, but our nose is capable of detecting them and telling our brain how intense it is. In this respect, it’s helpful to regard an odour as a chemical message sent between organisms. In total, humans have approximately 400 different types of olfactory receptors, which detect smells from freshly baked bread to rotten garbage.
How are smells perceived?
The process of perceiving smells is known as retrograde transmission. Simply, this refers to the olfactory cells that travel to the brain via the nerve tract. The olfactory fossa is the pit that is home to our smell receptors, which exist with cilia on their surfaces. As molecules arrive into the pit, they are bound to particular proteins attached to receptor smells. Swiftly after this process, an electrical signal is fired up the olfactory nerve. The glomeruli within our brains then detect odour signals, which is where electrical impulses are transformed into neural impulses. It’s like a dashboard of signals, and it’s from here that the impulse is sent for smell identification.
Plant terpenes and the olfactory response
Our ability to smell is a curious thing. Plants have noticeable odours themselves, and the smells that they omit are often referred to as terpenes. Terpenes combine with olfactory receptors to improve the sense of smell and trigger responses in individuals. This is notable in people who suffer from conditions such as depression or panic attacks, as certain scents may evoke a particular reaction. For this reason, exposure to calming terpenes such as Myrcene or Linalool may benefit suffers from mental health conditions.
If you take a stroll in the great outdoors, you may smell the freshly cut grass or the wildflowers that surround you. In the past, this was thought to be due to the airborne particles that surrounded the plant. Today, however, we know that terpenes exist as an oil on the leaves of the plants. This is what triggers the reaction that many of us have when we smell certain things. Some scientists have posited that exposure to specific terpenes can influence serotonin levels in the brain.
Still, the precise way that terms trigger this response is not 100% clear, but the reactions can be both negative and positive. More than 30,000 terpenes exist, and they can be found everywhere, from pine needles to citrus fruits. When we were hunters and gatherers, our ability to sniff out food was part of our genetic code, and we were led by plant terpenes. The way the human nose works is fascinating, as it gives us an idea of what is around us. Without it, we would struggle to recognise our place in the environment, which would make our existence on the planet even more difficult.