Some people say that they feel a sense of smell is their most powerful sense. Others have said it’s their most delicate one, because smell evokes memories more than any other sense. People often talk about the way that certain smells remind them of home or a family member or an old friend, and for this reason many people use scents as a way to comfort themselves when they’re feeling down.This makes perfect sense if you think about how much we rely on our noses to do all sorts of things: from detecting dangerous substances in the environment to telling us what flavor food has by reading its aroma alone. Your nose also reacts differently to different people as well as to their own natural scents, something that is unique to every person.The power of the sense of smell is due in part to your nose’s ability to transport molecules through small openings and detect them with receptors inside. But how do we actually perceive smells? We’ll start by learning about the anatomy of the nose.The human nose has two nostrils that lead into slightly separated tubes, called nasal cavities. These cavities are lined with small bumps called turbinate bones, which swell and shrink as air enters them to help humidify and cleanse the air before it reaches into your lungs.The inside of each cavity has large numbers of olfactory receptors, which are sensory cells that detect odors as you breathe in. In order to do this, they require a constant supply of mucus– and as a result, you’re constantly producing it!The mucus is made by cells in the nasal cavity, which produce a watery fluid and release it into mucus-producing glands. The glands keep on adding more of their fluid to your nose’s mucus until it becomes really thick.Next, cilia — hairlike projections that line the turbinate bones — wave back and forth to push the mucus toward your throat so you can swallow it.Once this happens, some of the smell molecules that have been trapped in the mucus will spill into nearby olfactory receptors. These are then able to send signals through sensory neurons all the way up to your brain, which interprets these signals as smells– and in some cases, memories.What is an olfactory receptorOlfactory receptors, also known as olfactory cells or smell receptor cells, are clusters of neurons in the nose that detect odors. Olfactory receptor cells send responses to the olfactory bulb via brainstem and nerve tracts.An odor is a compound we cannot see but we can detect because our nose detects it and tells our brain what it is and how intense it is. You can think of an odor as a chemical messenger sent from one organism to another. We rely on our sense of smell both for survival and enjoyment. Humans have about 400 different types of olfactory receptors, each responding to different chemicals that give rise to smells ranging from flowers to rotten eggs.How do we perceive smellsWe perceive smells through a process called “retrograde transmission”, which means that signals from our olfactory cells travel back to the brain via nerve tracts and synapses instead of forward towards the nose.Smell receptors are olfactory neurons located in our noses with cilia on their surfaces inside concave pits called “olfactory fossa”. When molecules float into this pit, they bind to specific proteins that are attached to receptor cells, which then fire an electrical signal up the olfactory nerve.Odor molecules are detected by the glomeruli in our brains, where electrical impulses are transformed into neural impulses that are sent to other brain regions for identification of the exact smell . This is how we know that we just smelled a fresh lemon rather than a banana.How plant terpenes effect the olfactory responseThe sense of smell is an interesting thing. Although plants depend on them in order to survive, plants also have a very noticeable odor themselves. The smells that they release are called terpenes. And it turns out that these terpenes can have an effect on your olfactory response. Terpenes work with the olfactory receptors to enhance the sense of smell and trigger different responses in people who respond to certain scents. For example, people that suffer from panic attacks or depression – both of which are linked to an abnormal functioning of the olfactory system – may benefit from exposure to calming terpenes like Linalool or Myrcene.If you were to take a walk through a forest or even just open up some fresh cut grass, you would be able to smell the pine trees and wildflowers around you. Once upon a time, it was thought that this was due to airborne particles of the plant itself. But now we know better that terpenes actually exist as an oil on the surface of the leaves. Terpenes are responsible for triggering different reactions in different people. For example, some scientists believe that terpene exposure affects serotonin transport in the brain. They go on to explain that the smell of lavender reduces anxiety and tension while reducing cortisol levels. According to Vossen (2015), the smell of lavender has also been shown to have an effect on memory.The way in which terpenes actually trigger a response is still not clear even though it is known that they can cause reactions both positive and negative. There are over 30,000 different types of terpenes that exist. Some of them are present in pine needles while others can be found in citrus fruits like lemons and orangesBack when we used to hunt and gather for our food, this baked into our genetic code to use the sense of smell in order to find a good meal. Although it seems like magic, it really comes down to these plant terpenes!The human nose is one of the most interesting parts of being a sentient being. It’s an organ that gives us information about everything around us via smells and aromas. Without it, there are many things that we would be unable to detect or understand in our environment, making life on earth very different.