Have you ever wondered how our noses detect smell? Detecting smell is a complicated process, but it has a large impact on our lives; our sense of smell can help us sniff out freshly baked cookies in the oven, but it can also protect us by allowing us to detect dangerous situations like a fire.
We can detect smells because of the chemical compositions of the objects around us. At a basic level, when these chemicals reach receptors in the nose, the brain can process these chemical signals and detect smell. A common misconception is that the nostrils are useful in detecting smell, but in reality, the nostrils are only the entryway for the vaporized molecules of chemicals. After passing through the nostrils, these molecules land on the back of our noses on a structure called the olfactory epithelium. The olfactory epithelium is a mucus-covered tissue that contains many olfactory receptors; these receptors are able to bind very specifically to odor molecules (odorants). The specific binding sets off a chain of electrical impulses which travel to the brain and help determine exactly what you’re smelling! The function of these receptors and their specificity was discovered and studied by Richard Axel and Linda Buck at Columbia University; their research won them the Nobel Prize in Physiology or Medicine in 2004.
Image Source: Betsie Van der Meer
When the receptors in the epithelium are activated, an electrical signal is generated in the sensory neurons in the olfactory epithelium. This signal travels to the olfactory bulb at the base of the forebrain (right above the eyes), where the signal is further propagated to other areas of the brain for processing.
Various parts of the brain are used to process smell. For example, the piriform cortex is involved in distinguishing between different smells. The thalamus can send some of the information from the olfactory epithelium to the orbitofrontal cortex, allowing the sense of smell and taste to be integrated. In fact, when we eat something, we often assume that the only form of sensory input is taste. In reality, these sensory inputs are a result of a combination of both smell and taste.
Our sense of smell is an important part of our lives. In fact, our nose is capable of detecting at least one trillion different smells, making our sense of smell more impressive than other senses like sight (several million colors detectable) or sound (approximately 500,000 tones detectable)! Understanding how the olfactory system functions can help us better understand the importance of the sense of smell in our everyday lives.
Feature Image Source: Super Nose by montillon.a