Smell

How does your sense of smell work?

Your sense of smell—like your sense of taste—is part of your chemosensory system, or the chemical senses.

Your ability to smell comes from specialized sensory cells, called olfactory sensory neurons, which are found in a small patch of tissue high inside the nose. These cells connect directly to the brain. Each olfactory neuron has one odor receptor. Microscopic molecules released by substances around us—whether it’s coffee brewing or pine trees in a forest—stimulate these receptors. Once the neurons detect the molecules, they send messages to your brain, which identifies the smell. There are more smells in the environment than there are receptors, and any given molecule may stimulate a combination of receptors, creating a unique representation in the brain. These representations are registered by the brain as a particular smell.

Smells reach the olfactory sensory neurons through two pathways. The first pathway is through your nostrils. The second pathway is through a channel that connects the roof of the throat to the nose. Chewing food releases aromas that access the olfactory sensory neurons through the second channel. If the channel is blocked, such as when your nose is stuffed up by a cold or flu, odors can’t reach the sensory cells that are stimulated by smells. As a result, you lose much of your ability to enjoy a food’s flavor. In this way, your senses of smell and taste work closely together.

Without the olfactory sensory neurons, familiar flavors such as chocolate or oranges would be hard to distinguish. Without smell, foods tend to taste bland and have little or no flavor. Some people who go to the doctor because they think they’ve lost their sense of taste are surprised to learn that they’ve lost their sense of smell instead.

Your sense of smell is also influenced by something called the common chemical sense. This sense involves thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth, and throat. These nerve endings help you sense irritating substances—such as the tear-inducing power of an onion—or the refreshing coolness of menthol.

Source: NIDCD (NIH)1

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Whether coffee brewing, pine trees in a forest, or smoke from a fire, the things we smell are actually tiny molecules released by substances all around us. When we breathe in these molecules, they stimulate specialized sensory cells high inside the nose. Each of these sensory cells has only one type of odor receptor—a structure on the cell that selectively latches onto a specific type of “smelly” molecule. There are more smells in the environment than there are odor receptors. But a given molecule can stimulate a combination of these receptors, creating a unique representation in the brain of a particular smell.

“It’s estimated that the number of odors that people can detect is somewhere between 10,000 and 100 billion, or even more,” says Dr. Gary Beauchamp, a taste and smell researcher at Monell Chemical Senses Center in Philadelphia. We all have different combinations of odor-detecting cells in our noses, he explains, so people vary greatly in their sensitivity to smells. “In fact, when you or I smell the same physical thing, our perceptions may be very different,” Beauchamp says.

Source: NIH News in Health (NIH)2

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Smell: The ability to detect scents or odors, such as the function of Olfactory Receptor Neurons.3

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References

  1. Source: NIDCD (NIH): nidcd.nih.gov/ health/ smell-disorders
  2. Source: NIH News in Health (NIH): newsinhealth.nih.gov/ issue/ aug2016/ feature1
  3. Source: MeSH (U.S. National Library of Medicine)

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.