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The smells of a rose, perfume, freshly baked bread and cookies...these smells are all made possible because of your nose and brain. The sense of smell, called olfaction, involves the detection and perception of chemicals floating in the air. Chemical molecules enter the nose and dissolve in mucous within a membrane called the olfactory epithelium. In humans, the olfactory epithelium is located about 7 cm up and into the nose from the nostrils.
The Olfactory System
Hair cells are the receptors in the olfactory epithelium that respond to particular chemicals. These cells have small hairs called cilia on one side and an axon on the other side. In humans, there are about 40 million olfactory receptors; in the German Shepherd dog, there are about 2 billion olfactory receptors.
No one knows what actually causes olfactory receptors to react - it could be a chemical molecule's shape or size or electrical charge. The electrical activity produced in these hair cells is transmitted to the olfactory bulb. The information is then passed on to mitral cells in the olfactory bulb.
The olfactory tract transmits the signals to the brain to areas such as the olfactory cortex, hippocampus, amygdala, and hypothalamus. Many of these brain areas are part of the limbic system. The limbic system is involved with emotional behavior and memory. That's why when you smell something, it often brings back memories associated with the object.
As you probably know, when you have a cold and your nose is stuffed up, you cannot smell very well. This is because the molecules that carry smell cannot reach the olfactory receptors.
Did you know?
For more information about the sense of smell, see:
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