Neuroscience Resources for Kids

The NoseKnows

The smells of a rose, perfume, freshlybaked bread and cookies...these smells are all made possible because ofyour nose and brain. The sense of smell, called olfaction, involves the detection and perception ofchemicals floating in the air. Chemical molecules enter the nose anddissolve in mucous within a membrane called the olfactoryepithelium. In humans, the olfactory epithelium is located about 7cm up and into the nose from the nostrils.

The OlfactorySystem
Hair cells are the receptors in the olfactory epithelium that respond toparticular chemicals. These cells have small hairs called cilia on oneside and an axon on the other side. In humans, there are about 40million olfactory receptors; in the German Shepherd dog, there are about 2 billion olfactory receptors.
It is really unknown what actually causes olfactory receptors to react -it could be a chemical molecule's shape or size or electrical charge. Theelectrical activity produced in these hair cells is transmitted to theolfactory bulb. The information is then passed on to mitral cells in the olfactory bulb.
The olfactory tract(cranial nerve I) transmits the signals on to the brain to such areas asthe olfactory cortex, hippocampus, amygdala, and hypothalamus. Many ofthesebrain areas are part of the limbic system. The limbic system is involvedwith emotional behavior and memory. That's why when you smell something,it often brings back memories associated with theobject.
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 carrysmell cannot reach the olfactory receptors.

Did youknow?

About 2 million people in the United States have NO sense of smell.This disorder is called anosmia. A serious headinjury can cause anosmia. Most likely this results in damage to theolfactory nerves as they enter the olfactory bulb. It is also possiblethat damage of the frontal lobes caused by a tumor or surgery can causeanosmia. Elderly people often have a reduced sense of smell.

Did youknow?
People can distinguish between 3,000 and 10,000 different odors.Of course, some odors are more easy to detect than others. Forexample, people arevery sensitive to the smell of green bell pepper - people can detectthis smell when it is mixed with air at only 0.5 parts per trillion!
Here is one more fact...1 in 1,000 people are insensitive to butylmercaptan, the stinky smell of skunks.