Elizabeth Pell, age 12, of Billings, Mont., for her question:

HOW ARE ODORS DETECTED?

We detect smells by breathing or sniffing air that carrier odors. Odors come from molecules of gas that have been released into the air from amny different substances. There molecules stimulate receptor cells deep inside the nose.

The cells, which are part of the olfactory nerves, are on layers of mucus covered tissue. This tissue covers nasal bones called conchae. The receptor cells send the impulses created by the odor along the oflactory nerves.

The olfactory nerves then carry the impulses to a part of the brain called the olfactory lobe or olfactory bulb. From the olfactory lobe, the nerve impulses travel to the forebrain, the front part of the cerebrum of the brain. Here, the brain translates the nerve impulses it has received into information about the odor.

Scientists do not know exactly how different smells are distinguished.

One theory is that molecules of certain odors become more quickly and more strongly attached to the mucus at a particular place on the conchae than do other molecules.

According to this theory, an odor is distinguished by how fast and where its molecules become attached to the receptor cells.