Bill Nye the Science Guy - Season 5 Episode 11
Smell

How do noses work? Objects give off tiny amounts of tiny molecules into the air. When just a few of these molecules get up your nose, they dissolve in the mucus up there. Some molecules come into contact with special receptors on what’s called your “olfactory membranes.” Each nostril has a membrane, and each membrane is only about the size of a postage stamp. The membranes hold millions of receptor cells, each of which are ready to send messages to the brain about the molecules that go up your nose.