How We Smell
The olfactory system is a pretty amazing piece of machinery. According to current research, the human nose can theoretically distinguish about 1 trillion different scents. Sounds pretty impressive, but how do we get it done.
Olfaction, like taste, is one of the chemical senses. Due to the volatile nature of odorant molecules, we are able to smell something when our olfactory system comes into physical contact with a molecule in the air. When an air current sweeps an odorant up through the nostrils, the molecules hit the olfactory epithelium which occupies only about one square inch of the superior portion of the nasal cavity. Mucus secreted by the olfactory gland coats the epithelium's surface and helps dissolve the odorant molecules.
Olfactory receptor cells are neurons with knob shaped tips, called dendrites. When an odorant stimulates a receptor cell, the cell sends an electrical impulse through the axon at its base and into the olfactory bulb. Since there are many more odors than there are receptor cells (only about 400), it is the combination of receptor cells which respond to any aroma which allows us to distinguish one scent from another.