An olfactory receptor is a small contact site on certain neural cells that is used for processing odorants. Odorants are chemical signatures that are shed by most substances and creatures. These molecular chemicals are more commonly referred to as "smells."

Many biologists hail the sense of smell as one of the most essential tools for the survival of any given organism. Indeed, nearly all living things, from simple invertebrates to man, have at least some amount of olfactory receptors. Fish, for instance, have approximately 100 varieties of these sites, whereas humans have around 10,000 of them. Nearly 3% of the human genetic code is devoted to the construction of the olfactory receptor.

A human being's sense of smell is extremely complex. It enables humans to discern factors concerning everything from the fitness and health of a potential mate, to identifying poisonous substances and edible food. It is closely connected to memory, in fact much more so than any other sense.

When a person ingests a food substance that is rotten or makes him sick, he retains that smell in his memory bank. When the odorant from that food or drink enters his nose, the olfactory receptors remind him of that incidence, and he are unlikely to eat or drink that substance again. This principle also extends to poisonous or helpful substances as well.

Try to imagine odorants as keys, and each olfactory receptor as a lock. Any given odorant will only bond to it's corresponding receptors, thus allowing a person to identify the smell. Often, one odorant will activate many receptors, as they are more attuned to properties of a substance than a substance itself.

This makes the sense of smell capable of identifying previously uncharacterized odorants. This is accomplished when the olfactory receptor translates the information from the odorant into neural pulses, which the brain then processes and categorizes. Olfactory receptors are so versatile that they are able to identify a near infinite combination of odors.

Millions of olfactory receptors are bundled into small groups at the back of the nasal cavity. These group to form the olfactory epithelium. Olfactory receptors are connected to the epithelium, which is covered in hairlike cilia. These cilia collect inhaled odorant molecules and send them to the olfactory receptors. Mucus that lines our nose and sinuses also helps to trap these odorants, enabling them to be processed.