That the odor of any substance is determined by the structure of its molecules is generally accepted. These, on arriving at the olfactory clefts, interact with one or more types of receptors embedded in the olfactory epitheliums. This triggers a series of molecular and cellular events that result in nerve impulses being sent from the olfactory bulb to the brain. The end result of this process is the subjective experience of smell (Amoore et al., 1964).
It is known that the sensation of colour arises from the stimulation of three distinct types of visual receptors. Each preferentially absorbs light of certain wavelengths, corresponding to one primary colour sensation (red, green, or blue), Therefore, one may ask analogous questions concerning smell:
l How many different types of olfactory receptors are there?
l To what primary odors do these correspond?
l What are the molecular characteristics required for stimulation of each type of olfactoy receptor?