The next time you stop to smell the roses, take a moment to consider how you are able to enjoy their perfume. Sniff the velvet petals, and a cocktail of aromatic molecules wafts across odor receptors within your nasal cavity. Each is located on an olfactory neuron that extends into the brain. Chemical compounds that tumble past will bind to and activate a variety of receptors and their neurons. Your brain decodes this pattern as the unmistakable fragrance of a rose.
— From On the Scent of Smell, which discusses recent work by John Ngai, Coates Family Professor of Neuroscience and Director of the Functional Genomics Laboratory at UC Berkeley. Many thanks to Mary for the link!