Physiology: Animal Function and Reproduction
How do animals and people identify smells?
The sense of smell allows animals and humans, as well as other organisms, to identify food, mates, and predators. This sense also provides sensory pleasure (for example, of flowers) and warnings of danger (for example, of chemical dangers). Specialized receptor cells in the nose have proteins that bind chemical odorants and cause the receptor cells to send electrical signals to the olfactory bulb of the brain; from there, the cells in the olfactory bulb relay this information to olfactory areas of the forebrain to generate perception of smells.
And when it comes to the ability to smell, humans are not as good as other animals. For example, a bloodhound has about 300 million scent receptors in its nose; a human has a mere five million. To compare, it is often said the human has the scent receptors the size of a postage stamp, whereas the bloodhound has one the size of a handkerchief.