Final answer:
Chemoreceptors in the tongue and nasal passages respond to molecules dissolved in the air and relay that message to neurons in the olfactory bulb and olfactory cortex.
Step-by-step explanation:
Chemoreceptors respond to certain chemicals. They are found mainly in taste buds on the tongue, where they are needed for the sense of taste; and in nasal passages, where they are needed for the sense of smell. Olfactory receptor cells in the nasal passages have hair-like extensions that interact with chemical receptors when odor molecules are dissolved in the mucus. These receptors then send signals to the olfactory bulb and eventually to the olfactory cortex in the brain.