Figure 4.4. Cross section of the olfactory system.Smell (or Olfaction)
Our sense of smell also depends on chemicals emitted by substances. Molecules of substances, hot
chocolate for example, rise into the air. Some of them are drawn into our nose. The molecules settle in a
mucous membrane at the top of each nostril and are absorbed by receptor cells located there. The exact
types of these receptor cells are not yet known, as they are for taste buds. Some researchers estimate that
as many as 100 different types of smell receptors may exist. These receptor cells are linked to the
olfactory bulb (see Fig. 4.4), which gathers the messages from the olfactory receptor cells and sends this
information to the brain. Interestingly, the nerve fibers from the olfactory bulb connect to the brain at the
amygdala and then to the hippocampus, which make up the limbic system—responsible for emotional