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the upper nasal passage. The olfactory receptor cells are topped with tentacle-like protrusions
that contain receptor proteins. When an odor receptor is stimulated, the membrane sends neural
messages up the olfactory nerve to the brain (see Figure 4.31 "Smell Receptors").
Figure 4.31 Smell Receptors
There are more than 1,000 types of odor receptor cells in the olfactory membrane.
We have approximately 1,000 types of odor receptor cells (Bensafi et al., 2004), [4] and it is
estimated that we can detect 10,000 different odors (Malnic, Hirono, Sato, & Buck,
1999). [5] The receptors come in many different shapes and respond selectively to different
smells. Like a lock and key, different chemical molecules “fit” into different receptor cells, and
odors are detected according to their influence on a combination of receptor cells. Just as the 10
digits from 0 to 9 can combine in many different ways to produce an endless array of phone
numbers, odor molecules bind to different combinations of receptors, and these combinations are
decoded in the olfactory cortex. As you can see in Figure 4.32 "Age Differences in Smell",
women tend to have a more acute sense of smell than men. The sense of smell peaks in early
adulthood and then begins a slow decline. By ages 60 to 70, the sense of smell has become
sharply diminished.