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Smell, like taste, is a chemical sense. We smell something when molecules of a sub-
stance carried in the air reach a tiny cluster of receptor cells at the top of each nasal cavity
TEACH 1.6-14 (Figure 1.6-24). By sniffing, you swirl air up to those receptors, enhancing the aroma. These
20 million olfactory receptors, waving like sea anemones on a reef, respond selectively — to
Enrichment the aroma of a cake baking, to a wisp of smoke, to a friend’s fragrance. Instantly, they alert
Ask students if we can tell whether a the brain through their axon fibers.
person is male or female on the basis Olfactory bulb
of odor alone. The following research 4. The signals are transmitted
studies indicate that we can: to higher regions of the brain.
Olfactory nerve
• Patricia Wallace had blindfolded
participants sniff a thoroughly Olfactory bulb 3. The signals are relayed
via converged axons.
washed hand, held ½ inch from Receptor cells
their nose. They could discriminate in olfactory Bone
membrane
male from female hands with more Olfactory
than 80 percent accuracy. Female receptor 2. Olfactory receptor
cells
sniffers were more accurate than cells are activated and
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
send electrical signals.
male sniffers.
• Richard Doty and his colleagues Odor molecules
had college students assess
breath odor of participants who 1. Odorants bind
to receptors.
sat on the other side of a partition
and exhaled through a plastic Odorant
receptor
tube. Most judges scored better Air with odorant molecules
than chance, and again females
outperformed males.
Figure 1.6-24
• Mark Russel had first-year college The sense of smell
students wear T-shirts for 24 Olfactory receptor cells send messages to the brain’s olfactory bulb, and then onward to the temporal lobe’s primary smell cortex and to the parts
of the limbic system involved in memory and emotion.
hours, after which the shirts were
individually placed in sealed TRY THIS Being part of an old, primitive sense, olfactory neurons bypass the brain’s sensory
containers. Each participant Copyright © Bedford, Freeman & Worth Publishers.
control center, the thalamus. Eons before our cerebral cortex had fully evolved, our mam-
Impress your friends with your new
was then presented with three word for the day: People unable to malian ancestors sniffed for food — and for predators. They also smelled molecules called
see are said to experience blindness.
containers: one holding their own People unable to hear experience pheromones — olfactory chemical messages — especially those secreted by other members
of their species. Some pheromones serve as sexual attractants. When straight men smelled
deafness. People unable to smell
shirt, a second holding the shirt experience anosmia. The 1 in 7500 ovulating women’s T-shirts, the men became more sexually interested and experienced
of an unknown female, and a third people born with anosmia not only increased testosterone (Miller & Maner, 2010, 2011).
have trouble cooking and eating,
Odor molecules come in many shapes and sizes — so many, in fact, that it takes many
holding the shirt of an unknown but also are somewhat more prone different receptors to detect them. A large family of genes designs the 350 or so receptor
to depression, accidents, and
male. The vast majority were able relationship insecurity (Croy et al., proteins that recognize particular odor molecules (Miller, 2004). Linda Buck and Richard Axel
2012, 2013). Loss of smell and
to identify their own shirt and taste have been commonly reported (1991) discovered (in work for which they received a Nobel Prize in 2004) that these receptor
which other shirts belonged to a symptoms of Covid. proteins are embedded on the surface of nasal cavity neurons. Just as a key slips into a lock,
odor molecules slip into these receptors. Yet we don’t seem to have a distinct receptor for each
male or female. detectable odor. Odors trigger combinations of receptors, in patterns that are interpreted by
150 Unit 1 Biological Bases of Behavior
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150 Unit 1 Biological Bases of Behavior
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