Download The Chemical Senses: Smell and Taste How does the nose and

The Chemical Senses:
Smell and Taste
How does the nose and tongue work?
Olfaction (smell) detects chemicals that
are airborne.
Gustation (taste) detects chemicals in
solution that come into contact with
receptors inside the mouth.
There are animals without vision, and
there are some without hearing, but there
are no animals without some form of
chemical sense.
Humans have about 9 million olfactory
neurons, whereas there are 225 million
olfactory neurons in dogs.
Dogs and many other species can detect
pheromones (chemicals released by an
animal that can cause behavioral and
physiological changes in another animal)
Pheromones in humans?
Recent research suggests that humans
have the physiological capacity to
respond to pheromones.
Pheromones can influence the secretion
of certain hormones and can produce
physiological changes related to
reproduction.
This is one reason why women who live
together tend to menstruate at the same
time.
Steps in olfaction:
1. Chemicals reach the olfactory area through the nostrils and the
back of the mouth.
2. Fibers pass directly from the olfactory area to the olfactory bulb
in the brain.
3. From the olfactory bulb, signals travel to the hypothalamus and
amygdala.
Olfactory Bulb
Substances with similar chemical structures have
similar odors.
In contrast to vision, (four basic kinds of receptors)
olfactory system uses about 1,000 kinds of receptors.
Humans can detect tens of thousands of different
odors!
Smell and Emotions
Smell is the only sense that does not
send messages through the thalamus.
Connections from the olfactory bulb are
spread through out the brain and are
especially plentiful in the amygdala.
Research has shown that associations
between a certain experience is not
weakened over time (Lawless and Engen,
1977) and odors can bring back accurate
memories of significant experiences
linked with them (Engen, Gilmore and
Mair, 1991)
Taste
The human taste system can detect four basic tastes:
sweet, salty, bitter, and sour.
Papillae (bumps on your tongue) contain taste buds. The
average person has 10,000 taste buds.
Smokers and elderly people have fewer taste buds.
Each taste bud contains about 100 taste
receptors.
About 25% of the population are
“supertasters” -- because they have an
especially large number of papillae on
their tongues.
Sensory Interaction
When you have a stuffy nose it is more
difficult to taste your food. Why?
Smell and taste pathways converge. Your
taste receptors and olfactory receptors
are responding to the same chemicals and
combine to form the flavor of a food.
The smell and taste pathways converge in
orbitofrontal cortex (a.k.a. the flavor
cortex)
The sight and texture of food can also
affect the flavor.