Taste and Smell
Exercise 25
BI 232
Taste and Smell
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Both are examples of
chemoreceptors in
which specific chemical
compounds are detected
by the sense organs and
interpreted by various
regions of the brain
Gustation
Sensory receptors for
gustation are located in
taste buds
Located mainly on the top
of the tongue but also in
other areas of mouth
Innervated by cranial
nerves facial (VII),
glossopharyngeal (IX) and
Vagus (X)
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Taste Receptors
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Taste buds contain spindle-shaped cells
Basal cells: produce daughter cells that mature in
stages
Gustatory cells: extend microvilli into the surrounding
fluids through a taste pore
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Contain the taste receptors
Taste
Bud
Histology
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Taste Determination of Solid Materials
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Gustatory receptors are
stimulated by specific
chemicals in solution
Dry your tongue
Put some sugar crystals
on tongue
Keep mouth open
Can you determine what
the sample is?
Close mouth
Can you determine what
the sample is?
Gustatory Discrimination
1.
2.
3.
4.
5.
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Umami: “Beef”
Salty
Sweet
Bitter
Sour
Substances must be dissolved (saliva) for the
chemically gated ion channels to open
Olfaction is very important in taste
Mapping the Tongue for Taste Receptors
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We have varying degrees of sensitivity to the five tastes.
People with allergies, migraines or heart problems should
avoid the tasting of umami.
Select a dropper bottle labeled “sweet”, “sour”, “salty”,
“bitter” or “umami”
Use a sterile cotton-tipped applicator, apply one of the
tasting solutions to the cotton tip.
Dab the entire surface of your partner’s tongue
Map your tongue with all of the taste substances
Do not contaminate the solutions by reusing the
applicator sticks or use the same applicator stick
in different solutions
Olfaction
Sensory receptors for
olfaction are located in
the olfactory epithelium
consists of:
Olfactory receptor cells
Supporting cells
Basal cells
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Olfactory Reflex
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Take a small bottle of
ammonia and place it
under the nose of your lab
partner.
Have partner take a brief
sniff from the bottle.
If there is visible
movement of the head in
the posterior direction
then an olfactory reflex
occurred.
Visual Cues in Smell Interpretation
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Determine whether the
color of a substance has any
effect on what you perceive
the smell to be.
Lab partner shows you a
small vial labeled “almond”
and then smell it
Examine and smell the small
red vial labeled “Wild
Cherry”
Close your eyes and have lab
partner choose a vial for
you.
Can you tell which one it is?
Olfactory Discrimination
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Obtain four vials of
different scents
Peppermint, almond,
wintergreen and camphor
Lab partner closes their
eyes and try to determine
the name of each scent
Record how many of the
smells you got correct out
of the four.
Testing olfactory adaptation
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Adaptation refers to a
decreasing sensitivity to a
stimulus over time.
Sensitivity to an odor
diminishes over time.
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Adaptation to Smell
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Have partner close eyes and
plug one nostril
Inhale scent until the smell
degreases significantly
Have lab partner record
time it takes.
Now smell the wintergreen
or peppermint vial.
Does the adaptation of one
smell cause the olfactory
receptors to adapt to other
smells?
Taste and Olfaction Tests
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Demonstrates the dependence of the sense of smell on taste
Obtain 4 or 5 small cups
Label each with the name of the juice it will contain.
Pour juice into the labeled cups
Have lab partner sit with eyes and closed and nose plugged
Give samples of juice to partner
Partner should taste the sample and try to name it
Test all samples with nose closed and then open nose and
taste samples again
Record your results.
The End
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View Slide of taste buds
Make sure that you understand the tests performed in lab