Taste and Smell

Exercise 25BI 232

Taste and Smell 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

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 Contain the taste receptors

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Taste Bud Histology

Taste Determination of Solid Materials 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?

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Gustatory Discrimination

1. Umami: “Beef”2. Salty3. Sweet4. Bitter5. 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 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 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 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 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 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 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 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 View Slide of taste buds Make sure that you understand the tests

performed in lab