Taste and Smell Exercise 25 BI 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) 3

4 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

5 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?

7 Gustatory Discrimination 1. Umami: “Beef” 2. Salty 3. Sweet 4. Bitter 5. 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 9

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. 13

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