Gustation and Olfaction

1. Gustation and Olfaction A running nose!

2. Why Taste? • Help distinguish safe from unsafe • Bitter, sour = unpleasant • Salty, sweet, “meaty” (umami) = pleasant

3. Salt • Serves critical role in water balance (homeostasis) • Needed by kidney • Allows passive re-uptake of water from urine into blood

4. Sour • Mildly pleasant in small amounts • Larger = more unpleasant • Why? • Can signal “bad” food • Over-ripe fruit • Rotten meat • Spoiled food • Bacteria grow in such media

5. Bitter • Almost completely unpleasant to humans • Many nitrogenous organic compounds (with pharmacological effect) have bitter aftertaste • Caffeine (coffee) • Nicotine (cigarettes) • Strychnine (pesticides) • Signals possible poison, spoilage of food to body… cause gagging at high concentrations

6. Sweet • Signals presence of carbohydrates in solution • Highly desirable (high calorie content due to large number of bonds) • Some non-carbohydrate compounds also trigger sweet sensation • Saccharin, • Sucralose, • Aspartame

7. Umami (Ooh-mommy) • Signals presence of amino acid L-glutamate • Encourages intake of peptides and proteins • Used to build enzymes, • proteins in body

8. Taste map? • It’s a myth! (And a mistranslation of a German research paper) • Concentrations of taste buds do change from one area to the next…

9. Supertasters? Is it a good thing? • 15-25% of the population has more papillae (and taste buds) than the rest of us… • Supertasters turn up their noses at bitter but nutrient-rich veggies such as broccoli and kale. • This group more likely to have precancerous colon polyps than people with a below-average number of taste buds

10. Taste as Chemoreception • Taste cells, contained in bundles called taste buds • Contained in raised areas called papillae • Found across tongue

11. Debated whether taste cells can respond to one or many “tastants” • Brain may be interpreting “patterns” of larger sets of neuron responses • Saliva helps dissolve tastant molecules so they can bind to receptors in taste buds

12. Carried to brain, interpreted • Sensation carried via one of three nerves: • Facial (VII) • Glossopharangeal (IX) • Vagus (X)

13. Sense of Smell: Olfaction

14. Olfaction • Sense of smell • Specialized sensory cells in nasal cavity • Detects volatile (airborne) compounds • Supplement to taste…

15. Olfactory receptor neurons • Express only one functional odor receptor • Like a “lock and key” – 500-1000+ “locks” • Each receptor binds with particular odorant

16. Vomeronasal gland • Structure at base of nasal cavity • Thought to sense body chemicals associated w/ sexual behavior (phermones) • Debated still… • Lack of nerve structures innervating this “gland” • Has been demonstrated to help distinguish body odor differences in men and women!

17. Several theories on how this works: • Shape theory – • Each receptor detects a feature of the odor molecule • Weak shape theory • Different receptors detect only small pieces of molecules; inputs combined to form larger perception • Vibration theory • Odor receptors detect the frequencies of vibrations of odor molecules in the infrared range by electron tunneling

18. Olfactory Epithelium • Proportion of olfactory to respiratory epithelium (not innervated) indicates an animal's olfactory sensitivity. • Humans: 1.6in2 olfactory epithelium • Some dogs 26in2. • Dog's olfactory epithelium also more densely innervated, (100 x’s more receptors/cm2)

19. Molecules of odorants pass through nasal concha of the nasal passages • Dissolve in the mucus lining • Detected by olfactory receptors on dendrites of the olfactory sensory neurons. • May occur by diffusion or by the binding of the odorant to odorant binding proteins. • Mucus on the epithelium containsmucopolysaccharides, salts, enzymes, and antibodies • Very important - olfactory neurons provide a direct passage for infection to pass to the brain