Gustation and Olfaction
Post on 24-Feb-2016
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Gustation and Olfaction
A running nose!
Why Taste? Help distinguish safe from unsafe
◦Bitter, sour = unpleasant◦Salty, sweet, “meaty” (umami) =
pleasant
SaltServes critical role in water
balance (homeostasis)◦Needed by kidney◦Allows passive re-uptake of water
from urine into blood
SourMildly pleasant in small amountsLarger = more unpleasantWhy?
◦Can signal “bad” food Over-ripe fruit Rotten meat Spoiled food
◦Bacteria grow in such media
BitterAlmost completely unpleasant to
humansMany 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
SweetSignals presence of
carbohydrates in solutionHighly desirable (high calorie
content due to large number of bonds)
Some non-carbohydrate compounds also trigger sweet sensation◦Saccharin,◦Sucralose, ◦Aspartame
Umami (Ooh-mommy)Signals presence of amino acid L-
glutamateEncourages intake of peptides and
proteins◦Used to build enzymes, ◦proteins in body
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…
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
Taste as ChemoreceptionTaste cells, contained in bundles
called taste budsContained in raised areas called
papillaeFound across tongue
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
Carried to brain, interpretedSensation carried via one of three
nerves:◦Facial (VII)◦Glossopharangeal (IX)◦Vagus (X)
OLFACTIONSense of Smell:
OlfactionSense of smellSpecialized sensory cells in nasal
cavityDetects volatile (airborne)
compoundsSupplement to taste…
Olfactory receptor neuronsExpress only one functional odor
receptorLike a “lock and key” – 500-
1000+ “locks”◦Each receptor binds with particular
odorant
Vomeronasal glandStructure at base of nasal cavityThought 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!
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
Olfactory EpitheliumProportion of olfactory to
respiratory epithelium (not innervated) indicates an animal's olfactory sensitivity. ◦Humans: 1.6 in2 olfactory epithelium◦Some dogs 26 in2.
Dog's olfactory epithelium also more densely innervated, (100 x’s more receptors/cm2)
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 contains
mucopolysaccharides, salts, enzymes, and antibodies ◦Very important - olfactory neurons provide
a direct passage for infection to pass to the brain
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