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