Download The Senses - Gustation and Olfaction

Gustation and Olfaction
Why Taste?

Help distinguish safe from unsafe
◦ Bitter, sour = unpleasant
◦ Salty, sweet, “meaty” (umami) = pleasant
Salt

Serves critical role in water balance
(homeostasis)
◦ Needed by kidney
◦ Allows passive re-uptake of water from urine
into blood
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
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
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
Umami (Ooh-mommy)
Signals presence of amino acid Lglutamate
 Encourages 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 Chemoreception
Taste cells, contained in bundles called
taste buds
 Contained in raised areas called papillae
 Found 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, interpreted

Sensation carried via one of three nerves:
◦ Facial (VII)
◦ Glossopharangeal (IX)
◦ Vagus (X)
Sense of Smell:
OLFACTION
Olfaction
Sense of smell
 Specialized sensory cells in nasal cavity
 Detects volatile (airborne) compounds
 Supplement to taste…

Olfactory receptor neurons
Express only one functional odor
receptor
 Like a “lock and key” – 500-1000+ “locks”

◦ Each receptor binds with particular odorant
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!
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 Epithelium

Proportion 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