Chapter 17: Special Senses (Taste) Flashcards
Sense of Taste
Or taste, is a chemical sense.
_______ is much simpler than olfaction in that only
five primary tastes can be distinguished: salty, sour,
sweet, bitter, and umami
GUSTATION
caused by the presence of sodium ions
(Na+) in food.
SALTY TASE
o caused b
________ is produced by hydrogen ions
(H+) released from acids. Lemons have a
sour taste because they contain citric acid.
Sour taste
elicited by sugars such as glucose,
fructose, and sucrose and by artificial
sweeteners such as saccharin, aspartame,
and sucralose
SWEET TASE
caused by a wide variety of substances,
including caffeine, morphine, and quinin
BITTER TASE
, first reported by Japanese scientists, is
described as “meaty” or “savory.”
o It is elicited by amino acids (especially
glutamate) that are present in food. This is
the reason why the additive monosodium
glutamate (MSG) is used as a flavor
enhancer in many foods.
UMAMI TASE
an oval body consisting of three kinds of
epithelial cells: supporting cells, gustatory
receptor cells, and basal cells.
Taste Buds
surround about 50 gustatory receptor
cells in each taste bud
Supporting Cells
(gustatory hairs) project from each
gustatory receptor cell to the external
surface through the taste pore, an opening
in the taste bud.
Gustatory microvilli
stem cells found at the periphery of the
taste bud near the connective tissue layer,
produce supporting cells, which then
develop into gustatory receptor cells.
Basal Cells
Taste buds are found in elevations on the
tongue
o increase the surface area and provide a
rough texture to the upper surface of the
tongue
Papillae
o About 12 very large, circular vallate
papillae or circumvallate papillae form an
inverted V-shaped row at the back of the tongue. Each of these papillae houses 100–
300 taste buds.
Vallate Papillae (wall like)
o are mushroom shaped elevations scattered
over the entire surface of the tongue that
contain about five taste buds each.
Fungiform Papillae (mushroom like)
o located in small trenches on the lateral
margins of the tongue, but most of their
taste buds degenerate in early childhood.
Foliate Papillae (Leaflike)
threadlike structures contain tactile
receptors but no taste buds. They increase
friction between the tongue and food,
making it easier for the tongue to move food
in the oral cavity
Filiform Papillae (threadlike)
o Chemicals that stimulate gustatory receptor
cells
o Once a tastant is dissolved in saliva, it can
make contact with the plasma membranes
of the gustatory microvilli, which are the
sites of taste transduction.
Tastants
The threshold for taste varies for each of the primary
tastes. The threshold for bitter substances, such as
quinine, is lowest.
Because poisonous substances often are bitter,
o the low threshold (or high sensitivity) may
have a protective function
The threshold for sour substances (such as lemon),
as measured by using hydrochloric acid, is
somewhat higher.
The thresholds for salty substances (represented
by sodium chloride)
For sweet substances (as measured by using
sucrose) are similar, and are higher than those for
bitter or sour substances
Complete adaptation to a specific taste can occur in
1–5 minutes of continuous stimulation.
Taste adaptation is due to changes that occur in the
taste receptors, in olfactory receptors, and in
neurons of the gustatory pathway in the CNS.
TASTE THRESHOLDS AND ADAPTATION
serves taste buds in the anterior two-thirds
of the tongue
Facial (VII) Nernve
serves taste buds in the posterior one-third
of the tongue
Glossopharyngeal (IX) Nerve
serves taste buds in the throat and
epiglottis
Vagus (X) Nerve
o From the taste buds, nerve impulses
propagate along these cranial nerves to the __________ in the medulla
oblongata
Gustatory Nucleus
From the medulla, some axons carrying taste signals
project to the l_______ and the
__________; others project to the thalamus.
Taste signals that project from the thalamus to the
primary gustatory area in the insula of the cerebral
cortex
limbic system, hypothalamus
