lecture 13 & 14 (test 2) Flashcards
_____ is necessary for survival
eating
being attuned to taste allows us to ______
avoid toxins
taste signals are produced in the
oral cavity
taste buds are on the ______
tongue
roof of mouth
back of mouth
where are taste buds found
in grooves called papillae
how many taste buds are per cilia
6
fungiform papillae
named after the mushroom
tip of tongue
cranial nerve VII
foliated papillae
middle of the tongue
circumvallate papillae
back of tongue
cranial nerve IX
how do tastants reach taste buds
saliva borne foods flow into taste pores that lead to taste buds
taste buds contain _____ and ______ taste receptors
light and dark
light cells
make synapses onto gustatory afferent
dark cells
glia like function… support
how many specialized receptor cells within each taste bud
50-150
tastants enter receptor cells though
microvilli
what is the purpose of the microvilli
increase the surface area so more tastants can bind
3 types of taste receptors
type I
type II
type III
type I taste receptors
- glia like function
- do NOT have synapses with gustatory afferent
- most common (50%)
type II taste receptors
- respond to sweet, bitter, umami
- do NOT have synapses with gustatory afferent
- Release ATP in a non-vesicular way which acts on adjacent cells or nerve fibers that indirectly affect the activity of gustatory afferent and neighboring type III cells
- 30%
type III taste receptors
- respond to sour and salty taste
- synapse with gustatory afferent
- 20%
taste transduction for salty and sour
ion channel
taste transduction for bitter, sweet and umami
GPCR
tastant for salty transduction
Na+ ions
tastant for sour or acidic
H+ ions
types of G protein-coupled tastant receptors
(type 1 taste receptor) T1Rs and T2Rs
type 2 taste receptors (T2Rs)
- bitter taste receptor
- may function as monomer or dimer
- ligands: chemicals, especially those in the nitrogen-containing alkaloids
type 1 taste receptors (T1Rs)
- function as heterodimers, need T1R3s
- sweet: T1R2-T1R3
- umami: T1R1-T1R3
- sweet ligands: sugars
- umami ligands: amino acids
Steps to taste transduction
- GPCR activated
- depolarization directly or indirectly
- voltage-gated Na+ and K+ channels are activated and voltage-gated Ca2+ channels open
- Ca2+ causes serotonin release into the synaptic cleft
afferent taste neurons are _______
pseudounipolar
taste info is carried by which cranial nerves that emerge from the brainstem
VII, IX, X
neural coding
the way the values of tastants are represented in a pattern of APs relayed to the bring from taste buds
labeled line coding
different receptors and their associated sensory fibers are responsible for transmitting highly specific information
cross fibre coding
different qualities of a sensory modality are distinguished by the pattern of nerve discharges across a large population of fibres
tongue map urban legend
believed that each taste is detected only on particular places on the tongue
tongue map redefined
receptors for all four basic tastes are distributed over the entire tongu
regional coding
- all tastes can be detected over the entire tongue surface
chemotropic organization
different regions of the tongue have slightly different thresholds for various tasted
real world taste intensities are produces by …
the summation across fibers varying thresholds
sweetness is an activity of ___
all tastes combined
support of combinatorial model
- some taste receptors cells are selectively sensitive to particular tastants, others are broadly tune
generalist
taste receptor cell that responds secondarily to other taste stimuli via cell to cell communication within the taste bud
combinatorial taste coding model
there is convergence of receptor cell inout onto afferent axon
afferent axons are less selective
gustatory processing in the brain
1) taste signals transmitted via cranial nerves to
2) nucleus of the solitary tract, a collection neurons in the medulla
3) nucleus of the solitary tract axons project to a nucleus in the thalamus to
4) primary gustatory cortex (in frontal lobe within the sylvian fissure), insula and surrounding areas
how does taste project
ipsilaterally
flavour=
taste + smell
orbitofrontal cortex
- processes higher aspects of taste function (motivational effects of hunger and satiety)
- some neurons are multimodal
secondary gustatory cortex and beyond pathway
1) taste receptors
2) brain stem
3) thalamus
4) primary taste cortex
5) secondary taste cortex (hypothalamus, amygdala)
amygdala in secondary taste cortex
emotional connection
what the food looks like impacts the experience of eating food
hypothalamus in secondary taste cortex
motivation and memory which connects to amygdala and emotion
2 perceptual aspects of taste
intensity
quality of taste
electrogustometry
- small electric current though electrode of metal disk delivered to a specific spot on the tongue or in the oral cavity
- applied in a highly discrete manner
- can ONLY stimulate sour and salty
- can measure taste detection threshold
- useful for locating lesions
- well-controlled
deliver ions to taste buds
chemogustometry
- regional, not easily discrete, take cue tip with solution and place on areas of the tongue
- whole mouth: how long will they swish, and hold in the mouth, drink 8 cups of solution 4 sweetened, 4 distilled, they sort which ones are which, tells threshold where they cant sort as sweet
apply a chemical to tongue
taste detection thresholds ost to least sensitive
bitter
sour
salty
sweet
for survival most sensitive to detect things that may be poison
thresholds are affected by …
- making (other tastants in the mixture)
- temperature
- location on tongue
- age
- stimulation area (greater area stimulated stimulates more receptors at the same time … decreasing the threshold)
ageusia
- total loss of taste
- injury to gustatory nerves
- maybe from medications
hypogeusia
- reduction in taste sensitivity
- dry mouth, cant dissolve tastants as well
- smoking can also damage taste receptor cells
dysgeusia
- taste perceptions are distorted
- i.e. metallic taste for cancer patients, the chemical in chemotherapy end up getting secreted in saliva
4 basic tastes
sour
salty
bitter
sweet
basic tastes are defined as
hardwired effects
born liking or disliking
some believe umami should count but not universally like or dislike
taste provides information
each taste responsible for a certain nutrient salty=ion transport sweet=energy sour=damage to body bitter= poisonous
taste for pleasure (affect)
reflexive innate responses babies responses... sweet=smil spour=pucker suggested innate because babies haven't developed an outer layer of brain and still show these responses
Specific hunger theory
- we crave nutrients that we are missing
- innate cravings for sweet and salty do more harm than good
- experiments showing babies and rats preferring varied diets but to make them not feel sick and because they prefer a variety
how do we learn to like or dislike food
the consequences of eating them
lead to conditional taste preferences and aversion
innate preferences+learnes olfactory effect= likes and dislikes
adaptation
prior or ongoing stimulation reduces the perceived intensity of a tastant
the time required depends on tastant concentration
normally doesn’t occur because of food not being in the mouth long enough
cross-adaptation
perceived intensity of a compound decreases because of adaptation to a different compound
i.e. lemonade tastes sourer after eating dessert
4 taste qualities don’t dross adapt
PTC and PROP
when dissolved in water taste bitter to people who have 1-2 dominant alleles of the TAS2R38 gene
tasters are more finicky eaters
fewer tasters are alcoholics and smokers
supertaster
- an individual with taste sensations that are more intense
- impacted by genetics and fungiform papillae concentration
- people vary 5-60 papillae per 6mm diameter
- experience most intense sensation of oral burn
health consequences of taste sensations
- some bitter food are actually good for us (scientists think AMP molecule may alter bitterness)
bitterness sensitivity in women
increased sensitivity to protect the fetus during pregnancy
sensitivity diminishes after menopause
artificial sweeteners
sweet taste with essentially no calories
seniors loss in appetite
taste receptors are lost with age
supertasters are more likely to get colon cancer why…
they eat fewer vegetables because of the intense bitterness
