Gustation Flashcards
What are the 2 roles for gustation?
- evaluating the nutritional content of food
- preventing the ingestion of toxic compounds
Where are taste buds located on the tongue?
on top of papillae
What are the 4 different types of papillae? Which ones have taste buds?
- fungiform (taste buds)
- circumvillate (taste buds)
- foliate (taste buds)
- filiform (NO taste buds)
Describe the shape/size of fungiform papillae. Do they have taste buds on them? Where are they located on the tongue?
- large bumps
- taste buds
- located at tip of tongue
Describe the shape/size of circumvillate papillae. Do they have taste buds on them? Where are they located on the tongue?
- dome-shaped bumps
- taste buds
- forms a V at back of tongue
Do foliate papillae have taste buds on them? Where are they located on the tongue?
- taste buds
- located at base of tongue
Describe the shape/size of filiform papillae. Do they have taste buds on them?
- small bumps
- no taste buds
TRUE or FALSE: the distribution map for different tastes is all the same because each taste bud can have all different taste receptors
TRUE
What are the tastes that we can detect?
- bitter
- salty
- sweet
- umami
- sour
What kinds of food are considered umami?
foods rich with glutamates like MSG
How many cells does each taste bud have?
50-150 cells of 4 types
How often is the taste bud receptor turnover?
5-10 days
Which types of taste bud cells are taste receptors? basal cells?
- I, II, III = taste receptors
- IV = basal (develop into new taste receptors)
How many types of taste bud cells are there?
4 (I-IV)
According to the slides, which type of taste receptor cell is responsible for salty taste? sour taste? sweet taste? umami taste? bitter taste? water?
- salty = type I
- sour + water= type III
- sweet + umami + bitter = type II
According to the notes, what is the mechanism for type I cells?
- Na+ from salty food enters through a Na+ channel
- resulting depolarization opens V-gated Ca2+ channels
- influx of Ca2+ causes NT release
Provide an example that demonstrates how insensitive type I cells are.
saliva is normally 10 mM NaCl, but for food to taste salty, need >50 mM NaCl
What is the mechanism for type III cells?
- protons pass through a TRPP3 channel conjoined with a polycystic kidney disease family protein (PKD1L3)
- weak acids also pass through lipid membrane
- H+ ions close K+ channels –> cell depolarization
- open V-gated Na+ channels –> AP
- V-gated Ca2+ channels open
- 5HT released
What is the general mechanism for type II cells?
- GPCR senses sweet/umami/bitter
- GDP –> GTP-alpha
- PLC cleaves PIP2 to IP3
- IP3 binds to Ca2+ channel; Ca2+ influx
- TRPM5 channel opens
- Na++ influx depolarizes the cell
- APs generated
Which taste receptor proteins make up the sweet type II receptor? Describe the structure. What do they detect?
- heterodimer of T1R2 and T1R3
- sugars: glucose, fructose, sucrose, aspartame
Which taste receptor proteins make up the umami type II receptor? Describe the structure. What do they detect?
- heterodimer of T1R1 and T1R3
- detect L-glutamate and other L-amino acids
Which taste receptor proteins make up the bitter type II receptor? Describe the structure. What do they detect?
-dimers of 2 taste receptor proteins from the T2R family
How is ATP released when we detect sweet, umami, and bitter?
- Ca2+ that flows in from the type II receptor GPCR not only opens TRPM5 channels, but it also…
- opens Panx1 channels, releasing ATP into the extracellular space
TRUE or FALSE: type I and II taste receptors are ionotropic, whereas type III is metabotropic
FALSE: type I and III = ionotropic; type II = metabotropic
Explain how type II and type III afferents influence each other.
- ATP released by type II can bind to P2Y receptors (metabotropic) on type II and III cells and P2X receptors (ionotropic) on afferents
- P2X opening allows influx of Na+ and Ca2+
TRUE or FALSE: there are no bitter taste receptors
FALSE: there are no spicy taste receptors
Where do spicy stimuli bind? What kind of receptors are these?
- bind to free nerve endings
- thermoreceptors in the tongue, mouth, airway
What kind of channels are found on thermoreceptors?
TRP channels in free nerve endings in the tongue and mouth
What are TRP channels sensitive to?
temperature
How many transmembrane units make up TRP channels?
6
What temperature range do warm fibers detect? cold fibers? What is the main TRP channel associated with these fibers?
- warm fibers = above 25 degrees C, TRPV1
- cold fibers = below 25 degrees C, TRPM8; below 17 degrees C, TRPA1
WHat activates TRPV1?
capsaicin
What acitvates TRPM8?
menthol
What activates TRPA1?
wasabi and cinnamon
What behaviours does activation of TRPA1 elicit?
tears, airway resistance, cough
Explain why wasabi gives a hot sensation even though it activates TRPA1 (which is associated with cold fibers).
TRPA1 is often co-expressed with TRPV1 (associated with hot fibers)
Which cranial nerves convey taste from the tongue to the brainstem? Which parts of the tongue does each nerve innervate?
- facial VII: anterior 2/3 of tongue
- glossopharyngeal IX: posterior 1/3 of tongue
- vagus X: free nerve endings (spicy)
To which nucleus in the brainstem do the cranial nerves in the tongue travel? Where does it travel from here?
NTS –> VPM of thalamus –> insular cortex –> primary gustatory cortex
Which area of the cortex is involved in perception arising from interoceptors (e.g. full bladder, stomach upset)?
insular cortex
In which area of the cortex is th gustatory cortex found?
insular cortex
When is the insula activated?
during pain and disgust
Where does the insula have reciprocal communications?
- secondary somatosensory cortex (S2)
- amygdala
(hint: food is emotional)
Which part of the cortex is associated with value and reward in terms of gustation?
orbitorfrontal cortex
Which part of the brain is associated with regulating food intake?
lateral hypothalamus
TRUE or FALSE: olfactory and gustatory integration occurs in the hypothalamus
FALSE: in the insular cortex
