Flashcards in Lecture 2 - Gustatory System Deck (80):
What are tastants?
Nonvolatile molecules that are soluble in saliva and activate taste receptors
What are the 5 taste modalities and what chemical they taste?
1. Salty: Na+
2. Sour: H+
3. Sweet: sugars
4. Umami: glutamate and other AAs
5. Bitter: many chemicals
Describe the threshold of taste modalities? Explain
High except for bitter because a lot of bitter chemicals are toxic so should be avoided
Does taste equal flavor?
Flavor = taste + smell
What are tastants detected by? Where?
Taste receptors on the tongue, pharynx, epiglottis, upper part of esophagus
Which part of the mouth has the highest concentration of taste receptors?
In what type of cells are taste receptors located? 2 names
Taste receptor cells (TRCs) = taste bud cells (TBCs)
What is a taste bud? Where is it located?
Combination of many TRCs on certain papillae
Describe the order from taste receptor to tongue
Taste Receptor ►Taste Receptor Cells ►Taste Bud ►Papillae ► Tongue
What are papillae?
Lingual epithelium protrusions
What are the 4 types of papillae? Which ones have taste buds?
1. Circumvillate papillae*
2. Foliate papillae*
3. Fungiform papillae*
4. Filiform papillae
Describe the structure of circumvillate papillae.
Connective tissue core (CT core) with taste buds in the grooves
Where does the name of circumvate papillae come from?
Form a circle and a sort of chevron (V shaped)
What % of taste buds do circumvate pupillae contain?
Where does the name of foliate papillae come from?
Grooves along the lateral aspect of the tongue actually resemble red leaf like structures
Are the foliate papillae named for the shape of their connective tissue cores?
What % of taste buds do foliate pupillae contain?
Where does the name of fungiform papillae come from?
Sort of shaped like a mushroom and protrude from surface of the tongue
Where are fungiform pupillae located?
Anterior 2/3rds of the tongue
Where is the highest density of fungiform pupillae on the tongue? Why?
Tip because first part of tongue to taste food
What % of taste buds do fungiform pupillae contain?
Which papillae with taste buds lack DEEP grooves along their sides? Therefore, where are their taste receptors?
Taste receptors on apical region
What papillae comprise the majority of papillae on the tongue?
Why are the tongues of cat so rough?
Because their filiform papillae are highly keratinized
What are the 3 basic types of TRCs? Describe the function of each.
1. Type I: glial that function in a support role
2. Type II: signal transduction
3. Type III: signal transduction
How is the cell body of type II TRCs shaped?
What type of taste receptors do Type II TRCs have? What tastants do they taste?
3 types of GPCRs:
AND 2 types of ionotropic receptors:
What type of taste receptors do Type III TRCs have? What tastants do they taste?
2 types of ionotropic receptors:
How is the cell body of type III TRCs shaped?
What kind of receptor is the TRPM5 channel?
Multisensory receptor: can sense:
How are taste receptor cells connected to each other?
What are the 2 domains of TRCs? Describe each.
1. Apical domain: exposed to tastants and where the taste receptors are
2. Basal domain
Describe the salt/sour transduction pathway.
1. Ion channels allow Na+ (Salt) or H+ (Sour) into the cell
2. Influx of Na+ or H+ causes TRC depolarization
3. Depolarization triggers voltage-gated Na+ and K+ channels in the basal domain to open
4. Further depolarization triggers voltage-gated Ca+ channels in the basal domain to open
5. Calcium mediates synaptogamin and causes NT vesicle exocytosis
Describe the sweet/bitter/umami transduction pathway.
1. GPCRs are activated by sweet, bitter, or umami tastants
2. G-protein alpha subunit activates PLC to form IP3
3. IP3 activates TRPM5 channels located in the membrane of the basal domain to let Na+ in and also releases intracellular Ca+ stores, which further activates the TRPM5 channels
4. Ion influx through TRPM5 channels causes depolarization
5. Depolarization triggers voltage-gated Ca+ channels in the basal domain to open
6. Calcium mediates synaptogamin and causes NT vesicle exocytosis
How do the ionotropic salt/sour channels work? What is each called? 2 names for first one.
Directly convey tastants through the cell membrane causing depolarization:
1. Amiloride-sensitive Na+ leaky channels (ENAC=Epithelial sodium channels)
2. H+-sensitive TRP (Transient receptor potential) channels (PDK variant)
How many subunits in sweet and umami GPCRs?
How many subunits in bitter GPCRs?
What are the 2 subunits of sweet GPCRs?
T1R2 + T1R3
What are the 2 subunits of umami GPCRs?
T1R1 + T1R3
What is the name of the G-protein used by bitter GPCRs?
What is the 1 subunit of bitter GPCRs?
What kinds of afferent signaling is performed by Type II TRCs? Describe each.
1. Synaptic release of serotonin via GPCR signaling
2. Paracrine: purinergic receptors activated by non-synaptic ATP release: P2Y (Type III TRC) and P2X (afferent fiber) => IP3 activation pathway
3. Autocrine: purinergic receptors activated by non-synaptic ATP release: P2X
What kind of afferent signaling is performed by Type III TRCs? Explain.
Synaptic signaling with serotonin release on afferent fibers
Can one Type II TRC express multiple types of GPCRs at a time?
What % of TCRs express multiple receptor types aka are sensitive to multiple taste modalities?
What are 3 factors contributing to the complexity of coding of taste signals?
1. TRCs express multiple receptor types
2. Taste buds contain multiple TRCs of varying types
3. Afferent fibers receive input from multiple TRCs (Type II and Type III) within a single taste bud and across multiple taste buds
Are taste buds across the tongue sensitive to all taste modalities?
How many taste buds on average on the tongue?
What % of humans are supertasters? What does this mean?
1. Have more than twice as many taste buds
2. Greater number of fungiform papillae on the tongue
3. Are usually more sensitive to bitter tastes due to being more likely of expressing TAS2R38 receptors to PROP (6-n-propylthiouracil)
How to determine if someone is a supertaster?
If a person has more than 30 fungiform papillae in a 1/4 inch circle
What do supertasters not like to eat? What is a consequence of this?
Fats, sugars, and strongly flavored foods/drinks (coffee, frosting, BBQ ribs, hoppy hand crafted beers)
What 2 cranial nerves have gustatory afferents? What parts do they each innervate? Where do they both synapse?
1. Facial nerve (2 branches):
- Greater petrosal: palate
- Chorda tympani: all 3 types of papillae all along the tongue
2. Glossopharyngeal nerve: circumvillate and foliate papillae at the back of the tongue
Synapse on rostral nucleus of solitary tract (rNST) in medulla
Describe the central taste pathway.
Gustatory receptors => gustatory afferents in cranial nerves => synapse at rostral nucleus of solitary tract (rNST) in medulla => synapse at ventral posteromedial nucleus (VPM) of thalamus (ipsilateral) => synapse at primary gustatory cortex => synapse at secondary gustatory cortex
What is another name for the rostral nucleus of solitary track (rNTS) in medulla?
Where is the primary gustatory cortex located?
Near hippocampus, at the anterior insula/frontal operculum
What is the function of the cNST of the medulla?
Cardiopulmonary function: breathing and heart rate
What confers emotional response to food?
rNTS also receives input from amygdala (and hypothalamus)
Where is the amygdala located?
Forebrain: medial temporal lobe
What is ageusia?
Loss of taste (for one or more tastants)
What is hypogeusia?
Loss of potentiation of taste (can't taste well)
What is dysgeusia? Cause?
Taste hallucination where foul, salty, rancid, or metallic taste sensation persists
Cause not well understood
What is dysgeusia sometimes accompanied by? Explain it.
Burning mouth syndrome = painful burning sensation in oral cavity
What are 4 causes for taste disorders (ageusia and hypogeusia)?
1. Radiation therapy for head/neck cancers
2. Head injury/surgery (eg: middle ear or wisdom teeth)
3. Poor oral hygiene/dental problems
4. Upper respiratory infections
How do we know if a chemical is a tastant?
If there is a taste receptor for it, it's a tastant
Where do the oral and nasal cavities meet?
Where are circumvillate papillae located?
Surface and V-shape in back of tongue
Where are foliate papillae located?
Lateral sides of tongue
How many folds does each foliate papillae have? What is this comparable to?
Comparable to the grooves of the circumvillate papillae
What are the 2 pathways Type III cells have to release serotonin?
1. Primary: salty/sour ionotropic receptor pathway
2. Secondary: P2YR pathway with IP3
What kind of tastant is quinine?
Is there a gustatory topography?
What % of the pop is insensitive to PROP?
How many isoforms of bitter receptor T2Rs?
Where is the secondary gustatory cortex located?
Do the cells of the secondary gustatory cortex respond to multiple tastants?
Yes, they are multimodal
What other system does secondary gustatory complex interact with?
How is the organization of the gustatory cranial nerves different from other cranial sensory systems?
2. Apparent topography
What does non-synaptic release mean?
The release does not happen at a traditional synapse as no vesicles are used
Cells bodies of the facial nerve 2 branches with afferents mediating taste are found in which ganglion?