Gustation

Question 1

Do taste cells have neurons which project to higher brain regions?

Answer 1

Sort of: don’t have their own nerves, but are connected to cranial nerve terminals

Question 2

Describe the volatility of gustatory compounds. How does this different from olfactory compounds?

Answer 2

Non volatile, as opposed to olfactory molecules, which are volatile

Question 3

How many circumvallate papillae are there?

Answer 3

3-13

Question 4

How many taste buds are contained in the circumvallate papillae?

Answer 4

252 taste buds per papillae

Question 5

How many foliate papillae are there?

Answer 5

10-12

Question 6

How many taste buds are there contained in a foliate papilla?

Answer 6

117

Question 7

How many fungiform papillae are there?

Answer 7

200

Question 8

How many taste buds are there in a fungiform papilla?

Answer 8

1-18

Question 9

Which cranial nerve terminates in the circumvallae and foliate papillae?

Answer 9

Glossopharyngeal (IX)

Question 10

Which cranial nerve terminates in the fungiform papillae?

Answer 10

Chorda tympani (VII)

Question 11

Which other sensory systems contribute input to gustation? (2)

Answer 11

Visual system
Olfactory system

Question 12

True or False: The modified epithelial cells of the taste buds generate APs

Answer 12

True

Question 13

What kind of tissue are taste receptor cells?

Answer 13

Epithelial

Question 14

Taste receptor cells are replaced this often

Answer 14

Every 2 weeks

Question 15

Which taste modalities use GPCRs?

Answer 15

Bitter, sweet, and umami

Question 16

Describe the 2 possible taste receptors for sweet

Answer 16

Can be homo or heterodimer of T1R2 and T1R3

Question 17

Why don’t cats have a sweet taste?

Answer 17

Because they have a knock out in the T1R2 receptor gene

Question 18

Describe the receptor for umami

Answer 18

Heterodimer of T1R1 and T1R3

Question 19

What is the specific taste of umami detecting?

Answer 19

L-amino acids: aspartate and glutamate

Question 20

What is common between the sweet and umami taste receptors?

Answer 20

T1R3

Question 21

What is the name of the receptor family of bitter taste receptors?

Answer 21

T2Rs

Question 22

How many genes make up the T2R (bitter) receptor family?

Answer 22

30

Question 23

Why might there be more T2Rs in mice than in humans?

Answer 23

Humans are more visual: might need to rely on taste less

Question 24

Describe human TRP channels (4)

Answer 24

6TM domains
Nonselective cation channels
Many thermosensitive (capsaicin/menthol)
Many associated with GPCRs

Question 25

When PLC is knocked out, which taste modalities are also knocked out?

Answer 25

Umami, sweet, and bitter

Question 26

When TRMP5 channels are knocked out, which taste modalities are knocked out?

Answer 26

Umami, sweet, bitter

Question 27

Are bitter receptors expressed alone, or coexpressed with other bitter receptors?

Answer 27

Coexpressed: just need cells to respond to initiate aversive reaction

Question 28

What does it mean for a cell to be "broadly tuned"

Answer 28

It is able to respond to a wide variety of ligands

Question 29

Are sweet and umami receptors coexpressed with bitter receptors?

Answer 29

No

Question 30

What is PKD2L1?

Answer 30

Polycystronic kidney disease channel: a TRP-like channel which was thought to be the sour channel but is NOT!

Question 31

What is the channel which mediates sour taste?

Answer 31

OTOP1

Question 32

What is OTOP1?

Answer 32

A H+-gated ion channel, entry of H+ into the cell causes depolarization

Question 33

What are 2 possible modes of tasting carbonation?

Answer 33

1. Activates mechanoreceptors in taste cells 2. Carbon dioxide of sparkling water interacts with water to make bicarbonate, releases H+ and activates OTOP1

Question 34

What is the sodium taste receptor? (Name of receptor)

Answer 34

ENaC

Question 35

Describe ENaC

Answer 35

Epithelial sodium channel: not very well understood -- unknown mechanism

Question 36

ENaC is a (1)-sensitive ion channel

Answer 36

Amiloride

Question 37

ENaC allows the passage of (1) ions

Answer 37

Na+

Question 38

What are the 3 families of chemosensors in drosophila

Answer 38

Odorant receptors Ionotropic receptors Gustatory receptors

Question 39

Olfactory receptors in drosophila are present on this body part

Answer 39

Antennae

Question 40

Flies injest their food through this structure

Answer 40

Probiscis

Question 41

Where are the 3 locations drosophila have gustatory receptors?

Answer 41

Wings Legs Mouthparts

Question 42

Describe the labelled line model

Answer 42

Within a taste bud, different cells respond to a different taste modality

Question 43

Describe the across-fiber model

Answer 43

Every cell has taste receptors for different taste modalities

Question 44

Given that the GPCR taste modalities all use PLC and TRPM5, how is this evidence for the labelled line model?

Answer 44

Evidence because if they were in the same cell we would not be able to discriminate between bitter/sweet/umami

Question 45

What are the 2 pieces of evidence in support of the labelled line hypothesis

Answer 45

1. Some pathways use the same downstream cascade but we can discriminate between them 2. Sour receptors are found in different cells than sweet/umami/bitter

Question 46

Are sweet and umami expressed in the same cells?

Answer 46

No

Question 47

Why are TRCs arranged in that ball-like shape?

Answer 47

Not confirmed: but possible that this is for lateral inhibition

Question 48

Are human taste preferences innate?

Answer 48

Yes, but they can be affected by learning and memory

Question 49

How did they test the question that sweet perception was due to the receptors or the cell? What receptor was used? What was the result?

Answer 49

Express an exogenous, unrelated receptor in a sweet-responsive cell and see if the ligand for that receptor can activate sweet perception Receptor: RASSL, ligand: spiradoline Preference for spiradoline water: seems to mediate sweet response! Therefore the cell is dependent on the response: even more evidence for the labelled line theory! Did the same for bitter cells and found spiradoline mediated avoidance