6. Gustation

Question 1

what are the two major roles of gustation?

Answer 1

• evaluating the nutritional content of food
• preventing the ingestion of toxic compounds

Question 2

taste buds sit on top of:

Answer 2

papillae

Question 3

how many different types of papillae are there?

Answer 3

four

Question 4

type of papillae with large bumps and taste buds

Answer 4

fungiform papillae

Question 5

type of papillae that are dome shaped, have taste buds, and forms a V at the back of the tongue

Answer 5

circumvallate papillae

Question 6

type of papillae found at the base of the tongue (anterior to the circumvallate papillae) and has taste buds

Answer 6

foliate papillae

Question 7

type of papillae that has small bumps but no taste buds

Answer 7

filiform papillae

Question 8

flavour associated with foods rich in glutamates including monosodium glutamate (MSG)

Answer 8

umami

Question 9

how many cells can be found on a taste bud?

Answer 9

50-150 cells

Question 10

how often do taste cell receptors turn over?

Answer 10

5-10 days

Question 11

how many types of taste cell receptors are there?

Answer 11

4
- types I, II, and III are taste receptors
- type IV basal cells become new taste receptors

Question 12

what type of cells detect salty taste?

Answer 12

type I cells

Question 13

what type of cells detect sour taste?

Answer 13

type III cells

Question 14

what type of cells detect different variants for sweet, umami, and bitter

Answer 14

type II cells

Question 15

what type of taste receptors don’t have any afferents?

Answer 15

type I receptors

Question 16

how much salt is needed for food to taste salty?

Answer 16

50mM (saliva normally has 10mM salt)

Question 17

when the concentration of Na+ in the mouth increases, it passes through:

Answer 17

permeable Na+ channels (not voltage-gated)

Question 18

list the three steps in the theorized mechanism of type I cell activation

Answer 18

1) Na+ from salt food enters through a Na+ channel
2) the resulting depolarization opens voltage-gated Ca++ channels
3) the influx of Ca++ causes neurotransmitter release

Question 19

what are the issues with the theorized mechanism of type I cell activation?

Answer 19

• no identified neurotransmitters
• not associated with afferent fibers

Question 20

what taste is associated with type III cells?

Answer 20

sour taste

Question 21

what type of receptors are type III cell receptors?

Answer 21

ionotropic

Question 22

what molecule is detected by type III cell receptors?

Answer 22

detects hydrogen ions (H+) –> detects acid

Question 23

involves a transient receptor potential channel (TRPP3) conjoined with a polycystic kidney disease family protein (PKD1L3)

Answer 23

type III cells

Question 24

is the passage of ions through TRPP3 channels enough to depolarize the type III taste cells?

Answer 24

no (weak acids also pass through the lipid membrane)

Question 25

how do H+ ions affect K+ channels in type III cells?

Answer 25

H+ ions close the K+ channels and cell depolarizes

Question 26

what happens to type III cells when K+ channels close?

Answer 26

voltage-gated Na+ channels open --> action potentials --> voltage gated Ca++ open

Question 27

what neurotransmitter is released from type III cells?

Answer 27

serotonin (5HT)

Question 28

what taste is associated with type II cells?

Answer 28

sweet, umami, and bitter

Question 29

what type of receptors are found on type II taste cells?

Answer 29

metabotropic receptors

Question 30

a heterodimer of the two taste receptor proteins, T1R2 and T1R3, is responsive to:

Answer 30

sweet tastes (sugars)

Question 31

a heterodimer of the two taste receptor proteins, T1R1 and T1R3, is responsive to:

Answer 31

L-glutamate and other L-amino acids (umami taste)

Question 32

a homodimer of the two taste receptor proteins from the TR2 family is responsive to:

Answer 32

bitter tastes

Question 33

type II cell receptors are _____ coupled, and lead to the opening of _____

Answer 33

Gq, TRPM5 channels

Question 34

what happens when TRPM5 channels open?

Answer 34

an Na+ influx depolarizes the cell and action potentials are generated

Question 35

in type II cells, the second messenger Ca++ opens ____ in addition to TRPM5 channels

Answer 35

Panx1 channels

Question 36

what is the purpose of Panx1 channels?

Answer 36

releases ATP into the extracellular space --> acts as a neurotransmitter

Question 37

ATP can bind to _____ on type II and type III cells and _____ on afferents

Answer 37

P2Y receptors (metabotropic), P2X receptors (ionotropic)

Question 38

the opening of P2X channels allows for:

Answer 38

influx of cations (Na+ and Ca++)

Question 39

are there any 'spicy' taste receptors?

Answer 39

no

Question 40

where do 'spicy' chemicals bind?

Answer 40

free nerve endings = thermoreceptors in the tongue, mouth, and airway

Question 41

have 6 transmembrane units and are found in many sensory systems

Answer 41

TRP channels

Question 42

TRP channels activated by 'warm' sensations, capsacin, and spicy foods

Answer 42

TRPV1 channels

Question 43

TRP channels activated by 'cool' sensations, and menthol

Answer 43

TRPM8 channels

Question 44

TRP channels activated by very cool temperatures and wasabi

Answer 44

TRPA1 (Anktm1)

Question 45

channels often co-expressed on sensory nerve fibers

Answer 45

TRPA1 and TRPV1

Question 46

which three cranial nerves convey taste from the tongue to the brainstem?

Answer 46

- facial nerve (fungiform papillae on the anterior 2/3 of the tongue) - glossopharangeal nerve (circumvallate and folitate papillae on the posterior 1/3 of the tongue) - vagus nerve (associated with free nerve endings)

Question 47

the afferents of CN VII, IX, and X project to the _____ in the brainstem, which projects to the _____ of the thalamus, which projects to the _____

Answer 47

nucleus tractus solitarus (nTS), ventral posterior medial nucleus (VPM), insular cortex

Question 48

- involved in perception arising from interoceptors - contains the gustatory cortex - activated during disgust and pain - reciprocal connections with secondary somatosensory cortex and amygdala - associated with orbitofrontal cortex and lateral hypothalamus these are all characteristics of the:

Answer 48

insular cortex