15. Gustatory - Taste

Question 1

Describe the central gustatory pathway.

Answer 1

gustatory afferents in the cranial nerves (facial + glossopharyngeal) –> gustatory nucleus, the rostral nucleus of Solitary Tract –> rNTS will relay info to the ipsilateral thalamus (AKA no decussation), the VPM nucleus –> primary gustatory cortex –> relay information to secondary gustatory cortex. The collaterals of the pathway also include amygdala and hypothalamus

Question 2

Is there gustatory topography?

Answer 2

No, taste buds all over our palate are able to respond to many different tastes.

Question 3

Type II

Answer 3

• Rounded cell body • α-gustducin positive • express only 1 of 3 types of GPCRs for Sweet, bitter, or Umami • Also express non-GPCRs for Salty + Sour • Non-synaptic paracrine communication

Question 4

Salty Receptors:

Answer 4

• salt in the oral cavity leaks into the cells through ENAC channels • depolarization of the cell opens voltage gated Ca2+ channels, and causes release of serotonin type II

Question 5

Which TBC types are capable of transduction?

Answer 5

Type II and Type III

Question 6

What are Tastants?

Answer 6

– Non-volatile, soluble/hydrophilic molecules in saliva – activate taste receptors

– In general, tastant receptors have high threshold (mM), except bitter. We have a low threshold for bitter

Question 7

Name the cranial nerves containing gustatory afferent fibers. Identify from where in the oral cavity the gustatory afferents carry information.

Answer 7

Facial nerve + Glossopharyngeal nerve Facial nerve, Gives rise to TWO branches: –> Chorda Tympani (CT) = info from fungiform + lateral foliate papillae – anterior part of tongue –> Greater Superficial Petrosal (GSP) – roof the mouth Glossopharyngeal nerve –> Info from posterior part of the tongue These two nerves synapse in the gustatory nucleus, are parts of the gustatory pathway.

Question 8

Bitter receptors:

Answer 8

• Family of T2 receptor proteins • 30+ isoforms • Single protein • Low threshold (nM)

Question 9

Fungiform Papillae

Answer 9

– their connective tissue cores look like little mushrooms. – Their taste buds are located towards the top of the structure

Question 10

5) Know the steps in transduction for the 5 taste modalities. How do the structure of bitter receptors, sweet, and umami differ?

Answer 10

Bitter, Sweet, and Umami—-These utilize GPCRs Bitter receptors: • Family of T2 receptor proteins • 30+ isoforms • Single protein • Low threshold (nM) Sweet receptor: • T1R2 + T1R3 • Protein complex • High threshold (mM) Umami receptor: • T1R1+T1R3 • Protein complex • High threshold (mM) Salty • salt in the oral cavity leaks into the cells through ENAC channels • depolarization of the cell opens voltage gated Ca2+ channels, and causes release of serotonin type II Sour Both the influx of H+ and the fact that it can cause closure of K+ leak channels which leads to depolarization of the cell since the positive is no longer leaving the cell Then get opening of voltage gated Ca2+ channels to get neurotransmitter release

Question 11

Identify factors contributing to across fiber patterning or population coding in the gustatory system.

Answer 11

– over 90% of TRCS express multiple receptor types, so — are sensitive to many taste modalities – every afferent fiber receives input from multiple TRCs within a single taste bud, and across multiple taste buds. – Usually one taste will dominate

Question 12

What are the 5 taste modalities?

Answer 12

1. Salty (salts)
2. Sour (H+)
3. Sweet (sugars)
4. Umami (glutamate)
5. Bitter (many)

Question 13

Which taste receptors utilize GPCRs?

Answer 13

Bitter, Sweet, and Umami

Question 14

Circumvalliate Papillae

Answer 14

– largest of the papillae – They have a valley that surrounds the papillae

Question 15

Type I

Answer 15

• Supporting cells • dont know if they are capable of transduction

Question 16

6) What does paracrine signaling play in the transmission of taste signaling?

Answer 16

• Paracrine signaling is important for type 2 taste receptors cells • ATP is released by type 2 in an activity dependent manner but not at the synapse, but through its own channel for paracrine signaling • TRCs can communicate with both type 3 TRCs and afferent fibers via non-synaptic ATP release, and can communicate with afferents via synaptic 5-HT release.

Question 17

Two ways that TRC’s can communicate with afferents–

Answer 17

TRC’s communicate with afferents (Type III –> Afferent fibers)

• via synaptic 5-HT release
• via non-synaptic ATP release = paracrine signaling

Question 18

Umami receptor:

Answer 18

• T1R1 + T1R3 • Protein complex • High threshold (mM)

Question 19

Paracrine and synaptic signaling from Taste Receptor Cells (TRC’s)

Answer 19

Paracrine signaling

• TRCs communicate with each other via non-synaptic ATP release (Type II –> Type III)
• TRCs communicate with afferents via non-synaptic ATP release (Type II –> Afferent fibers)

Synaptic signaling

• TRC’s communicate with afferents via synaptic 5-HT release (Type III –> Afferent fibers).

Question 20

What are the 4 types of human papillae? Which ones contain taste buds?

Answer 20

only 3 actually contain taste buds

1) Filiform Papillae
2) Foliate Papillae
3) Circumvalliate Papillae
4) Fungiform Papillae

Question 21

Type III

Answer 21

• Narrow cell body • α-gustducin negative • Salty and Sour • Gustatory presynaptic cells— form traditional synapses with afferent fibers.

Question 22

Collaterals of the Central Taste Pathway

Answer 22

NTS also projects to and receives input from:

1) Amygdala
2) Hypothalmas – hunger, satiety, Control of pituitary gland and autonomic nervous system.

Question 23

Sour Receptors

Answer 23

Both the influx of H+ and the fact that it can cause closure of K+ leak channels, leads to depolarization of the cell (since the positive is no longer leaving the cell) – opening of voltage gated Ca2+ channels to get neurotransmitter release

Question 24

Foliate Papillae

Answer 24

Foliate Papillae – taste buds are in the lateral walls of the papillae – their connective tissue cores look like leaves!

Question 25

Glossopharyngeal nerve carries afferent from –

Answer 25

Glossopharyngeal nerve –> Info from posterior part of the tongue

Question 26

human papillae are –

Answer 26

human papillae are lingual epithelium protrusions.

Question 27

Filiform Papillae

Answer 27

Filiform Papillae – composed of stratified squamous keratinized epithelium – small or non-existent connective tissue core – don’t mediate taste transduction BUT are important for texture information

Question 28

Sweet receptor:

Answer 28

• T1R2 + T1R3 • Protein complex • High threshold (mM)

Question 29

Facial nerve carries afferent info from–

Answer 29

Gives rise to TWO branches: –> Chorda Tympani (CT) = take info from fungiform papillae (anterior portion of the tongue) and lateral foliate papillae –> Greater Superficial Petrosal (GSP) – roof the mouth