5b. Taste

Question 1

Number of Tastebuds

Answer 1

10,000 in humans
1,700 in dogs
500 in cats

Question 2

3 Types of Papillae

Answer 2

• Circumvallate (caudal)
• Foliate (middle)
• Fungiform (rostral)

Question 3

Tate buds

- 3 Cell Types

Answer 3

Taste Receptors

Supporting cells

Basal cells

Question 4

Taste Receptors

- 2 Types

Answer 4

• Receptor cells, which don’t form synapses with afferents

- Presynaptic cells, which form synapses with afferents

Question 5

Taste Receptor Cells

- Length

Answer 5

Short

Question 6

Complex Taste Modalities that Require a G-Protein Coupled Receptor

Answer 6

• Bitter
• Sweet
• Umami

Question 7

Simple Taste Modalities that Directly Alter Ion Flux

Answer 7

• Salty

- Sour

Question 8

G-Protein Coupled Receptor Cascade

- Initiation and Intracellular events

Answer 8

βy subunit activate PLCβ which hydrolyses PIP2 into DAG and IP3

Question 9

G-Protein Coupled Receptor Cascade

- 3 Ca2+ effects

Answer 9

1. Opens TRP5M cation channels allows Na+ influx and depolarisation
2. Opens Panx1 heavy channels which allow ATP efflux which acts as a purinergic transmitter to carry the signal to afferent fibres and presynaptic cells.
   Panx1 is a gap junction hemichannels
3. Transmitter release from receptor cells via gap junction hemichannels

Question 10

Bitter Receptors

Answer 10

30 T2R receptors

May dimerise

Question 11

Sweet Receptors

Answer 11

Rostral taste buds

Heterodimers:

• T1R2
• T1R3

Question 12

Umami Receptors

Answer 12

Heterodimers:

• T1R1
• T1R3

Question 13

Sour

Answer 13

Registered by all taste buds

Weak undissociated acid diffuses into presynaptic cell and dissociates

Intracellular H+ blocks K+ channels leading to depolarisation, Ca2+ release and vesicular transmitter release

Question 14

Salt

Answer 14

Rostral taste buds

Na+ entry into glia-like cells through epithelial Na+ leak channels, causing depolarisation Ca2+ release and vesicular transmitter release

Question 15

Afferent Fibres

- Fibre Types

Answer 15

Afferents from tongue project in:

• Chordates tympani of cranial nerve VII (fascial)
• Cranial nerve IX (glossopharyngeal)

Afferents from threat project in:
- Superior laryngeal nerve of cranial nerve X (vagus)

Question 16

Higher Taste Pathway

- Primates

Answer 16

1. Solitary nuclear complex of the medulla within the gustatory nucleus
2. Ventral posterior medial nucleus of the thalamus
3. Primary gustatory cortex in the anterior insula and frontal operculum

• Orbitofrontal cortex (palatability)
• Amygdala (motivational drives)
• Lateral hypothalamus (feeding behaviour)

Question 17

Higher Taste Pathway

- Sub-Primate Species

Answer 17

Thalamocortical pathway runs via a pontine relay in the parabranchial nucleus, where changing physiological conditions may modify feeding behaviour

Question 18

Taste Coding

Answer 18

Across fibre code