Physiology: taste

Question 1

SPACED
What is the signal?
What is the peripheral receptor?

Answer 1

Tastants
Taste cells

Question 2

SIGNAL
What substance helps the tastants get to taste cell?

Answer 2

Saliva

Question 3

SIGNAL
- How does saliva help tastants get to the taste cells?
- What part of the taste cells will tastants ultimately bind to?

Answer 3

Solubilisation of tastants: tastants can interact with receptors
Diffusion of tastats: spreads tastants over the tongue

Receptor proteins on their apical surface/microvilli

Question 4

PERIPHERAL RECEPTORS
Name the subcomponents of the tongue

Answer 4

Tongue –> papillae –> taste buds –> taste cells

Question 5

PERIPHERAL RECEPTORS: PAPILLAE
Differentiate filiform and fungiform papillae
Memory trick?

Answer 5

Fungiform are larger, like mushrooms (fungi)
Filiform fill in the rest of the space

Question 6

PERIPHERAL RECEPTORS: PAPILLAE
Differentiate circumvallate (vallate) and folate papillae

Answer 6

Question 7

PERIPHERAL RECEPTORS: TASTE BUDS
- How many taste cells per taste bud?
- Taste cells need to be frequently replaced, as they’re epithelial and exposed to toxins. How is this done?

Answer 7

50-150
Taste buds have a basal cell population (stem cells - replace them)

Question 8

PERIPHERAL RECEPTORS: TASTE CELLS
What cell type is it?

Taste cells have an apical and basal pole.

At the apical pole:
- How does it reach the surface of the tongue?
- What cytoskeletal structure does the apical pole have?
- What signal transduction molecules are found on these cytoskeletal structures?

At the basal pole:
- What does it communicate with?

What is the main signalling molecule and NT? Secondary?

How many major classes of taste cells are there?

Answer 8

Epithelial

It goes through an opening in the taste bud called the taste pore
Microvilli, receptor proteins

Afferent neurons (via synapses)

ATP, serotonin

3

Question 9

PERIPHERAL RECEPTORS: TASTE CELLS
Type I glial like cells
- What taste type do they detect?
- What receptor type (for tastants) do they have?

Answer 9

Salty
Na+ channel

Question 10

PERIPHERAL RECEPTORS: TASTE CELLS
Type II receptor cells
- What taste types do they detect?
- What receptor type (for tastants) do they have?
- What other major membrane channels does it have? What is its role?

Answer 10

Bitter, umami, sweet
GPCR’s (different combinations for the above tastes)
Panexxins: form membrane channels that allow ATP to be secreted into the extracellular space

Question 11

PERIPHERAL RECEPTORS: TASTE CELLS
Type III presynaptic cells
- What taste does it detect?
- What receptor type does it have?

Answer 11

Sour
Ion channel (Na+ and H+ influx)

Question 12

PERIPHERAL RECEPTORS: TASTE CELLS
Type III presynaptic cells
- What 2 signals can they depolarise in response to?

Answer 12

Sour tastants themselves
ATP released by type II cells binding to P2Y receptors

Question 13

PERIPHERAL RECEPTORS: TASTE CELLS
Type III presynaptic cells
- What is the main NT it releases?
- What other NTs does it release?

Answer 13

Serotonin
NPY and CCK (satiety signals), ATP

Question 14

PERIPHERAL RECEPTORS: TASTE CELLS
Signal transduction
- Describe signal transduction in type II cells

Answer 14

Question 15

PERIPHERAL RECEPTORS: TASTE CELLS
Signal transduction
- Describe signal transduction in type III cells

Answer 15

Binding of sour tastant

Depolarisation leads to intracellular calcium release/AP generation –> exocytosis of 5-HT (serotonin) –> stimulation of afferent sensory neuron

Question 16

AFFERENT PATHWAYS
How many order neurons are there?

Answer 16

3

Question 17

AFFERENT PATHWAYS
First order neurons
- Where are their dendrites located?
- What cranial nerves form their axons
- Where do they synapse?

Answer 17

Superior tongue, inferior tongue, pharynx
Cranial nerve 7 (facial), 9 (glossopharyngeal), 10 (vagus)
NTS of the medulla

Question 18

AFFERENT PATHWAYS
Second order neurons
- Where are their somas located?
- Where do they project to?

Answer 18

Somas in the NTS of the medulla

Project to the ventral posterior medial nucleus of the thalamus

Question 19

AFFERENT PATHWAYS + CENTRAL PROCESSING
Third order neurons
- Where are their somas located?
- Where do they project to? (This is also their site of central processing)

Answer 19

Soma in the ventral posterior medial nucleus of the thalamus

Project to the gustatory cortex (anterior insula)

Question 20

AFFERENT PATHWAYS + CENTRAL PROCESSING
Label the following

Answer 20

Question 21

DISRUPTION
Names for:
- Inability to taste?
- Decreased taste?
- Distorted taste?

Can taste disruption have a strong impact on QoL (eg. depression and anxiety)?

Can disrupted taste be life threatening?

Answer 21

Ageusia, hypogeusia, dysgeusia
Yes
Yes - esp if can’t detect toxic tastes