Taste 2 Lecture 14

Question 1

What are the principle neurotransmitters for taste?

Answer 1

Serotonin and ATP

Question 2

What receptors do ATP act on?

Answer 2

P2X2 and P2X3, both are ATP gated ion channels

Question 3

What are the two theories for how taste is coded at the afferent level?

Answer 3

Labelled line model

Across fibre mode

Question 4

What does the label line model suggest?

Answer 4

That for each gustatory afferent neuron, the neuron will only detect a narrow range of tastes, 1 or 2 tastes. (very similar tastes)

i.e neurons are sensitive to a particular taste and if you lose those neurons you lose those tastes

Question 5

What does the across fibre model suggest?

Answer 5

That each gustatory afferent neuron will recognise a broad range of tastes and depolarise for them. It will have a highest rate of firing for a particular taste, but then it will also partly recognise other tastes.

Therefore if you lose that particular neuron then you will not completely lose that taste.

Question 6

Describe the coding for the labelled line model:

Answer 6

One-cell one receptor. Individually tuned nerves

Taste cell + taste receptor + Afferent neuron must be taken into account

Question 7

Describe the coding theories for the across fibre model:

Answer 7

Two theories:

One cell, many receptors, Multiple tuned (tuned to multiple tastes) nerve fibre

or

One cell, one receptor, Multiple tuned nerve fibre.

Question 8

What are the pros and cons of the labelled lined model?

Answer 8

Pros:
- Precise

Cons:
- Not many tastes possible

Question 9

What are the process and cons of the across fibre model?

Answer 9

Pros:
- Broad taste coding

Cons:
- Non-specific

Question 10

How many taste receptors (types) do taste cells have, and which theory does this support?

Answer 10

Umami and sweet receptors are never co-expresseed with bitter receptors in the same cell.

This is support for the labelled line model.

Question 11

What theory is not possible if bitter receptors can not be expressed in the same cell as sweet/umami?

Answer 11

The across fibre model where:

One cell, many receptors, Multiple tuned (tuned to multiple tastes) nerve fibre

Can not be true!

Question 12

Is taste dependent on taste cells or taste receptors?

Answer 12

Taste cells are responsible for taste not the receptor or ligand.

This gives support for the taste cells being hard wired to a particular afferent neuron and thus the labelled line hypothesis.

Question 13

If you breed mice without a specific taste receptors, what happens?

Answer 13

They lose that particular taste and not other tastes. This supports the labelled line hypothesis

Question 14

When exposing taste receptors to many tastes, what is measured in the NTS and what does this support?

Answer 14

One cell responding to many different taste qualities, but to varying degrees. One taste produces the highest firing rate

At all levels of the transduction pathways, there will be cells that respond to multiple stimuli. (integration of taste at the higher levels)

Support for the across fibre model

Question 15

Do we have some sort of integration at the level of taste buds?

Answer 15

Recording Ca transients in taste buds when stimulating them with taste stimuli.

Only one cell responded to one taste. All other cells responded to multiple tastes.

When they performed the test over all cells they found that 55% of cells respond to one taste and the 45% respond to multiple

Thus supporting the across fibre model

Question 16

Therefore which model is correct? summaries findings

Answer 16

Maybe both.

Umami, bitter, sweet narrowly tuned and exclusive to one taste (labelled line) g proteins.

Presynaptic cells broadly tuned. (contain ion channels and other receptors)

Some cells in the taste bud are specific and others a broadly tuned (across fibre modeL0

Question 17

What is aguesia

Answer 17

Aguesia (complete loss of taste)

Question 18

What is hypoguesia?

Answer 18

Diminished sense of taste (one taste)

Question 19

what is hyperguesia?

Answer 19

Enhanced sensitivity to taste (to one taste)

Question 20

What is dysgeusia?

Answer 20

Qualitative disturbance (bad taste post drugs)

Question 21

What is phantoguesia?

Answer 21

Phantom tastes in patients with schizophrenia and epilepsy

Question 22

What are the causes for taste dysfunction?

Answer 22

• Upper resp or middle ear infect
• radiation therapy for cancer
• exposure to certain chemicals
• antibiotics, antihistamines
• head injury
• ent surgery
• poor oral hygiene
• dental problems

Question 23

Describe the taste pathway:

Answer 23

Taste buds (2/3 tongue ant) Cranial nerve 7
Taste buds (post 1/3) cranial nerve 9
Taste buds (epiglottis) Cranial nerve 9

All axons go to NTS (ipsilateral)

NTS (nucleus of the solitary tract)sends fibres to VPM of thalamus and then on to the insula and frontal cortex. (contralateral projections though)

NTS sends fibres to the(ipsilateral) Hypothalamus, Amagdyla and orbitofrontal cortex. The hypothalamus also receives input from the insula and frontal cortex of the contralateral side)

Question 24

How is flavour produced?

Answer 24

Complex between taste smell and vision..

i.e blinded and nose pegged, an apple will taste the same as a potato and vice versa

Question 25

How is vision important in the analysis of taste information?

Answer 25

Give children coloured sugar water they will think that orange coloured water has orange taste.

Question 26

How does hunger affect taste?

Answer 26

Hypothalamus and orbitofrontal cortex input will influence taste and hedonic of food (appeal), so if you are really hungry then things will taste better but if you eat a lot of the same flavour, you be become full quicker than if you ate a range of flavours.

Question 27

Pleasureless of food decreases over time is known as?

Answer 27

Sensory specific satiety - long term adaptation

Question 28

What is the significance of sensory specific satiety?

Answer 28

Our taste perception can be modulated by a number of past experiences and higher complex factors integrated into taste signal