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Systems Neuroscience > Taste > Flashcards

Taste Flashcards

1
Q

Other than the tongue, where else are cells that detect taste found?

A

Back of the throat.
Epiglottis.
Nasal cavity.
Upper part of the oesophagus.

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2
Q

In comparison to adults, which additional areas do children have cells that detect taste?

A

Hard palate.
Centre of the tongue.
Mucus membrane of lips and cheeks.

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3
Q

Children have more areas that contain cells that detect taste compared to adults. What does this imply?

A

We adapt and become more selective as we age.

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4
Q

What are the five basic tastes?

A

Sweet.
Sour.
Salty.
Bitter.
Umami.

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5
Q

How are orally sourced aromas processed?

A

Input through the retronasal route.
Processed by a region of the insular cortex involved in the gustatory pathway.

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6
Q

Are the basic tastes perceived equally all over the tongue?

A

Yes, except for in the centre.

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7
Q

Which two amino acids is the umami taste derived from?

A

Glutamic acid.
Aspartic acid.

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8
Q

What do papillae contain?

A

Taste buds (several hundred each).

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9
Q

What do taste buds contain?

A

Taste receptor cells.

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10
Q

How many taste buds do humans have?

A

2000-4000.

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11
Q

Where are papillae found?

A

Under the mucus membrane of the tongue.

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12
Q

What is the function of papillae?

A

To increase the surface area of the tongue to amplify the intensity of perceived taste.

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13
Q

Name the four types of papillae.

A

Filiform.
Fungiform.
Circumvallate.
Foliate.

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14
Q

Which two types of papillae are the most common?

A

Filiform and fungiform.

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15
Q

Where on the tongue are filiform and fungiform papillae found?

A

Tip and edges.

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16
Q

Which papillae contain sensory cells for touch and temperature?

A

Filiform and fungiform.

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17
Q

Which papilla is found at the base of the tongue?

A

Circumvallate.

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18
Q

How many circumvallate papilla are present on the tongue?

A

Approx. 7-12.

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19
Q

How are circumvallate papilla organised?

A

In a V-shape formation.

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20
Q

Circumvallate papillae are surrounded by a trench. What is the purpose of this?

A

Trench contains numerous glands that rinse the taste-producing substances into the taste receptor cells.

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21
Q

How many foliate papillae are present on the tongue?

A

Approx. 20.

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22
Q

How are foliate papillae arranged on the tongue?

A

Arranged in several close folds on the rear edges of the tongue.

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23
Q

How many taste receptor cells does each taste bud contain?

A

50-150.

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24
Q

How often are taste receptor cells renewed?

A

Every 10-14 days.

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25
Q

How are taste receptor cells arranged within the taste bud?

A

Form a capsule in the shape of a flower bud.

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26
Q

What is the role of the taste pore located at the tip of the capsule?

A

Works as a fluid-filled tunnel that contains microvilli (taste hairs).

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27
Q

Basal cells surround taste receptor cells at the base of the capsule. What is their role?

A

They divide to replace the taste receptor cells.

28
Q

Which axons synapse with the base of the taste receptor cells?

A

Gustatory afferent axons.

29
Q

Where are the cell bodies of the gustatory afferent axons located?

A

In the ganglia of the facial, glossopharyngeal and vagus nerves.

30
Q

Which ions are involved in producing bitter tastes?

A

Potassium.
Chloride.
Magnesium.

31
Q

How do we discriminate between similar flavours if we can only detect five basic tastes?

A

Taste receptor cells differ in their sensitivity to the different basic tastes.

32
Q

When the taste stimulus is at a concentration just above threshold, most papillae are sensitive to just one basic taste. What happens when the concentration is increased?

A

Most papillae become less selective.

33
Q

How many different gustatory transduction processes are there?

A

Three.

34
Q

What is the transduction process for salty tastes?

A

Passes directly through ion channels.

35
Q

What is the transduction process for sour tastes?

A

Binds to and blocks ion channels.

36
Q

What is the transduction process for bitter, sweet and umami tastes?

A

Binds to GPCRs in the membrane, which activates second-messenger systems that cause ion channels to open.

37
Q

What is the most chemically sensitive part of a taste receptor cell?

A

A small membrane at the apical end.

38
Q

Why is the small membrane at the apical end of the taste receptor cell the most chemically sensitive part of the cell?

A

The apical end has microvilli that project into the taste pore. The microvilli are exposed to the taste stimuli present in saliva.

39
Q

Which ion channels detect low salt concentrations in taste receptor cells?

A

Amiloride-sensitive sodium channels.

40
Q

What is an amiloride-sensitive sodium channel?

A

A sodium channel that can be blocked by amiloride (a type of diuretic).

41
Q

What happens in the taste receptor cell when you eat something salty?

A

The sodium concentration outside the cell rises higher than inside the cell.
This alters the concentration gradient across the membrane.
Sodium diffuses across the membrane into the cell.
The inward positive current causes the membrane to depolarise.
This causes sodium and calcium channels to open.
Synaptic vesicles release NT into the synapse.

42
Q

What is thought to be the primary NT of taste receptor cells?

A

ATP.

43
Q

Which NT might be released in response to salty and sour tastes (as proven in mouse studies)?

A

5-HT.

44
Q

What causes a sour taste?

A

High acidity levels.

45
Q

What happens in the taste receptor cell when you eat something sour?

A

Acids dissolve in water and generate H+ ions.
H+ ions may bind to and block specific potassium channels.
This decreases potassium permeability of the membrane, causing the cell to depolarise.
H+ ions may also activate an ion channel from the TRP (transient receptor potential) channel superfamily.
The cation current through the TRP channel depolarises the cell.
Sodium and calcium channels open.
Synaptic vesicles release ATP and maybe 5-HT into the synapse.

46
Q

Why is it believed that there may be other mechanisms of sour transduction yet to be discovered?

A

pH affects all cellular processes so there may be a complex network of processes occurring.

47
Q

The transduction mechanism for sweet, bitter and umami tastes relies on what?

A

Two related taste receptor proteins: T1R and T2R.

48
Q

How are we able to detect a vast array of different poisonous substances?

A

Bitter substances are detected by around 25 different types of T2R receptors, which are also poison detectors.

49
Q

What happens in the taste receptor cell when you eat something bitter, sweet or umami?

A

The taste molecule binds to the receptor and activates the G-proteins.
This activates phospholipase C.
This increases the production of IP3.
IP3 activates an ion channel unique to taste receptor cells.
The ion channel opens, causing an influx of sodium into the cell.
This causes depolarisation of the cell.
IP3 also triggers the release of calcium from intracellular storage sites.
Calcium activates a membrane channel, allowing ATP to flow out of the cell.
ATP activates purinergic receptors on the postsynaptic gustatory axons.

50
Q

Which specific taste receptor dimer proteins make up the GPCR that detects sweet tastes?

A

T1R2 and T1R3.

51
Q

What results in an inability to taste sweet tastes?

A

Lack of or damage to T1R2 or T1R3.

52
Q

Which specific taste receptor dimer proteins make up the GPCR that detects umami tastes?

A

T1R1 and T1R3.

53
Q

Which taste receptor dimer protein determines whether the receptor is sensitive to sweet or umami tastes?

A

T1R1.

54
Q

If the transduction mechanism is the same for bitter, sweet and umami tastes, why don’t we get confused between these tastes?

A

The receptor proteins for bitter or sweet or umami are expressed in different taste receptor cells.
The different taste receptor cells synapse onto different gustatory axons.

55
Q

The front two thirds of the tongue project gustatory axons to which cranial nerve?

A

Facial nerve.

56
Q

The posterior third of the tongue projects gustatory axons to which cranial nerve?

A

Glossopharyngeal nerve.

57
Q

The throat region projects gustatory axons to which cranial nerve?

A

Vagus nerve.

58
Q

The peripheral processes of the afferent gustatory neurons from all three cranial nerves synapse with which nucleus?

A

Gustatory nucleus (in the medulla).

59
Q

Why is it presumed that the conscious experience/perception of taste is mediated by the cerebral cortex?

A

The path to the neocortex via the thalamus is common to all of our senses (except olfaction).

60
Q

Describe the pathway for the axons of the secondary/second-order neurons.

A

Project ipsilaterally in the thalamic tract.
Synapse onto a subset of small neurons in the VPM (ventral posterior medial nucleus of the thalamus).

61
Q

Describe the pathway for the axons of the tertiary/third-order neurons.

A

Project through the posterior limb of the internal capsule to the primary gustatory cortex located in Brodmann’s area 36.

62
Q

Name the two hypotheses for the neural coding of taste.

A

Labelled line hypothesis.
Population coding hypothesis.

63
Q

Describe the labelled line hypothesis.

A

We have taste receptor cells for specific tastes.
We have specific transduction mechanisms and gustatory afferent axons.
We have one pathway up to the primary gustatory cortex.

64
Q

How do we know that the labelled line hypothesis is incorrect?

A

While taste receptor cells are specific for different tastes, they become responsive to different tastes once they are beyond the threshold concentration.

65
Q
A

Systems Neuroscience (8 decks)

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