Module 2 - Taste Flashcards

(61 cards)

1
Q

What are taste buds?

A

Clusters of taste receptor cells located mainly on the tongue that detect taste stimuli.

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2
Q

Where are taste receptors primarily located?

A

On the tongue, but also on the soft palate, epiglottis, and upper esophagus.

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3
Q

What is the name of the small structures on the tongue that contain taste buds?

A

Papillae.

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4
Q

What are the three types of papillae that contain taste buds?

A

Fungiform, foliate, and circumvallate papillae.

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5
Q

What type of cell within taste buds actually detects tastants?

A

Taste receptor cells (also called gustatory cells).

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6
Q

How long is the average lifespan of a taste receptor cell?

A

About 10–14 days.

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7
Q

What is the role of type II (receptor) taste cells?

A

They detect sweet, umami, and bitter compounds via G-protein coupled receptors.

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8
Q

What type of receptors detect salty and sour tastes?

A

A: Ion channels: ENaC for salty and H⁺-sensitive channels for sour.

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9
Q

What is the role of the G-protein gustducin in taste?

A

It transduces signals from sweet, umami, and bitter tastants in type II cells.

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10
Q

How are taste signals transmitted to the brain?

A

Via cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus).

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11
Q

What are the five basic taste qualities?

A

Sweet, salty, sour, bitter, and umami.

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12
Q

Which taste receptor types detect sweet, umami, and bitter?

A

G-protein coupled receptors (GPCRs).

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13
Q

Which taste receptor types detect salty and sour?

A

Ion channels.

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14
Q

What receptors are involved in detecting bitter compounds?

A

T2R receptors (a family of ~25 different receptors in humans).

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15
Q

Which ion channel is mainly responsible for detecting salty taste?

A

Epithelial sodium channel (ENaC).

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16
Q

Which ion channel is mainly responsible for detecting sour taste?

A

Proton-sensitive channels, such as PKD2L1.

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17
Q

How do G-protein coupled receptors contribute to taste signaling?

A

They activate intracellular signaling cascades (e.g., via gustducin) leading to neurotransmitter release.

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18
Q

Why are there so many types of bitter receptors (T2Rs)?

A

To detect a wide variety of potentially toxic or harmful bitter compounds.

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19
Q

What makes salty and sour tastes different in their mechanism from other tastes?

A

They involve direct ion flow through channels, rather than receptor-mediated signaling.

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20
Q

How is taste perception modulated by other factors like temperature and texture?

A

These factors influence taste intensity and perception via sensory integration beyond just receptor activation

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21
Q

Where are the trans-membrane proteins for salt receptors located?

A

In the membrane of microvilli that are in contact with saliva.

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22
Q

What creates the membrane potential in salt receptor cells?

A

The difference in concentrations of Na⁺, K⁺, and Cl⁻ ions between the inside and outside of the cell.

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23
Q

What is the resting membrane potential of salt receptor cells and why?

A

Slightly negative, mainly due to a high concentration of Na⁺ ions outside the cell.

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24
Q

How do Na⁺ ions enter salt receptor cells?

A

Through always-open Na⁺ ion channels via passive diffusion.

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25
What happens when Na⁺ ions enter the receptor cell?
The membrane potential becomes less negative, potentially leading to depolarisation.
26
What triggers neurotransmitter release in salt receptor cells?
Ca²⁺ channels open during depolarisation, increasing intracellular Ca²⁺, which causes neurotransmitter release.
27
What compound most commonly elicits a salty taste?
Sodium chloride (NaCl).
28
How does NaCl taste change at low concentrations (0.01–0.03 mM)?
It may taste sweet rather than salty.
29
Which ions can also enter the salt receptor channel?
Lithium (Li⁺) and potassium (K⁺) ions.
30
Why does potassium chloride (KCl) have a complex taste profile?
It can taste sweet, bitter, salty, and sour depending on concentration.
31
How does the anion in a sodium salt affect saltiness perception?
Organic acid salts (like sodium sulfate) taste less salty than sodium chloride.
32
How do sour taste receptors become depolarised?
By an influx of positive ions, including direct entry of H₃O⁺ and blockage of K⁺ outflow.
33
What does increased intracellular Ca²⁺ in sour cells trigger?
Neurotransmitter release and initiation of an action potential.
34
What determines the sour taste response of a stimulus?
Its titratable acidity rather than its pH.
35
Why does titratable acidity matter more than pH for sour taste?
The mouth buffers pH, so the amount of ionisable hydrogen matters more.
36
What type of receptors detect sweet, bitter, and umami tastes?
G-protein coupled receptors (GPCRs), also called 7-TM receptors.
37
How do sweet tastants (like glucose) trigger neurotransmitter release?
They bind to GPCRs, increase cAMP, inhibit K⁺ channels, leading to depolarisation and Ca²⁺ influx.
38
How do bitter tastants (e.g., quinine) activate taste receptors?
By causing release of IP₃, which releases Ca²⁺ from internal stores.
39
What is the mechanism for umami taste detection via GPCRs?
Similar to sweet: binding activates cAMP, inhibits K⁺ channels, causes depolarisation and Ca²⁺-triggered neurotransmitter release.
40
What other mechanism may be involved in umami detection?
Activation of non-selective cation channels that cause depolarisation.
41
Which phenolic compounds are primarily responsible for bitterness in wine?
Flavan-3-ols such as catechin and epicatechin.
42
What type of taste do flavan-3-ols typically elicit in wine?
A bitter taste.
43
How does the polymerization of flavan-3-ols affect their bitterness?
Longer-chain polymers (tannins) are less bitter and more astringent than monomers or dimers.
44
Where are flavan-3-ols primarily found in grapes?
In the skins, seeds, and stems.
45
How many functional human bitter receptors are there?
25 functional receptors.
46
How do people differ in their sensitivity to bitterness?
People vary greatly in their sensitivity due to genetic differences in receptor types and abundance.
47
What is an example of genetic variation affecting bitterness perception?
Some people find PROP intensely bitter; others find it tasteless.
48
49
What are the three major glands that provide saliva?
The three major glands are the parotid gland, the sublingual gland, and the submandibular gland.
50
What are the functions of the parotid gland in saliva production?
The parotid gland produces saliva that contains amylase (a starch-degrading enzyme), proline-rich proteins (PRP), and bicarbonate ions (HCO3-), which help prevent infections and aid in starch digestion.
51
What does the sublingual gland produce?
The sublingual gland produces saliva rich in mucin, a glycoprotein that forms mucus, which acts as a protective lubricant for the mucous membrane in the mouth.
52
What is the role of the submandibular gland in saliva production?
The submandibular gland provides saliva through ducts that open into the floor of the mouth, contributing to lubrication and digestive functions.
53
What role do minor glands and von Ebner glands play in saliva production?
Minor glands, located in the cheeks, produce mucin. Von Ebner glands on the tongue secrete lipase, an enzyme that breaks down fats in food.
54
What is the normal pH range of saliva?
The normal pH of saliva ranges from 6.2 to 7.4.
55
How does saliva respond to the intake of food and wine acids?
When acids from food and wine are consumed, the pH of saliva falls, which activates the salivary flow rate, particularly in the parotid gland. The bicarbonate (HCO3-) ions neutralize the acids, helping maintain a pH above 5.5.
56
Why is maintaining a pH above 5.5 important in the mouth?
Maintaining a pH above 5.5 helps prevent tooth enamel loss (which begins below pH 5.5) and ensures acid receptor sensitivity is maintained, preventing adaptation.
57
What role does amylase play in saliva?
Amylase breaks down starch in the mouth, reducing the viscosity of starch-based foods, which aids in swallowing, releases fats that can be tasted, and enhances flavor release.
58
How does amylase affect the mouthfeel of food?
Amylase reduces the viscosity of foods like bread and pasta, which increases the perceived slipperiness of the food and helps release flavors.
59
What are proline-rich proteins (PRP) and their role in saliva?
PRPs are proteins containing the amino acid proline. They interact with tannins in food and wine, binding to them and reducing astringency.
60
How does PRP in saliva affect tannins in wine?
In red wine, PRP interacts with tannins, leading to the precipitation of wine proteins, which lowers the natural levels of protein in the wine.
61