Gustation

Question 1

What defines a sense?

Answer 1

A group of sensory cells
that responds to a specific physical
phenomenon, and that corresponds to a particular region of the brain where the signals are received and interpreted.

Question 2

Who studies senses?

Answer 2

Johannes Muller (19th century) - Handbook of Physiology; doctrine of specific nerve energies

Hermann Ludwig Ferdinand von
Helmholtz - disproved vitalism (non-physical forces); supported physical forces explaining behaviour by measuring neuron activities

Santiago Ramon y Cajal & Sherrington - neurons don’t touch each other; synapses do.

Otto Loewi - neuron transmissions are chemical-based; there are excitatory (capsaicin, which is warm) & inhibitory (menthol, which is cooling) neurons

Question 3

What are the electrophysiological methods?

Answer 3

Recording a single cell. Hubel & Wiesel (1981) fed monkeys sweet and sour items and recorded how a single cell in their brains responded. Mostly done on animals.

Question 4

Who is the father of experimental psychology?

Answer 4

Gustav Fechner

Question 5

How did Fechner contribute to experimental psychology?

Answer 5

Instigated debate of mind vs matter

Question 6

How did Ernst Weber contribute to experimental psychology?

Answer 6

Studied how environmental stimuli is translated into psychological experience quantitatively

Question 7

What are the units of experimental psychology?

Answer 7

Absolute thresholds - minimum energy that can be detected by a sensory modality

JND - just noticeable difference (minimum energy required to be perceived differently in intensity)

Question 8

What are the three classic psychophysical methods?

Answer 8

Method of Limits - present stimuli in ascending / descending order, then tell when you detect

Method of Constant Stimuli - present a set of stimuli multiple times in
random order, then ask to detect

Method of Adjustment - allow participant to adjust the stimuli until they sense / perceive it

Question 9

What is Fechner’s Law?

Answer 9

aka Weber’s Contrast (Ψ = k logS), the relation between the actual change in a physical stimulus and perceived change

Question 10

What do the scaling methods measure?

Answer 10

Magnitude of sensory experience and magnitude estimation based on Steven’s law; power relationship

Question 11

What are some neuroimaging methods?

Answer 11

EEG / MEG / MRI

Question 12

How do we define neuroimaging methods?

Answer 12

Modern science that understands how sensory cortices respond to stimuli.

Question 13

How many taste qualities are there?

Answer 13

Five.
1) Sweet – sucrose, saccharine, aspartame (calories)

2) Sour – Citric acid, acetic acid (warns of spoilage or unripeness)

3) Salty – Sodium Chloride (electrolytes to maintain body fluid balance)

4) Bitter – Alkaloids (eg. Caffeine) (poison)

5) Umami – Monosodium Glutamate (protein)

Question 14

What are the taste developments?

Answer 14

As early as 7 or 8th week of gestation – specialised
taste cells

Structurally mature taste buds visible at 13-15
weeks

Taste receptors are stimulated by chemicals in
amniotic fluid

Infants may have up to five times the amount of
taste buds adults have. Foliate papillae are larger
and more abundant

Question 15

How is taste perceived?

Answer 15

Tongue –> Papillae –> Taste Bud –> Taste Receptor
–> Depolarization of taste cell –> Cascade of messages to brain

Question 16

What does papillae consist of>

Answer 16

1) Filiform: Upper surface of
tongue (no taste buds)

2) Fungiform: >100 on each side
of tongue. 2-4 taste buds
each.

3) Foliate: Groove on side of
tongue. Several 100 taste
buds.

4) Circumvallate: ~7 in V-shape
in back of tongue. Several
hundred taste buds each.

Question 17

Where are tastebuds located?

Answer 17

In the papillae.

Question 18

Why does the filiform not have taste buds?

Answer 18

Create rough texture on the tongue surface, to help with perception

Question 19

What are tastebuds and their function?

Answer 19

Special sense organs that contain receptors for the
sense of taste

Question 20

What percentage of tastebuds are on the papillae?

Answer 20

Around 75%

Question 21

How long does a taste receptor survive?

Answer 21

Contained within taste buds, they last about a week. 30 - 50% die every week.

Question 22

What does a tastebud have?

Answer 22

50/100 columnar epithelial cells (Type I, II & III) + basal cells + neuronal processes

Question 23

What type of compounds contribute to the salty taste?

Answer 23

NaCl and other Na+ containing compounds

Question 24

Which taste receptor cells sense salt?

Answer 24

Type I and II taste receptor cells

Question 25

How does Na+ stimulate the taste receptor cells?

Answer 25

Na+ enters the cell, increasing intracellular Na+, which depolarises the membrane.

Question 26

What happens after the taste cell membrane is depolarised?

Answer 26

A voltage dependent Ca++ channel opens.

Question 27

How does Ca++ contribute to taste transduction for salt?

Answer 27

Increased Ca++ in the cell triggers the release of neurotransmitters.

Question 28

What are the three classes of Taste Receptor Cells(TRC)?

Answer 28

Type 1:detects low salt Type 2:detects high salt, sweet, bitter, umami, and kokumi Type 3:detects sour

Question 29

Which nerve conducts taste signals from the front and sides of the tongue, particularly the fungiform papillae?

Answer 29

Chorda tympani nerve

Question 30

Which nerve conducts signals from the back of the tongue?

Answer 30

Glossopharyngeal nerve

Question 31

which nerve conducts taste signals from receptors in the mouth and larynx?

Answer 31

Vagus nerve

Question 32

Why is the sense of taste considered robust compared to other sensory modalities?

Answer 32

Because different nerves innervate the tongue, ensuring multiple pathways for taste perception.

Question 33

What is the primary taste cortex?

Answer 33

Insula-f0

Question 34

What is the secondary taste cortex?

Answer 34

OFC

Question 35

What are the tongue consisted of?

Answer 35

Taste buds, taste receptor cells, tastant receptors

Question 36

Where is nucelus tractus solitarius located?

Answer 36

Brain stem nuclei

Question 37

How is taste information encoded en route to the brain?

Answer 37

Labelled line hypothesis-individual TRCs encode a single taste quality and synpase with afferent fibres that are also dedicated to that quality. Combinatory model-information is transmitted by combinatorial activity in multiple fibres. Overall, combination of fibres activated encodes the taste quality.

Question 38

What are the two options for the combinatorial model?

Answer 38

Option1: TRCs have multiple receptors, so send mixed messages down one sensory fibre. Option2: TRC of one kind has 1 kind of receptor, but multiple TRCs innervate a single sensory fibre.

Question 39

what is the supporting evidence for labelled lines model?

Answer 39

Some sensor fibres respond best to one tastant.

Question 40

What is the supporting evidence for the combinatorial mode?

Answer 40

-Taste buds contain both narrowly tunned cells and more broadly responsive ones(type 2 vs type 3, etc) -Sensory fibres can be broadly tunned or narrowly responsive(i.e responsive to one or multiple tastants)

Question 41

How does gustatory system transfer the signals?

Answer 41

Brain stem nuclei--->thalamus---->primary taste cortex(insula-f0)--->Secondary cortex(OFC)

Question 42

What is the controversy of the two theories?

Answer 42

Scientist argues that possibly even specialist and generalist neurons in the brain stem in the relay station. This is impossibly true because there is no evidence of rate coding in TRCs or sensory afferents of the gustatory system.

Question 43

What is the predominant taste of hydrochloric acid(HCl)?

Answer 43

Sour

Question 44

What is the predominant taste of sucrose?

Answer 44

Sweet

Question 45

What is the predominant taste of sodium chloride(NaCl)?

Answer 45

Salty, but at low concentrations, it can taste sweet.

Question 46

Do most compounds have only one taste quality?

Answer 46

No, most compounds have more than one taste quality.

Question 47

What are the taste qualities of potassium chloride(KCl)?

Answer 47

Substantial salty and bitter taste.

Question 48

What are the taste qualities of sodium nitrate(NaNO3)?

Answer 48

Salty, sour, and bitter.

Question 49

Why there is a long debate about where exactly is the primary taste cortex?

Answer 49

1. Taste hardly occurs by itself. 2. They only found there is only 5 to 10 neurons respond to taste. 3. Neuroimaging using different psychophysic methods which made it hard to compare.

Question 50

what do we use to decode insula?

Answer 50

-EEG+ Psychophysics -MVPA-as analysis -taste quality discrimination relied on transient large scale neural response patterns.

Question 51

What is the Group level taste conjunctions

Answer 51

Conjunction analyses of taste contrasts provide no clear evidence of topographical organisation. At the group level, whole brain conjunctions of taste contrasts, using corrected statistical contrasts, they did not identify any voxel within the insula. Identify voxels within the insula or the wider brain exhibiting a significant preference for either sweet, sour, or slaty taste.

Question 52

Subject level conjunctions

Answer 52

At the subject level, a similar series of taste specificity analyses identified distributions of voxels within the insula that exhibited a selective preference for specific tastes. However,the distribution of voxel was not consistent across the subjects nor were the dominant in the any consistent pattern.

Question 53

What is ageusia?

Answer 53

Total loss of taste(rare)

Question 54

What is hypogeusia, and what are some causes?

Answer 54

Decreased sensitivity to taste,often due to aging, zinc deficiency, or vitamin B3deficiency.

Question 55

What is hypergeusia, and what condition is it as associated with?

Answer 55

Increased sensitivity to taste, associated with Addison's disease.

Question 56

What is dysgeusia, and what condition can cause it?

Answer 56

Unpleasant taste sensitivities, often linked to cancer.

Question 57

How does age affect taste sensitivity?

Answer 57

Sensitivity generally decline with aging.

Question 58

What factor besides age might influence taste sensitivity?

Answer 58

Genetics.

Question 59

what are two compounds used to study genetic influence on taste?

Answer 59

phenylthiocarbamide(PTC) is the chemical version of 6-n-propylthiouracil(PROP)

Question 60

What percentage of people can taste PROP?

Answer 60

75% are tasters, including 25% who are super tasters.

Question 61

What percentage of people are non-tasters for PROP?

Answer 61

25%

Question 62

Which gene determines an individual's perception of PROP and PTC?

Answer 62

TAS2R38(taste receptor 2 member 38)