Gustation Flashcards
What defines a sense?
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.
Who studies senses?
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
What are the electrophysiological methods?
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.
Who is the father of experimental psychology?
Gustav Fechner
How did Fechner contribute to experimental psychology?
Instigated debate of mind vs matter
How did Ernst Weber contribute to experimental psychology?
Studied how environmental stimuli is translated into psychological experience quantitatively
What are the units of experimental psychology?
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)
What are the three classic psychophysical methods?
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
What is Fechner’s Law?
aka Weber’s Contrast (Ψ = k logS), the relation between the actual change in a physical stimulus and perceived change
What do the scaling methods measure?
Magnitude of sensory experience and magnitude estimation based on Steven’s law; power relationship
What are some neuroimaging methods?
EEG / MEG / MRI
How do we define neuroimaging methods?
Modern science that understands how sensory cortices respond to stimuli.
How many taste qualities are there?
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)
What are the taste developments?
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
How is taste perceived?
Tongue –> Papillae –> Taste Bud –> Taste Receptor
–> Depolarization of taste cell –> Cascade of messages to brain
What does papillae consist of>
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.
Where are tastebuds located?
In the papillae.
Why does the filiform not have taste buds?
Create rough texture on the tongue surface, to help with perception
What are tastebuds and their function?
Special sense organs that contain receptors for the
sense of taste
What percentage of tastebuds are on the papillae?
Around 75%
How long does a taste receptor survive?
Contained within taste buds, they last about a week. 30 - 50% die every week.
What does a tastebud have?
50/100 columnar epithelial cells (Type I, II & III) + basal cells + neuronal processes
What type of compounds contribute to the salty taste?
NaCl and other Na+ containing compounds
Which taste receptor cells sense salt?
Type I and II taste receptor cells
How does Na+ stimulate the taste receptor cells?
Na+ enters the cell, increasing intracellular Na+, which depolarises the membrane.
What happens after the taste cell membrane is depolarised?
A voltage dependent Ca++ channel opens.
How does Ca++ contribute to taste transduction for salt?
Increased Ca++ in the cell triggers the release of neurotransmitters.
What are the three classes of Taste Receptor Cells(TRC)?
Type 1:detects low salt
Type 2:detects high salt, sweet, bitter, umami, and kokumi
Type 3:detects sour
Which nerve conducts taste signals from the front and sides of the tongue, particularly the fungiform papillae?
Chorda tympani nerve
Which nerve conducts signals from the back of the tongue?
Glossopharyngeal nerve
which nerve conducts taste signals from receptors in the mouth and larynx?
Vagus nerve
Why is the sense of taste considered robust compared to other sensory modalities?
Because different nerves innervate the tongue, ensuring multiple pathways for taste perception.
What is the primary taste cortex?
Insula-f0
What is the secondary taste cortex?
OFC
What are the tongue consisted of?
Taste buds, taste receptor cells, tastant receptors
Where is nucelus tractus solitarius located?
Brain stem nuclei
How is taste information encoded en route to the brain?
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.
What are the two options for the combinatorial model?
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.
what is the supporting evidence for labelled lines model?
Some sensor fibres respond best to one tastant.
What is the supporting evidence for the combinatorial mode?
-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)
How does gustatory system transfer the signals?
Brain stem nuclei—>thalamus—->primary taste cortex(insula-f0)—>Secondary cortex(OFC)
What is the controversy of the two theories?
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.
What is the predominant taste of hydrochloric acid(HCl)?
Sour
What is the predominant taste of sucrose?
Sweet
What is the predominant taste of sodium chloride(NaCl)?
Salty, but at low concentrations, it can taste sweet.
Do most compounds have only one taste quality?
No, most compounds have more than one taste quality.
What are the taste qualities of potassium chloride(KCl)?
Substantial salty and bitter taste.
What are the taste qualities of sodium nitrate(NaNO3)?
Salty, sour, and bitter.
Why there is a long debate about where exactly is the primary taste cortex?
- Taste hardly occurs by itself.
- They only found there is only 5 to 10 neurons respond to taste.
- Neuroimaging using different psychophysic methods which made it hard to compare.
what do we use to decode insula?
-EEG+ Psychophysics
-MVPA-as analysis
-taste quality discrimination relied on transient large scale neural response patterns.
What is the Group level taste conjunctions
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.
Subject level conjunctions
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.
What is ageusia?
Total loss of taste(rare)
What is hypogeusia, and what are some causes?
Decreased sensitivity to taste,often due to aging, zinc deficiency, or vitamin B3deficiency.
What is hypergeusia, and what condition is it as associated with?
Increased sensitivity to taste, associated with Addison’s disease.
What is dysgeusia, and what condition can cause it?
Unpleasant taste sensitivities, often linked to cancer.
How does age affect taste sensitivity?
Sensitivity generally decline with aging.
What factor besides age might influence taste sensitivity?
Genetics.
what are two compounds used to study genetic influence on taste?
phenylthiocarbamide(PTC) is the chemical version of 6-n-propylthiouracil(PROP)
What percentage of people can taste PROP?
75% are tasters, including 25% who are super tasters.
What percentage of people are non-tasters for PROP?
25%
Which gene determines an individual’s perception of PROP and PTC?
TAS2R38(taste receptor 2 member 38)
