Chemical Senses Flashcards
Describe what a sense is
built from specialized cells (sensory receptor
cells) that respond to or signal particular physical
phenomena and the corresponding brain networks that receive and interpret those signals
senses detect useful information from the world
Describe the basic hierarchical model of perceptual processing and explain the major steps in this processing
information flows through brain structures in order of their increasing neuroanatomical and functional complexity
RECEPTORS
—-> THALAMUS
—-> S1
—> S2
—> ASSOCIATION CORTEX
- Receptors receive stimuli from environment and transduce it into neural signal
- Subcortical processing occurs in thalamus —> more abstract processing as you move up to primary and secondary sensory cortex and finally association cortex
Explain why we should think of perception as an active process, i.e., on that might involve learning, prediction, expectation, interpretation, etc.
Provide evidence that our perception is not just a matter of taking in information as it is in the world but rather that perception is an active process, relying on things like expectation, learned experience, interpretation, etc.
it’s easy to think that we’re just taking in the
information that’s in the outside world, that our vision
is like a camera, our hearing like a tape recorder
—> but we don’t see/hear/feel/taste information in the
world exactly as it is
perception is an ACTIVE PROCESS
involving PE IRL
• Prediction
• Expectation
• Interpretation
• Reconstruction
• Learning
Define what transduction is
Transduction: converting outside stimuli/input (odorants, sound waves, electromagnetic radiation) into neural signals to be read inside the body
Understand what taste receptor cells, taste buds, and papillae are and where they are
Taste receptors found mostly on tongue, but also
on roof of mouth, pharynx, epiglottis, and part of
esophagus
Taste receptors located in taste cells —> Taste cells cluster into taste buds —> Taste buds cluster together to form papillae (the bumps on our tongue)
taste receptors —> taste cells —> taste buds —> papillae
• Taste cells embedded in taste buds produce
information about the identity, concentration, and
hedonic quality of the food.
• Taste cells also cause salivation
Describe the major tastant categories
major tasting categories:
- Sweet (e.g., sucrose)
- Salty (e.g., NaCl)
- Sour (e.g., citric acid)
- Bitter (e.g., quinine)
- Umami (e.g., MSG)
Describe the ways in which tastants can activate taste receptors and understand the ways this works for each category of tastant, e.g., how salty tastes activate taste
receptors, how sour tastes do, and so on
Salty and sour directly activate ion channels
With salty Na+ flows in and depolarizes
With sour: K+ channels get blocked and K+ stays inside and depolarizes or H+ flows in
Sweet, bitter, and umami all activate metabotropic glutamate receptors
Explain why old models suggesting that we taste specific types of tastants only on certain areas of the tongue are incorrect
x
Describe some of the potential evolutionary reasons why certain tastes seem “hardwired”
and explain how tastes can also be learned
We pretty much all naturally like sweet things because they are caloric (evolutionarily you want calories)
Bitter could mean poison
But also learned “no one is born liking blue cheese”
The fact that we can adapt to like so many things (“it was a brave man who first tried the oyster”) is beneficial; think of the koalas who die because they’ll only eat bamboo
Describe what a supertaster is and what characterizes them
10-25% of the population very sensitive to taste; they can have 100 x more papillae on their tongue
Describe what we know about the genetics of bitter taste
TAS2R38 gene has two common alleles: “tasting” and “non-tasting”
Each allele codes for a bitter taste receptor protein with a slightly different shape; shape determines how strongly bitter chemicals can bind to it.
TT and Tt can taste PTC; tt cannot
Describe the concept of magnitude mapping
Explain why magnitude mapping is a useful way to study supertasters
Magnitude mapping involves describing intensity of one sense in terms of another sense
“how intense is the sweetness of this soda in terms of intensity of sound”?
This methods gets super taster to answer ‘louder’ than non-super tasters
Describe the methods, results (behavioral and fMRI), and significance of the experiment looking at the effects of price information on the taste experience of wine
They presented five wines; two were presented twice with different price tags attached, the other one presented once with real price
Participants regularly ranked the more expensive wine, the exact same wine, as tasting better
fMRI revealed they also experienced the more expensive wine as tasting better; there was greater activity in the medial orbitofrontal cortex when tasting same wine with higher price
when given no prices (to the same participants later) no difference in liking of the same wines
Describe something the medial orbitofrontal cortex seems to signal and be able to roughly locate that area in the brain
It deals with valuation
Describe the methods, results, and significance of the beer + balsamic vinegar study
Went to a bar in Cambridge
Gave people a lager with balsamic vinegar added with three different categories
No info; info before trying; info after trying
Only (negatively) affected experience/opinion if you knew before
Describe what happens people eat a miracle berry and then eat certain foods
miraculin binds to sweet taste receptors as an antagonist at a neutral pH and functionally changes into an agonist at acidic pH
(it activates sweet receptor cells when in contact with sour things -> it makes sour things taste sweet)
Provide evidence that our perception is not just a matter of taking in information as it is in the world but rather that perception is an active process, relying on things like expectation, learned experience, interpretation, etc.
x
Describe what retronasal olfaction is and how it contributes to taste
Retronasal smelling involves smelling, during exhalations, odorants originating from the oral cavity
Your mouth is connected to your nasal cavity. As you chew, odorants travel from your mouth to your nose.
Flavor is thus derived from much more than just taste (remember the starburst!)
Describe what anosmia is
loss of sense of smell, typically caused by head injury, infection, or blockage of the nose.
Identify on a diagram and describe the role of the major components of the olfactory system: olfactory epithelium, cribriform plate, glomeruli, olfactory bulb, primary olfactory cortex (rhinencephalon or pyriform cortex)
x
Name what type of receptors odorants bind to
metabotropic receptors
Describe the process of pattern encoding
It is not a one to one ratio; one type of olfactory receptor does not equate to one smell
Rather, the (unique) pattern of activation of those different receptors constitutes a particular smell
Explain why pattern encoding is such a useful way of encoding information coming in to taste and smell receptors
x
Think about what we discussed in class as well as the New Yorker article and provide examples of how taste and flavor can be affected my many other factors
x
Describe how information is organized in glomeruli and where that information gets sent
x
If given a prompt like, “You pick up a cup of coffee in front of you. First, you smell it and then you take a sip. Describe how the odor and tastant molecules are understood by the brain as the smell and taste of coffee,” be able to describe what happens along the
olfactory and gustatory pathways at each step of the way, e.g., what are the sensory receptors where transduction occurs, what’s happens next, and after that and so on until you get to the primary sensory cortex and secondary or tertiary cortices (you only need to describe this in the level of detail we discussed in class, e.g., we didn’t talk much about secondary or tertiary cortices for smell, so you wouldn’t be responsible for that, though it would be good to understand that the location of the primary olfactory cortex – as well as the fact the smell information doesn’t go through the thalamus – makes connections with areas like the amygdala and hippocampus more direct)
x
What do secondary and tertiary cortices do, broadly speaking?
x
