Chapter 16: The Chemical Senses Flashcards
anosmia
the loss of the sense of smell due to injury or infection
negative consequences of anosmia
- Loss of the pleasure of eating
- Loss of the pleasure of socializing
- Feelings of isolation
- Lack of motivation to eat
- Becoming more prone to hazardous events
taste
occurs when molecules enter the mouth in solid or liquid form and stimulate receptors on the tongue
olfaction
occurs when airborne molecules enter the nose and stimulate receptor neurons in the olfactory mucosa
flavour
the impression we experience from the combination of taste and olfaction
where do the chemical senses occur?
right at the beginning of the systems when the receptors are stimulated
neurogenesis
the constant renewal of smell and taste receptors
life cycle of olfactory receptors
5-7 weeks
life cycle of taste receptors
1-2 weeks
why are the chemical senses called gatekeepers?
- they identify things the body needs for survival and that should be consumed
- they detect things that would be bad for the body and should not be consumed
how are the chemical senses are distinct from other senses
- Sensory receptors are exposed to the environment
- They have shorter life cycles
5 basic taste sensations
salty, sour, sweet, bitter, and umami
McBurney, 1969 taste quality experiment
presented taste solutions to participants and asked them to make magnitude estimates of the intensity of each of the four taste qualities for each solution. Found that some substances have a predominant taste quality while others result in combinations of the basic taste qualities
sweetness is associated with
substances that have a nutritional or caloric value
what response is associated with sweetness?
acceptance response and triggers anticipatory metabolic responses
bitterness is associated with
harmful substances
what response is associated with bitterness?
automatic rejection responses to help the organism avoid the substance
saltiness is associated with
the presence of sodium
function of saltiness
Allows the body to replenish its salt content`
papillae
ridges and valleys on the tongue, some of which contain taste buds
4 types of papillae
filiform papillae, fungiform papillae, foliate papillae, and circumvallate papillae
Filiform papillae
shaped like cones and are found over the entire surface of the tongue, giving it its rough appearance
Fungiform papillae
shaped like mushrooms and are found at the tip and sides of the tongue
Foliate papillae
series of folds along the back of the tongue on the sides
Circumvallate papillae
shaped like flat mounds surrounded by a trench and are found on the back of the tongue
what papillae contain taste buds?
All papillae except the filiform papillae
taste buds
structures located within the papillae on the tongue that contain the taste cells
how many taste buds does the tongue contain?
10,000
how many taste cells does each taste bud contain?
50-100
taste cells
cells that cause the transduction of chemical to electrical energy when chemicals contact receptor sites or channels located at the tip of this cell
taste pore
an opening in the taste bud through which the tips of taste cells protrude. When chemicals enter a taste pore, they stimulate the taste cells and result in transduction
4 ways signals generated in the taste cells are transmitted from the tongue to the brain
- The chorda tympani nerve
- The glossopharyngeal nerve
- The vagus nerve
- The superficial petrosal nerve
The chorda tympani nerve
from taste cells on the front and sides of the tongue
The glossopharyngeal nerve
from the back of the tongue
The vagus nerve
from the mouth and the throat
The superficial petrosal nerve
from the soft palate (top of the mouth)
across-fibre patterns
another word for population coding
Erickson, 1963 rats and population coding experiment
If he shocked rats while they were drinking one of the 3 substances, he found that they would avoid it and choose one of the others in subsequent trials.
Schiffman & Erickson, 1971 humans and population coding experiment
in humans, solutions judged as more psychophysically similar had similar patterns of firing
counter-evidence for population coding
using different behavioural tests, mice that no longer have a sweet receptor still have a preference for sugar
PTC & genetic cloning in mice
mice don’t have PTC receptors, so they don’t find it bitter like humans do. However, using genetic cloning to input a PTC receptor, we can get mice to avoid PTC
Cyx & genetic cloning in mice
mice have Cyx receptors and avoid them. However, using genetic cloning, we can remove the receptor so that they no longer avoid it
are neurons in the taste system specialized?
Recordings from neurons at the beginning of taste systems are specialized to respond to specific stimuli, but some neurons respond to many different types of stimuli
Amiloride
blocks the flow of sodium into taste receptors
what happens when amiloride is applied to rat’s tongues?
Applying amiloride to the tongue blocks the flow of sodium to taste receptors and causes a decrease in responding of neurons in the rat’s brainstem that respond to salt
what type of coding is used in the taste system?
Most researchers favour specificity coding, but the debate isn’t resolved
Tasters
people who can taste a given substance
nontasters
people who can’t taste a given substance
humans vs. cat’s taste
Cats are blind to sweet tastes
supertasters
people who are especially sensitive to a particular substance
PROP & PTC differences in taste
PROP & PTC specialized receptors are absent in non-tasters (about 1/3 of people)
what is one of the most common individual taste differences?
differences in the perception of the sweetness of sucrose
Micosmatic
having a poor sense of smell that is not crucial to survival
Macrosmatic
having a well-developed sense of smell
humans’ smell is ____
Macrosmatic
do humans have a sensitive sense of smell?
yes; we can discriminate between more than 1 trillion olfactory stimuli
detection threshold
the lower concentration at which an odorant can be detected
forced-choice method
participants are presented with one weak odorant and one no odorant and must determine which has the stronger smell. The threshold is determined as the concentration that results in a correct response in 75% of trials
are humans good at identifying specific odours?
no
does knowing the correct label for an odour influence our perception of it?
yes
B-ionone in sensitive vs. nonsensitive individuals
- Individuals more sensitive to B-ionone describe it as fragrant
- Individuals less sensitive to B-ionone describe it as sour
effect of genetics on smell
Some genetic conditions cause the selective loss of some smells
perception of androsterone
it’s described positively, neutrally, or negatively depending on the person
why is odour identification so difficult?
- We lack a specific language for odour quality
- Molecules that have similar structures can smell very differently, while molecules that have very different structures can smell very similarly
- Most of the odours we encounter consist of a mixture of many different chemicals
- Odours rarely occur in isolation
odour objects
sources of odour
two stages of perceiving odour
- Analyzing the different chemical components of odours and transforming these components into neural activity at specific places in the olfactory bulb
- Synthesizing information about the chemical components received from the olfactory bulb into representations of odour objects
where does analyzing odour take place?
in the olfactory mucosa and the olfactory bulb
where does synthesizing odour take place?
in the olfactory cortex and beyond
Olfactory mucosa
a dime-sized region at the top of the nasal cavity that contains receptors for smell
Olfactory bulb
the structure that receives signals directly from the olfactory receptors.
Olfactory receptor neurons (ORNs)
sensory neurons located in the olfactory mucosa that contain the olfactory receptors
Olfactory receptors
a protein string that responds to odour stimuli
how many different types of olfactory receptors are there?
400
how many different olfactory receptors do ORNs contain?
1
calcium imaging
measures the increase in calcium ions inside the olfactory receptor that occurs when it responds by soaking olfactory neurons in a chemical that causes the ORN to fluoresce with a green glow when exposed to ultraviolet light. Increasing Ca+ inside the neuron decreases the glow, providing a measure of how much Ca+ has entered the neuron
recognition profile
the pattern of activation of individual receptors for a particular odorant
how are odorants coded?
by a different pattern of firing of ORNs
how many odorants does an ORN respond to?
many
glomeruli
small structures in the olfactory bulb that receive signals from similar olfactory receptor neurons. Each glomerulus collects information about a small group of odorants
Chemotopic/ odour/odotopic maps
the pattern of activation in the olfactory system in which chemicals with different properties create a map of activation based on these properties
what kind of properties are chemotopic/ odour/odotopic maps based on
chemical properties
Piriform cortex (primary olfactory area)
an area under the temporal lobe that receives signals from the glomeruli in the olfactory bulb
Orbitofrontal cortex (secondary olfactory area)
an area in the frontal lobe, near the eyes that receives signals originating in the olfactory receptors
amygdala
involved in determining emotional reactions to smell, faces, and pain
how are odorants organized in the piriform cortex?
the chemotopic map vanishes and there is an overlap between the activity caused by different odorants
Functional ultrasound imagery
determines brain activation by measuring changes in blood flow
how does learning affect the formation of the odour?
The formation of odour objects involves learning, which links together scattered activations of a particular object
when are odour objects formed
when experience with an odour causes neurons in the piriform cortex to become activated
Wilson, 2003 piriform cortex and odour discrimination experiment
measured the response in the rat’s piriform cortex to two odorants (a mixture and a compound). Found that given enough time, neurons in the piriform cortex can learn to discriminate between different odours and that this learning may be involved in our ability to differentiate between odours in the environment
Nucleus of the solitary tract
where the fibres from the tongue, mouth, and throat connect
umami
described as meaty, brothy, or savoury, and associated with MSG
the tongue map
a myth that depicts where in the tongue particular taste qualities are detected
3 components of the chemical senses
taste, olfaction, and flavour
emotional components of the chemical senses
- Things that are bad for us often taste or smell unpleasant
- Things that are good for us generally taste or smell good
- Smelling an odour associated with a past place or event can trigger memories, which in turn may create emotional reactions
descriptors of taste
- Onset/aftertaste
- Intensity
- Quality
- Hedonics (pleasant vs. unpleasant)
- Localization
4 taste qualities
- Sodium chloride (salty)
- Hydrochloric acid (sour)
- Sucrose (sweet)
- Quinine (bitter)
taste qualities of potassium chloride (KCl)
has substantial salty and bitter components
taste qualities of sodium nitrate (NaNO3)
results in a taste consisting of a combination of salty, sour, and bitter
is there a connection between the tastes and functions of substances?
There is not a perfect connection between the tastes and functions of substances
when does gustatory transduction take place?
when chemicals contact the receptor sites on the tips
where do signals from the gustatory pathways go?
These pathways make connections in the nucleus of the solitary tract in the spinal cord. Then they travel to the thalamus, followed by areas in the frontal lobe, including the insula, frontal operculum cortex, and the orbitofrontal cortex
population coding
Quality is signalled by the pattern of activity distributed across many neurons
taste buds & receptors in tasters vs. non-tasters
Tasters have more taste buds and specialized receptors
supertasters and bitter substances
Supertasters appear more sensitive to bitter substances than tasters. As a result, they’ll eat less vegetables. They have a lower body weight. They’re less likely to drink alcohol & smoke
yes/no procedure
participants are given trials with odours along the blank trails. They respond by saying yes or no
disadvantages of the yes/no procedure
can result in bias in terms of when the participants decide to respond
odour sensitivity of rats vs. dogs. vs. humans
- Rats are 8-50 times more sensitive to odours than humans
- Dogs are 300-10,000 times more sensitive than humans
why are dogs better at smelling than humans?
The difference lies in the number of receptors they each have. Humans have ten million and dogs have one billion olfactory receptors
the puzzle of olfactory quality
Researchers have found it difficult to map perceptual experience onto physical attributes of odorants. There is no specific language for odour quality
proteins in olfactory receptors
Each receptor has a protein that crosses the membrane 7 times
Rennaker study
used multiple electrodes to measure neural responding in the piriform cortex and found that isoamyl acetate causes activation across the cortex
