Chemical senses Flashcards
1
Q
what are chemical senses?
A
- Molecules attach to specialised receptors in mouth (taste) and nasal cavity (smell).
2
Q
what is smell vs odour?
A
- Smell and odour are the same and are used interchangeably.
- Odour and odour thresholds can widely for different compounds:
- Hydrogen sulphide (‘rotten eggs’ – 0.0005 parts per million ppm),
- Cyclohexane (‘ether-like’ – 83.8 ppm)
- Difference in threshold concentrations between the two is about ×170,000
3
Q
what are odourless killers?
A
- Some dangerous gases (e.g. carbon monoxide) are odourless.
- Natural gas is odourless, but mercaptans (combination of carbon, hydrogen, and sulfur; smell like garlic) are added to improve leak detection.
4
Q
how do we adapt to smells?
A
- Dalton and Wysocki: adapt to citralva, test every 30 seconds, citralva (lemon) or iso bornyl acetate (pine).
- The effects of 2 weeks of exposure/adaptation last for at least 2 weeks after.
5
Q
how do foetus’ learn odours from mothers?
A
- Schaal et al. (2000) measured the olfactory responsiveness in 24 neonates born to mothers who had or had not consumed anise flavour during pregnancy.
- Infants born to anise-consuming mothers evinced a stable preference for anise odour over this period (a), whereas those born to anise non-consuming mothers displayed aversion or neutral responses (b-d).
6
Q
how do we smell?
A
- Odourants are first dissolved in the mucus lining the olfactory epithelium.
- They are then carried by odourant binding proteins (OBPs) that:
- take them to the olfactory receptor neurons (ORNs) and
- remove them for degradation. - Signals are then sent to the olfactory bulb.
7
Q
what is bottom-up vs top-down in smell?
A
- Many molecules create a single smell perception.
- Odours occur concurrently but the perceptual system can separate them from one another (Gestalt).
- Past experience and expectations have an impact on odour perception.
- Thus, odour perception is both a bottom-up process and top-down process.
7
Q
what is the orbital frontal cortex in smell?
A
- De Araujo et al. (2005) exposed participants to:
- Condition 1: A mixture of a sweat-like smell and a cheddar cheese flavouring.
- Condition 2: Clean air - In both conditions, participants saw the label “cheddar cheese,” on some trials and the label “body odour” on others.
- Pleasantness ratings were higher for the cheddar cheese trials. OFC activity correlated with the pleasantness ratings.
8
Q
what are the functions of smell?
A
- Ingestion: Detecting and identifying substances to be ingested; identifying substances in the mouth which may be contaminated; Regulating of appetite.
- Avoiding environmental hazards: Detecting predators, fire, signs of air- or water-borne contaminants, faeces, urine or vomit.
- Social communication: Facilitating reproduction, including avoidance of in-breeding and mate-selection; detecting fear-related cues).
- Regulation of appetite: Olfactory thresholds can rise with BMI (Skrandies & Zschieschang, 2015).
- Navigating through space: Humans can use olfactory cues for guide themselves (Bao et al., 2019) .
- Facilitates attention: Search for banana is better if accompanied by banana aroma rather than rose (Chen et al, 2013).
9
Q
what are pheromones?
A
- Pheromones comes from the Greek words “pherein” (to carry or transfer) and “hormon” (to stimulate or excite).
- Karlson and Luscher (1959) first described them as “substances secreted to the outside by an individual and received by a second individual of the same species, in which they release a specific reaction, for example, a definite behavior or a developmental process.”
- Most mammals have secondary olfactory system, the vomeronasal organ (VNO) with input from receptors in that are sensitive to pheromones. In humans, existence and function of the VNO have been disputed.
10
Q
what is odourtype?
A
- Each individual has a smell that is determined by your immune system, and we all have a unique immunotype determined by our Human Leucocyte Antigen (HLA) molecules (Eggert et al., 1999).
- We can recognise family members with odourtype and we tend not to like smell of our opposite gender siblings and parents anti-incest device
11
Q
what is odourtype with mother and babies?
A
- Kaitz et al. (1987) showed that
- 90% of women can identify their babies’ smell after 10 minutes to 1 hour of exposure.
- 3-hour-old babies can discriminate a gauze pad worn by their mother and one worn by another mother.
12
Q
how does odourtype and mate selection work?
A
- Wedekind et al. (1997) found that women prefer male odours that differ from their own odourtypes.
- They also reported that the odour of HLA-dissimilar men reminded female subjects of their former partners (more than the odour of HLA-similar men; Wedekind et al., 1995).
13
Q
how do odourtype work in art?
A
- Augier (2007) suggested that this could be the new way blind dating agencies can match individuals with a suitable partner for procreation.
14
Q
what is the point on smelling nice?
A
- Singh and Bronstad (2001) presented men with T-shirts worn overnight by women in ovulatory and non-ovulatory phases, and asked them to rate the smells in terms of intensity, pleasantness and sexiness.
- They found higher ratings for pleasantness and sexiness (but not intensity) for ovulatory phase.
- They suggested that smells can cue fertility.
15
Q
what is the role of testosterone in smell?
A
- Miller and Maner (2010) examined testosterone response to olfactory ovulation cues.
- Men were asked to rate T-shirts worn by women at different phases of menstrual cycle, and the concentrations of testosterone in their saliva just and 15 minutes after smelling the shirts was also recorded.
- The researchers found that testosterone levels were higher after the men had smelled “ovulatory” T-shirts, and suggested that olfaction affects hormonal responses in males which increase probability of mating.
16
Q
what is the importance of fragrance preference?
A
- Milinski and Wedekind (2001) showed that there is a positive correlation between your fragrance preference and your personal odourtype.
- We prefer perfumes with key ingredients that accentuate our HLA.
17
Q
what role does smell have on the menstrual cycle?
A
- Stern and McLintock (1998) rubbed swabs from armpits of females at different stages of menstrual cycle, applied to upper lips of other females.
- They found that the timing of ovulation can be manipulated by pheromones: Ovulatory swabs lengthened the cycle of the recipient, but Follicular swabs shortened the cycle.
18
Q
can you smell fear?
A
- Ackerl et al., 2002 collected Armpit secretions from individuals who had just watched a neutral or a horror movie and asked participants to rate the samples:
19
Q
when are we introduced to taste?
A
- Rosenstein and Oster (1988) showed that human infants, as young as 2h-old, are hard-wired to detect taste.
20
Q
what are the 5 basic tastes?
A
- Sweet
- Associated with glucose and high energy food. - Salty
- Associated with sodium (Na) - Bitter
- Associated with poison - Sour
- Associated with acids - Umami
- Described as meaty, brothy or savoury and comes from the Japanese word “good taste”
21
Q
is there a sixth primary tasta?
A
- Fatty acids are a potent taste stimuli and there are receptors that detect them in taste buds (Mattes, 2009).
- There is evidence that there is a region in the oral somatosensory cortex that responds to high-fat more than to low-fat taste receptors (Grabenhorst & Rolls, 2014).
22
Q
what is the tongue papillae
A
- These are tiny bumpy structure and there are two categories on your tongue:
- The Fungiform, Circumvallate, and Foliate papillae are involved in taste perception and contain taste buds.
- The Filiform are involved in moving food around and in detection textures. These are the most numerous. They do not contain taste buds.
23
Q
where are the locations of taste buds?
A
- Fungiform (mushroom-shaped) on tip and sides of tongue.
- Circumvallate form semicircle at base of tongue.
- Foliate papillae are ridges and grooves on the rear lateral margins of the tongue.
- Taste buds also found on soft palate, upper oesophagus and epiglottis.
24
Q
how do signals go from the tongue to the brain?
A
- Signals from taste cells travel along a set of pathways:
- Chorda tympani nerve from front and sides of tongue
- Glossopharyngeal nerve from back of tongue
- Vagus nerve from mouth and throat
Superficial petronasal nerve from soft palate
25
Q
what are the specific fibres for specific chemicals?
A
- Sato et al. (1975) recorded the activity of 67 fibres in the monkey’s chorda tympani and found:
- 66% responsive to NaCl – salty
- 55% to HCl – sour
- 48% to sucrose – sweet
- 33% to quinine – bitter
- 23 of 67 responsive to one
- 24 to two
-16 to three - 4 to all the four basic stimuli.
- Also sensitive to temperature!
- A variety of fibres with a variety of sensitivities.
26
Q
what are the two theories for taste coding?
A
- Labelled Line or Specificity Encoding: there are fibre tracts that are responsible for a specific taste sensation (e.g., there is a “salty” tract, or a “sweet” tract.)
- Cross-Fibre or Distributed Encoding: a taste sensation is the result of a pattern of activation of the different taste cells. Substances that cause similar patterns of activation will taste similar.
27
Q
what is the evidence for specificity coding?
A
- Mueller et al. (2005) used genetic cloning to determine if mice could be created that possessed a human receptor that responds to PTC, phenylthiocarbamide.
- Normally, mice do not have this receptor and do not respond to this substance.
- Only the mice with PTC receptors responded to PTC
28
Q
what is the evidence for distributed encoding?
A
- Figure on the right shows how 13 nerve fibers (A, B, C…) responded to 3 chemicals: ammonium chloride (NH4Cl ), potassium chloride (KCl) and sodium chloride (NaCl).
- The red and green lines show that the cross-fibre patterns for NH4Cl and KCl are similar.
- The pattern for sodium chloride (NaCl) indicated by the open circles is very different.
- Pattern coding predicts that NH4Cl and KC should taste similar, and NaCl dissimilar. - Erickson (1963) trained rats to avoid KCl.
- After training, when rats were presented with KCl, NH4Cl and Nacl. The results showed that:
- Rats avoided KCl, as expected
- Rats did not avoid NaCl, as expected
- Rats avoided NH4Cl because it tasted similar to KCl.
29
Q
what is tasta adaptation?
A
- Human saliva contains NaCl, but we do not normally experience a salty taste. This is because we have adapted to the concentration of salt in the saliva, so the sensation of saltiness has been ”lost” (like the sight of our noses in vision).
- If you rinsed your mouth with water, and tasted a solution with the same concentration of NaCl (denoted [NaCl]) as your saliva, you would taste the saltiness.
- Batoshuk et al. (1964) showed that when participants rinsed their mouths with water and were given solutions with different levels of NaCl, they would:
- When [NaCl] is high, taste saltiness
- When [NaCl] is low, taste bitterness
30
Q
what are the different tastes of salt?
A
- Dzendolet and Meiselman (1967) showed that:
- When [KCl] is low, participants tasted sweetness
- When [KCl] increases, sweetness is gradually replaced by saltiness.
- They suggest that this is because taste receptors have different absolute thresholds. In this case, sweet receptors have lower thresholds so will be activated by lower levels of salt.
- At higher [KCl] levels, the salt receptors become activate but also start inhibiting sweet receptors.
- Batoshuk et al. (1964)
- When [NaCl] is high, taste saltiness
- When [NaCl] is low, taste bitterness
- The concentration of different salts have different effects.
31
Q
what is the functional role of taste?
A
- Sweet tastes signal the presence of carbohydrates, an important source of energy.
- Umami, the taste of some amino acids, probably signals protein content.
- Bitter may signal presence of poisons (increased sensitivity during pregnancy; Nordin et al, 2004).
- Sour may signal dietary acids (in spoiled foods).
- Salt intake important in water balance.
- Activity in taste buds triggers digestive mechanisms.
32
Q
what is flavour?
A
- Combination of smell, taste, and other sensations (such as burning of hot peppers)
- Odour stimuli from food in the mouth reaches the olfactory mucosa through the retronasal route.
- The taste of most compounds is influenced by olfaction, but a few, such as MSG are not.
33
Q
what is the role of smell in taste?
A
- Hettinger, Myers, and Frank (1990)
- examined how people described the flavours of different compounds when they tasted them with nostrils clamped shut and with nostrils open.
- Each X represents the judgment of one person.
- There are significant differences between the two conditions. Smell plays an important role in taste.
34
Q
what role does flavour have in the brain?
A
- Rolls (2000) suggested that responses from taste and smell are first combined in the orbital frontal cortex (OFC), an area of the brain that mediates the reward component of tastes.
- O’Doherty et al. (2001) found that both pleasant (sweet) and aversive (salt) tastes activated adjacent areas of the OFC.
- OFC also receives input from the primary somatosensory cortex and the inferotemporal cortex in the visual what pathway.
35
Q
what is satiety and the orbital frontal cortex?
A
- Critchley and Rolls (1996)
- found that the responses of olfactory neurons to the smell of a satiating food were reduced compared to responses to the smell of non-satiated food in a selective manner.
36
Q
what are the bimodal olfactory neurons in the orbital frontal cortex?
A
- Critchley and Rolls (1996) also recorded bimodal taste/olfactory cells that are responsive to blackcurrant.
- These cells’ response to blackcurrant smell and taste were diminished after presentation of the blackcurrant smell or taste, respectively.
37
Q
what did Kringelbach et al. 2003 study?
A
- Kringelbach et al. (2003) measured ratings of pleasantness and OFC activity before and after a drink was consumed to statiety.
- Group A was given chocolate milk.
- Group B was given tomato soup.
- They reported that:
- Ratings and OFC activity declined for a consumed drink (chocolate milk for A and tomato soup for B).
- Ratings and OFC activity similar before and after satiety for a non-consumed drink (tomato soup for A and chocolate milk for B). - Activity in the OFC is determined by the reward component of the drinks and not their sensory quality.
38
Q
what are the factors that affect taste?
A
- Taste can be modulated by a variety of biological and environmental factors, including:
- Body mass index
- Smoking and alcohol consumption
- Aging
- Gender
- Exposure to pathogens
39
Q
what impact does negative emotional state have on taste?
A
- Dess and Edelheit (1998) found that after exposure to mild stressors, the participants experienced more intense bitter perception, as well as less intense sweet perception.
- Al’absi et al., (2012) reported that after exposure to acute stressors, participants rate umami and sweet solutions as less intense.
40
Q
what impact does mood have on taste perception?
A
- Noel and Dando (2015) recorded the taste intensity ratings and hedonic evaluations from approximately 550 attendees following men’s hockey games spanning the 2013–2014 season, a period encompassing 4 wins, 3 losses, and 1 tie.
- Their analyses revealed that positive emotions (with wins) correlated with enhanced sweet and diminished sour intensities, while negative emotions (with losses) associated with heightened sour and decreased sweet tastes.
41
Q
what impact does the use of condiments have?
A
- Brondelet al. (2009) evaluated the effect of renewal of sensory stimulations of previously eaten foods on sensory-specific satiety and intake. In their study, participants ate French fries then brownie cakes as much as they wanted in three conditions:
- Monotonous - fries then brownies were consumed alone
- Simultaneous - condiments (ketchup and mayonnaise for the fries, vanilla cream and whipped cream for the brownies) were added during intakes
- Successive - after intake of fries alone, ketchup then mayonnaise were available with fries and, after intake of brownies alone, vanilla cream then whipped cream were offered with brownies.
42
Q
what role does satiation have on taste?
A
- Tastes can promote appetite for certain foods, and can affect the motivation to continue or stop further food consumption.
- The quantities eaten in the Simultaneous and Successive conditions were significantly higher than those in the Monotonous one. They suggested that adding condiments and increasing food variety can increase food intake in the short term.
43
Q
what impact does eating disorders have on taste differences?
A
- Chao et al. (2019) conducted a systematic review on research assessing taste differences in patients with anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED).
- Psychophysical studies showed that individuals with BN, in general, had greater preference for sweetness than healthy controls, and those with AN had a greater aversion for fat than controls.
- In neuroimaging studies, findings suggested that predictable administration of sweet-taste stimuli was associated with reduced activation in taste-reward regions of the brain among individuals with AN but increased activation in BN and BED.
