Chemical Senses Flashcards
anosmia and effects
loss of sense of smell can result in a decrease in quality of life, decrease in motivation to eat, increase in risk of hazardous events (cannot smell fire, more food poisoning)
chemical senses
taste (molecules bind to receptors on tongue)
smell (moleculen bind to receptors in olfactory mucosa)
flavour (combination of taste and smell)
functions of taste and smell
detect and distinguish things that are important for survival and things that are bad for us
affective component: things that are good for us tend to taste/smell good
how often are taste receptors re-generated
every 1-2 weeks
how often are olfactory receptors regenerated
every 5-7 weeks
what is different about chemical senses vs. vision, hearing, touch
receptors are directly exposed to the environment and are easily damaged (so undergo neurogenesis)
basic tastes
salty (sodium chloride)
sweet (sucrose)
sour (hydrochloric acid)
bitter (quinine)
*umami (MSG)
which tastes are innate and why
sweetness is inherently rewarding - has high caloric/nutritive value = survival-based
bitterness is inherently rejected - associated with poisons (but this response can. be altered with habituation to foods like coffee, beer)
what are the types of papillae and where are they found?
filiform - all over the tongue (for texture detection, no taste buds)
fungiform - sides and tip
circumvallate - back to hold tastants before they are swallowed
foliate - back on sides to trap tastants
structure of the fungiform papillae
shaped like a mushroom with taste buds protruding
the taste bud has a taste pore where tastants bind (contains taste cells with nerve fibers)
taste cell has receptor sites for the four basic tastes - where transduction occurs
pathways to the brain from the tongue
chorda tympani nerve (front and sides of tongue)
glossopharyngeal nerve (from back of tongue)
superficial petrosal nerve (from soft palate)
vagus nerve (from mouth and throat)
pathway of tastants
to brain stem (nucleus of the solitary tract) - thalamus - frontal lobe (insula, frontal operculum, orbital frontal cortex)
population coding evidence for taste
recording from chorda tympani - 13 fibers responded in across-fiber patterns to produce perception of taste
specificity coding evidence for taste
giving mice a PTC-bitter receptor = avoid PTC
removing the bitter-Cyx receptor in mice = stop avoiding Cyx
giving rats amiloride (blocks sodium from entering receptors) lowers response from solitary tract neurons that respond to salty but not neurons that respond to salty-bitter combination
when do we use population and specificity coding for taste
population for subtle differences in tastes and specificity for basic tastes
evidence for individual differences and genetic impacts on taste
cats don’t have sweet receptors (lack a functional gene)
tasters can taste PTC, nontasters cannot (specialized receptors)
some people can taste PROP (higher densities of taste buds, specialized receptors)
tasters of PTC and PROP may be more sensitive to bitter substances (more avoidance)
microsmatic
weak sense of smell that is nonessential to survival
macrosmatic
well-developed sense of smell that is essential for survival
humans have 10 million receptors, dogs have 1 billion)
forced-choice method for detection threshold of smell
giving Ps one weak odourant and no odourant and they must choose which smells stronger
why are smells difficult to explain/classify
physical properties (chemical structure) don’t always relate to perception (similar structures can result in very different perceptions, and different structures can result in similar perceptions)
smells in our environment are combinations of molecules
steps for creating odour objects
perceptually organizing molecules into sources
1. analyzing in olfactory mucosa and bulb (transform into neural activity)
2. synthesizing into objects in the olfactory cortex (learning and memory)
pathway of smell
molecules - olfactory mucosa (olfactory receptors - electrical signals in olfactory receptor neurons) - olfactory bulb (glomeruli) - piriform cortex - orbitofrontal cortex, amygdala, hippocampus
*each olfactory receptor responds to a narrow range of odourants (we have 350-400) and each ORN contains one type of olfactory receptor
*1 type of ORN sends signals to 1-2 glomeruli = different patterns of activation
recognition profiles for odorants
patterns of activation in individual receptors (differences in recognition profiles account for differences in perception sweet vs. rancid)
chemotopic/odour/odotopic map
map of odorants in the olfactory bulb based on molecular features of odorants (not conserved in the piriform cortex, where activity becomes widespread)
formation of odour objects takes place in…
the piriform cortex by learning (creating neuronal connections which become recognized patterns of activity)
neurons in the PC can discriminate odour objects with exposure/training
Proust effect
taste and olfaction “unlock” memories (typically from childhood)
odour-evoked autobiographical memories
often from first 10 years of life, evoke strong emotions, associated with mental time travel (amygdala and hippocampus connections)
retronasal pathway
chemicals in food/drink reach the olfactory mucosa through the nasal pharynx
oral capture
sensations from olfaction and taste are perceived as from the mouth (tactile receptors)
orbitofrontal cortex neurons
has bimodal neurons (respond to more than one sense) which often respond to similar qualities
- for percetual representations of food and flavour
- expectation also affects flavour (cost of food, label, presentation of food)
sensory-specific satiety
after eating a particular food, odour of that food is perceived as less pleasant
reflected in the insula, amygdala, orbitofrontal cortex
correspondences
property of a chemical sense is associated with properties of other senses (with pitches, instruments, colours, textures)
influences
stimuli from one sense affect our perception of another sense (consonant music = sweeter chocolate, colour influences flavour, odour can have priming effects)
where do correspondences and influences come from
learning and associations, pleasure, emotions (lemon-yellow, bright colours = happiness = pleasant odours = pleasant feelings = soft fabrics)
developmental dimension of taste
mother’s food changes flavour of amniotic fluid = infant’s preferences
also the food she eats while breastfeeding and choice of first solid foods
