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2115 sensation & perception > Week 12 : Olfaction & taste > Flashcards

Week 12 : Olfaction & taste Flashcards

1
Q

chemical senses…

A
  • olfaction & taste derive their percepts from the chemical structures of molecules that come in contact with sensory cells lining the nasal cavity & tongue
  • olfaction (airborne) & gustation (in mouths)
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2
Q

The gatekeepers

A
  • our chemical senses play a crucial role in survival
  • the sensitivity of our chemical senses are highly informative in making decisions regarding how to interact with our environments
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3
Q

Odors…

A

the perceptual experiences that derive from the detection of odorants

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4
Q

Odorants

A
  • airborne chemical molecules
  • in order to be smelled it must float through the air
  • must be repellent to water
  • must be relatively small
  • but our olfactory system does not respond to al airborne chemicals (e.g. carbon monoxide)
  • sometimes air already contains odorant molecules & other times they can be forced through air (sniff)
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5
Q

many plants & animals emit molecules into air, some of which intended to be detected by…

A
  1. themselves (pheromones)
  2. other members of their species (mark territory/mate)
  3. other species (self-defence)
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6
Q

path… 1. nasal septum

A
  • wall of cartilage separating nostrils
  • damage causes deviated septum (interfere with breathing & smell)
  • damage can also be perforated/punctured septum (chronic cocaine use)
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7
Q
  1. turbinates
A
  • inside nasal cavity
  • function to disperse air
  • knots of tissue ensure air will be passed through the olfactory cleft & land on olfactory epithelium (transduction takes place)
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8
Q

Path after…

A
  • air passes thru cleft & rejoins air being sent through the pharynx toward the lungs
  • odorant’s from food find their way to the olfactory epithelium thru a passage in the oral cavity in the back of the mouth
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9
Q

Olfactory epithelium…

A
  • lines top of nasal cavity
  • projects to a small area at the base of the brain called olfactory bulb (above cribriform plate)
  • one at top of each nostril
  • die after about a month
  • have cilia extending into mucus coverage of olfactory epithelium & have transfusing elements on tips
  • 20 million cilia in human noses
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10
Q

transduction in the olfactory epithelium

A
  • different odor inducing molecules pass over the sensory epithelium & interact w/ olfactory receptor cells, with projections extending to the nasal cavity
  • each neuron is sensitive to a different odorant molecule (different smell)
  • this comes from the distribution of different odorant receptors at the endings of the neurones, each can only be stimulated by a particular odorant molecule
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11
Q

through cribriform plate…

A

-olfactory neurons then project through small holes in the cribriform plate & form glomeruli
- this bone separates the nose from the brain (susceptible to injury)

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12
Q

Glomeruli

A
  • they are localized spheres of synaptic endings that relay door signals to the mitral cells of the olfactory bulb (then to other brain structures)
  • the projections inside a glamorous come from olfactory receptors that respond to the same odorant…. so odor specificity is maintained in the mitral cells…
  • in the olfactory bulb
  • 2 types of glomeruli (mitral cells & tufted cells)
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13
Q

cells in the glomeruli form an odorant map… organizing similarly structured odorant’s together

A
  • odorants from chemicals with similar structures are processed adjacent to one another
  • but, odorants with similar chemical structures may not have similar subjective odors
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14
Q

The passages between the nasal cavity & olfactory bulb are so small…

A
  • the reason why smell may be adversely affected by head trauma
  • olfactory neurones undergo routine replacement through the lifespan by the basal cells, so the loss of sensory function is often temporary
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15
Q

Macrosomatic vs microsomatic

A
  • macrosmatic = species (bears, pigs & dogs) that depend heavily on smell
  • microsmatic = humans, who depend more on vision and audition (humans have only 350 olfactory receptor neurons out of the 1000)
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16
Q

Genes & olfaction

A
  • a collection of genes regulate the expression of different olfactory receptor neurons
  • there is a family of about 100 genes across mammalian species involves in genetic coding for olfactory transduction
  • in humans only 350 of these are active
  • this is a predictor of individual differences in olfaction in humans
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17
Q

Trigeminal nerve

A
  • many odorant’s may have a secondary sensory component described as a feeling
  • some burn (ammonia) and some sooth (menthol)
  • they cause reactions in the somatosensory system
  • this is from the trigeminal nerve that accounts for the mixing of senses
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18
Q

Idiosyncrasis of scent

A

it is very difficult to predict the sensation of smell that will be evoked by a chemical, even if its chemical structure is well known (e.g. musk vs no odorant’s is so similar)

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19
Q

Olfactory bulbs

A
  • structure & function of olfactory bulb/system differs across species
  • reflects the degree to which the sense of smell drives behaviour
  • e.g. humans have 6 million olfactory receptors 7 dogs have 50x that many
20
Q

Olfactory brain pathway

A
  • neurons of olfactory bulb travel along ventral surface of the brain via olfactory tract before slipping to a variety of brain regions
  • these brain regions include the hippocampus (memory) & amygdala (emotion) & areas that combine sensory system inputs
  • this generates more complete representations of our environment
21
Q

Principal olfactory pathway…

A
  • mitral cells that get input from olfactory sensory neurons (via glomeruli) project along the olfactory tract & target piriform cortex
  • that is the primary olfactory cortex
  • then, neurons target olfactory sensitive regions of thalamus & project to the orbitofrontal cortex (secondary olfactory Cortex)
22
Q

representations within the piriform cortex…

A
  1. anterior piriform cortex = front/associated with representing chemical structures of odorant’s & creates a map of odorants organized by chemical structure/ neurons narrowly tunes
  2. posterior piriform cortex = back/associated with odor’s quality, regardless of chemical composition (groups together odors that small similar)/ represents the subjective qualities of odor
23
Q

Amygdala & hippocampus

A
  • olfactory info has direct access to amygdala & hippocampus
  • this helps explain why doors elicit strong emotional reactions & others can evoke detailed memories
24
Q

Anosmia (smell blindnes)

A
  • inability to smell, usually caused by cribriform plate damage
  • damage can repair but may scar over
  • sinus infections can also cause this temporarily
25
Q

Olfactory detection

A
  • different odorants require different concentration for olfactory detection
  • the amount of odorant in the environment is measured as a function of the number of molecules of that odorant per 1 million molecules of air
26
Q

tip-of-the-nose phenomenon

A
  • occurs when a person is familiar with an odor but cannot recall its name, despite feeling as if he can
  • cuz… there is a commotion between olfaction, emotion & memory but a disconnect between olfaction & language
27
Q

Olfactory imagery

A
  • the ability to experience the ‘smell’ of a particular odor when it is not physical present
  • difficult for most ppl
  • ppl who have it showed brain activity in the piriform cortex when engaged in olfactory imagery
28
Q

Olfactory illusions

A
  1. olfactory environment that surrounds an odorant changes the way it is perceived
  2. verbal labelling can also cause olfactory illusions
  3. olfactory rivalry (switch back and forth between odors being presented to each nostril, not at same time)
29
Q

Tastants, taste & flavour

A
  • tastants = we respond to tastant molecules that dissolve when in contact w/ our saliva & initiate a transduction response
  • taste = perception of the transduction of tastants
  • flavour = combined sensory experience of a food (trigeminal nerve)
30
Q

5 basic tastes

A

these tastes stimulate different taste sensitive receptors on the tongue in separable areas…
1. salty
2. sweet
3. sour
4. bitter
5. umami

31
Q

Tongue

A

principle taste organ

32
Q

Surface of the tongue is covered with papillae of 4 different types…

A
  1. circumvallate (pimple) papillae - back of tongue in a roe
  2. foliate (ridged) papillae - side of tongue
  3. fungiform (mushroom) papillae - edges & top of tongue
  4. Filiform papillae - all over (somatosensory receptors)
33
Q

Filiform papillae

A
  • the most numerous subtype, cover the broadest region of the tongue
  • they do not contain tastebuds
  • instead, they are touch sensitive & communicate info related to the texture of food & pressure placed on the tongue during eating/articulation`
34
Q

1-3 papillae

A
  • they have the taste buds
  • each papillae has several hundred taste buds
  • each taste bud has between 50-150 taste receptors
35
Q

taste buds

A
  • 10,000 in human mouths
  • each have several taste cells, whose ends are exposed via a pore at the surface of the tongue
  • on the endings of taste cells, we see receptor channels (cilia) sensitive to chemical compounds related to the sensations of test
  • when activated, initiate signals that result in taste
36
Q

The sensory epithelium undergoes frequent damage (burning, etc.)…

A
  • thankfully, sensory neurons that are the taste buds are continuously replaced so the damage rarely results in lasting inability to taste
  • epithelial progenitor cells surround the taste cells & can grow into any of the surrounding cell types to replace damages/aged cells
37
Q

Not all tongues are created equally… (2)

A
  1. non tasters = have a very low density of papillae on the surface of their tongue
  2. supertasters = have very densely packed papillae… the papillae of super tasters tongues have been shown to have greater inner interaction by somatosensory nerves… suggesting they also have heightened awareness of textural cues
38
Q

what do non- & super-tasters tell us?

A
  • these differences might help explain behavioural differences in taste sensation
39
Q

Taste pathway in the brain… the taste sensitive neurons project to the brain along 3 cranial nerves…

A
  1. 7th (cortatympani) cranial nerve = contacts receptors along the front 2/3 of the tongue
  2. 9th (glossopharyngeal) cranial nerve = contacts receptors along the back 1/3 of the tongue
  3. 10th (vagus) cranial nerve = projects to the based of the tongue & epiglottis where it plays a minor role in taste sensation
40
Q

all 3 cranial nerves project to…

A
  • the nucleus of the solitary tract (in medulla)
  • which projects to the ventral pestero medial nucleus of the thalamus
  • finally, taste info is send to the primary taste cortex, which comprises the anterior insula and frontal operculum
41
Q

not a ton is known about the organization of the primary taste cortex, but…

A
  • it is clear that taste info is combined with cues from vision & smell to make determinations surrounding food quality
  • there are close times between taste sensitive regions of the brain & those whose encode emotion & pleasure
42
Q

Taste has a variety of cues that can be derived at the level of taste buds…

A
  1. onset/aftertaste
  2. intensity
  3. quality (5 tastes)
  4. hedonic (pleasant/unpleasant)
  5. localization
43
Q

flavour is composed of…

A
  1. hunger/thirst
  2. vision
  3. audition
  4. taste
  5. ‘mouth feel’
  6. SMELL !!
  7. our own internal state
44
Q

Where does flavour reside in the brain?

A
  • info from across senses coverage on the orbitofrontal cortex to inform flavour perception
  • this region is known to play a role in encoding affective value (emotions) & computing from these emotions, the value we perceive a stimulus to have
45
Q

interaction between smell & taste

A
  • the most influential component of flavour
  • oral & nasal cavities are connected & give rise to the ability to smell foods that are being eaten
  • the passage of olfactory molecules via the throat is celled retro nasal olfaction & is a prominent part of his-end wine tasting

2115 sensation & perception (14 decks)

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