NEU 325 - For Final Exam Flashcards
(62 cards)
1
Q
Olfaction
A
The sense of smell
2
Q
Odor vs. Odorants
A
Odor: a general smell sensation of a particular quality
Odorants:
- chemical compounds
- but not every chemical is an odorant
- most are small, volatile, and hydrophobic (don’t diffuse in water)
3
Q
Is smell even relevant to humans?
A
- our machinery is less sensitive than other animals (dogs, etc)
- dogs can detect odorant concentrations 100x lower than humans (dogs: can detect 1 part-per-million, humans: 100 parts-per-million)
- but, experiments show that human receptors respond to single odorant molecules
- the difference? dogs have ~1 billion, humans have ~10 million
4
Q
Can humans scent track?
A
Theoretically possible – humans can use info from both nostrils for scent tracking
- two nostrils sample different regions of space, and humans use both nostrils for scent tracking
5
Q
how good is our sense of smell?
A
- latest findings suggest that we can detect over 1 trillion smells
- we can only detect about 7.5 million colors
6
Q
Olfactory cleft
A
space at the back of the nose into which air flows, where the main olfactory epithelium is located
7
Q
Olfactory epithelium
A
secretory mucosa whose primary function is to detect odorants
- the ‘retina’ of the nose
- 3 cell types:
1. supporting cells
2. basal cells
3. olfactory sensory neurons (OSNs)
8
Q
What are supporting cells?
A
- in the olfactory epithelium
- provides metabolic and physical support for the olfactory sensory neurons
9
Q
What are basal cells?
A
- in the olfactory epithelium
- precursor cells to the olfactory sensory neurons
10
Q
What are olfactory sensory neurons
A
- in the olfactory epithelium
- main cell type in the olfactory epithelium
- make direct contact with the physical stimulus
- responses are slow
- OSN axons are the thinnest and slowest in the body
- short life span: die and are regenerated every ~6 weeks
11
Q
Cilia in the olfactory epithelium
A
- Cilia are hairlike protrusions on the OSN dendrites
- have receptor sites for odorant molecules
- structures for olfactory signal transduction
12
Q
olfactory receptor in the olfactory epithelium
A
- olfactory receptor: region on the cilia of OSNs where odorant molecules bind
- takes 7 or 8 odor molecules binding to a receptor to initiate an action potential
13
Q
What is the cribriform plate
A
bony structure with tiny holes (even with the eyebrows), separating the nose from the brain
- axons from OSNs pass through tiny holes to enter the brain
14
Q
what are mitral cells
A
the main projective output neurons in the olfactory bulb, in the olfactory epithelium
15
Q
What are glomeruli
A
in the olfactory epithelium - spherical conglomerates containing the incoming axons of the OSNs
- each OSN converges on two glomeruli
16
Q
what is the sensory pathway for the olfactory system?
A
odorant molecule gets picked up by the receptors, then olfactory cilia, then olfactory sensory neuron, then through the cribriform plate, to the glomerulus, to the mitral cels, then off to olfactory cortex and other brain structures
17
Q
olfactory bulb
A
the blueberry-sized extension of the brain just above the nose, where olfactory information is first processed
- there are two olfactory bulbs, one in each brain hemisphere, corresponding to the left and right nostrils
18
Q
primary olfactory cortex
A
cortical area where olfactory information is processed
19
Q
limbic system
A
- involved in many aspects of emotion and memory
- olfaction is unique for its direct connection to the limbic system
20
Q
Why is olfaction weird?
A
- direct connection to cortex
- many subsequent cortical connections to the midbrain
- also, no ‘smell-o-topic’ maps: no topography (that we know of)
21
Q
Anosmia
A
The total inability to smell, most often resulting from sinus illness or head trauma
- a hard blow to the front of the head can cause the cribriform plate to be jarred back or fractured, slicing off the fragile olfactory neurons
- anosmia causes a profound loss of taste as well as smell
22
Q
What is the genetic basis of olfactory receptors
A
- genome contains about 1000 different olfactory receptor genes; each codes or a single type of OR
- all mammals have pretty much the same 1000 genes
- however, some genes are non-functional ‘pseudogenes’
- dogs & mice: about 20% are pseudogenes
- humans: between 60-70% are pseudogenes
- each person has a different number of pseudogenes, resulting in individual differences in sensitivity to smells
23
Q
What is the trigeminal nerve’s role in the perception of odors?
A
carries pain and temperature information from mouth and nose
24
Q
Shape-pattern theory of olfactory perception
A
- scent percept depends on fit between olfactory receptor shape and odorant shape - the binding pattern of odorants in the olfactory epithelium produces specific firing patterns of neurons in the olfactory bulb, which then determine the particular scent we perceive
- now dominant theory
25
Vibration theory
- now defunct
- proposes that every perceived smell has a different vibrational frequency, and that molecules that produce the same vibrational frequencies will smell the same
26
Study of stereoisomers
- molecules that are mirror-image rotations of one another; although they contain the same atoms, they can smell completely different
- vibration theory cannot explain this phenomenon
27
How do olfactory receptors work their activation timing and order?
- different odorants activate the same receptors with different timing
- explains how we can detect far more odorants than number of olfactory receptors
28
Why do we have two nostrils?
- airflow is greater into one nostril than the other, due to the slight swelling that obstructs airflow
- switches nostrils every 4-6 hours
- odorants sorb across nasal mucosa at different rates
- odorants do smell different in nostrils, depending on the airflow and the sorption of the odorant
29
high-sorption odorant
- induces small response when airflow is low, and a large response when airflow is high
30
low-sorption odorant
- large response when airflow is high, and small response when airflow is small
31
how much stimulation is required before we perceive a smell
- olfactory detection thresholds: depend on several factors
- women: generally lower thresholds than men, especially during ovulatory period of menstrual cycles (but sensitivity is NOT heightened during pregnancy)
- professional perfumers and wine tasters can distinguish up to 100,000 odors
32
does our ability to smell ever change?
yes - by 85, 50% of population is basically anosmic
- like those high-frequency sine waves, enjoy smelling while you can
33
Odor hedonics
the 'liking' dimension of odor perception
- measured with scales of pleasantness, familiarity, and intensity
34
Pleasantness, familiarity, and intensity
Pleasantness: obvious
Familiarity: tend to like odors we have smelled before
Intensity: more complicated relationship with odor liking
35
Olfactory Hedonics, NATURE v NURTURE?
- verdict: almost completely nurture
- infants are not put off by sweat or feces, don't discriminate banana from smell of rancid food
- cross-cultural data supports associative learning
Wintergreen study
- Americans like it, English rated it the most unpleasant of many odors
US army tried to develop a stink bomb for crowd dispersal, but couldn't find a smell that was universally disgusting
36
What is the evolutionary argument for olfactory hedonics
- generalists (like us and roaches) don't need innate smell aversions to predators
- learned taste aversion: avoidance of a flavor after it has been paired with gastric illness
- found it has to do with the smell and not the taste
37
What are the two caveats for the theory that odor hedonics are mostly learned?
- (trigeminally) irritating odors may elicit pain responses, which all humans have an innate drive to avoid
- potential variability in receptor genes and pseudogenes that are expressed across individuals
38
Are odors really the best cue to memories?
- memories triggered by odor cues are distinctive in their emotionality
- but not (as it turns out) more accurate
39
Taste vs. flavor
Taste = sensation from tongue and mouth
Flavor = combination of pure taste and smell ("retronasal olfaction")
40
What happens when we can't perceive taste but CAN perceive smell?
- patient case: damaged taste but normal olfaction -- could smell lasagna, but reported that it had no flavor
- conclusion: brain blocks olfactory contribution to taste, unless taste receptors report something
41
Taste & Olfaction work ____ to create flavor
together
42
what are the two options to enhance flavor?
1. add sugar
2. add 'volatile' molecules (to intensify retronasal olfaction) -- very recently discovered
43
what are volatile molecules
- different volatiles can have different sensory effects -- enhance saltiness or decrease bitterness
44
What was the heirloom tomato study?
- there were 80 types of heirloom tomatoes
- identified genes that enhance sweetness without increasing sugar
- increasing volatile molecules detected via olfaction
- created the garden gem tomato, which had the stability + yield of grocery store tomato, and the volatiles of heirloom tomatoes
RESULT: tastes much better than grocery store, nearly as good as heirloom
45
What was the chocolate study?
- plug nose
- chew chocolate and notice sensation (sweet with a hint of bitter)
- swallow & release nose: volatile molecules will immediately flow up behind palate and into the nasal cavity, releasing full flavor of chocolate
46
papillae
- gives the tongue its bumpy appearance
- taste papillae (circumvallate, foliate, and fungiform) all contain taste buds
- no subjective awareness of location in the mouth
47
What is the genetic variation in taste experience?
- supertasters: have high density of fungiform papillae (perceive the most intense taste sensations)
- # of buds varies enormously -- 3,000 to 12,000 per tongue (4x more)
- such high variation is unique to the senses
48
What does each taste bud consist of?
- taste receptor, taste pore, and microvilli
49
What are the two mechanisms for taste transduction?
1. Small charged particles or ions (salty and sour) — enter ion channels in microvilli
2. Molecules bind to receptor (sweet and bitter) — ‘lock and key mechanism’ similar to receptors in the olfactory system
50
What is Edwin Boring’s model?
- bogus
- model that proposed that each taste bud can detect multiple kinds of tasting
- coding depends on concentration of different receptors
51
What are the four basic tastes?
Ions enter the cell
- salty
- sour
Tastant binds to receptor on cell
- sweet
- bitter
52
Salty Taste
- made up of two charged particles (cation (+) and anion (-))
- ability to perceive salt is not static — low-sodium diets will increase intensity of salty foods
- liking for saltiness is not static — early experiences can modify salt preference (chloride-deficiency in childhood leads to increased preference for salty foods later)
- gestational experiences may affect liking for saltiness
- survival value: body needs sodium to survive
53
Sour Taste
- comes from acidic substances
- survival value: at high concentrations, acids will damage both external and internal body tissues
54
Sweet Taste
- evoked by sugars
- many different sugars that taste sweet
- glucose: principle source of energy for most animals
- sucrose: common table sugar. Combination of glucose and fructose (sweeter)
55
How can you explain differences in sweetness of different sweeteners?
- single receptor responsible for all sweet perception
- could be activation of other receptors (i.e. bitter) OR different binding to the receptor itself
56
What do artificial sweeteners do?
- synthesized molecules that bind to the same receptor
- saccharine - discovered in 1879 by Ira Remsen, researcher worked on coal tar and noticed his hands ‘tasted sweet’ after work
- unclear whether it actually helps with weight loss
57
Bitter Taste
- 1000 different bitter molecules (many from plants that use them for protection)
- 25 different bitter receptors
- quinine - prototypical bitter substance (sugar is added to tonic water to cancel out the bitter taste; has the same sugar content as soda)
- bitter sensitivity is affected by hormone levels in women, intensifies during pregnancy
- in general, we do not notice the difference between bitter-tasting compounds; we simply avoid them
58
What is genetic variation in taste experience?
- Fox (1931) discovered that PTC tastes dramatically different to different people
- bitter taste to some but not to others
- 1960s: started using PROP instead of PTC
Genes for PROP receptors discovered in 2003
- individuals with two recessive genes are nontasters of PTC/PROP
- individuals with one or more of the genes are tasters of PTC/PROP
59
What is special about PROP supertasters?
- high density of fungiform papillae AND very intense sensation of PROP
60
PROP taster experiment
cross-modality matching
- nontasters - the sound of a watch or whisper
- medium tasters - the smell of frying bacon, or the pain of a mild headache
- supertasters - the brightness of the sun, or the most intense pain ever experienced
61
cross-modality matching
method for comparing intensity of sensations across different sensory modalities
62
Umami
5th basic taste?
- comes from monosodium glutamate, identified by Japanese chemists in 1900s
- glutamate: importnat neurotransmitter
- claim to be the 5th basic taste, came from MSG manufacturers (marked as a flavor enhancer)
- controversial: not perceptible in many foods; not a 'basic taste' bc not everyone reacts in the same way
- may bind to receptor in gut (soup with MSG preferred if eaten, but not if merely held in the mouth)
