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Biology 404 > Olfaction > Flashcards

Olfaction Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are the very general stages of perception in sensory systems?

A

Receptor activation > Detection > Transduction > Encoding of info > Conscious perception

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2
Q

What are the 3 chemical senses?

A

Taste
Smell
Detection of pheromones

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3
Q

What are the 2 olfactory pathways in mammals (maybe in humans, maybe not…)

A

Accessory olfactory pathway (Vomeronasal pathway) and main olfactory pathway

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4
Q

True or false: the VNO and MOE pathways are distinct units

A

False: there is a lot of overlap between the 2 pathways

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5
Q

Describe the human main olfactory bulb

A

It is much smaller than other mammal olfactory bulbs

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6
Q

Describe the very general pathway of the mammalian/human main olfactory system

A

Sensory cells in the main olfactory epithelium project through the cribiform plate to the main olfactory bulb, where they synapse to glomeruli, then in the glomerulus synapse to mitral cells, signals are then transmitted to higher processing areas of the brain

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7
Q

True or false: an single odour is produced by the perception of a discrete chemical compound

A

False: an odour = a plume of many different odorant compounds

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8
Q

Describe the chemical properties of an effective odorant

A

Should be a small molecule which is volatile

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9
Q

Odorants can be grouped these 2 ways

A

By chemical structure/type and by concentration

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10
Q

What are 4 requirements of the olfactory system?

A
  1. Sensitivity (discriminate between strengths)
  2. Integration (e.g. odorant plume)
  3. Discrimination (perception and identification of different odorants)
  4. Memory of different odorants
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11
Q

The sensory neurons from the MOE project to…

A

The main olfactory bulb (MOB)

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12
Q

The synapse between cells in the MOE to the MOB occurs in…

A

The glomeruli

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13
Q

Where are glomeruli located?

A

In the olfactory bulb

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14
Q

In the rodent olfactory system, where are the olfactory receptors located? (where in the cell)

A

On the cilia of the olfactory neurons of the MOE

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15
Q

The “relay centres” of the olfactory system are the…

A

Glomeruli

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16
Q

Define anosmia

A

Loss of smell

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17
Q

More common than complete anosmia is..

A

Partial anosmia, the loss of certain smells

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18
Q

Partial anosmia may be an indicator of these diseases (2)

A

Parkinson’s and Alzheimer’s

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19
Q

Partial anosmias are common with these kinds of odors

A

Musk odors

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20
Q

Normal, gradual loss of smell as a person ages is associated with a decrease in…

A

Apetite

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21
Q

In some COVID patients whose smell does not return, what is the cause of this anosmia?

A

Loss of supporting olfactory cells (“supporting cells”) which normally help nourish and support OSNs

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21
Q

In some COVID patients whose smell does not return, what is the cause of this anosmia?

A

Loss of supporting olfactory cells (“supporting cells”) which normally help nourish and support OSNs

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22
Q

True or false: the olfactory system transmits information via action potentials

A

True

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23
Q

What kind of neurons are OSNs based on the structure classifications of neurons (unipolar/bipolar/multipolar)

A

Bipolar

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24
Q

Who were the 2 scientists who shared the Nobel prize for the identification of olfactory receptors

A

Buck and Axel

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25
Q

What were the 3 hypotheses about olfactory receptors that Buck and Axel had?

A
  1. GPCRs
  2. Receptor gene family must be large and diverse
  3. Expression of receptors will be restricted to the olfactory epithelium
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26
Q

How did Buck and Axel go about trying to find olfactory receptors?

A

Designed a primer for a TM region of a GPCR which is common to many GPCRs and used RT-PCR on the MOE

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27
Q

If all GPCRs are roughly the same length, how did Axel and Buck design a system which would be able to indicate if they had found a multigene family?

A

Added Hinf1: cuts at a specific sequence common in GPCRs

First column: Hinf1 Fragments add up to 700 bp

2nd column: Hinf1 fragments add up to wayyy more than 700 bp: probably found a multigene family!

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28
Q

In olfactory neurons, how many kinds of olfactory receptors are present?

A

In general: one receptor type per neuron!

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29
Q

If olfactory receptors had not been GPCRs, would Axel and Buck have been successful in their experimental design? Why not?

A

No, because they were looking for a highly conserved region of GPCRs, and other types of receptors don’t necessarily share structural homology the same way GPCRs do

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30
Q

Are olfactory receptors exclusive to the main olfactory epithelium?

A

Mostly in the olfactory system but they exist outside of this also

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31
Q

Which of Axel and Buck’s original 3 hypotheses about olfactory receptors turned out not to be entirely true?

A

Olfactory receptors are only in the olfactory system: some are elsewhere

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32
Q

What receptor families of olfactory receptors are present in the vomeronasal system?

A

V1Rs and V2Rs

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33
Q

What are the 5 classes of olfactory receptors?

A
  1. Olfactory receptors (in the MOE)
  2. V1Rs (VNO)
  3. V2Rs (VNO)
  4. Trace amine-associated receptors (TAARS, MOE)
  5. Formyl peptide receptors
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34
Q

Describe combinatorial coding in olfactory receptors

A

An odorant activates a particular set of olfactory receptors: this encodes a distinct signal for each odor

35
Q

What is the advantage of combinatorial coding?

A

Uses fewer receptors to get more specificity

36
Q

In olfactory receptors, a single receptor recognizes (single/multiple) odorants

A

Multiple

37
Q

In olfactory receptors, a single odorant is recognized by (single/multiple) receptors

A

Multiple

38
Q

After the synapse at the glomerulus, the main output neuron of olfactory information is…

A

Mitral cells

39
Q

What are the key interneurons of the olfactory system?

A

Periglomerular cells and granule cells

40
Q

The periglomerular and granule cells are analogous to these cells in the visual system

A

Horizontal and amacrine cells

41
Q

Describe the organization of the MOE and MOB

A

There is zone to zone projection: receptors
are organized into zones of glomeruli which respond to similar stimuli

42
Q

What is the average life span of OSNs?

A

30-60 days

43
Q

Are OSNs replaced throughout life, or post-mitotic?

A

Replaced throughout life

44
Q

The stem cells which replace OSNs are called…

A

Basal cells

45
Q

Axons of like OSNs terminate in…

A

The same glomerulus

46
Q

The more abundant kind of interneuron in the olfactory system is the…

A

Granule cell

47
Q

Describe why the glomeruli are the signal processing centers of the olfactory system

A

Synapse happens there, input from interneurons (lateral inhibition) happens at glomerulus

48
Q

True or false: glomeruli participate in cross-talk to modify signals

A

True

49
Q

Where are the 2 zones of neurogenesis in the adult brain?

A
  1. Subventricular zone of the lateral ventricles
  2. Subgranular zone of the dentate gyrus

Both in the hippocampus!

50
Q

Cells born in the subventricular zone migrate (directionally) to this area of the brain

A

Rostrally to the olfactory bulb

51
Q

Describe birth dating of olfactory neurons

A

Inject BrdU into cells and detect using BrdU sensitive antibody

BrdU labels cells in S-phase

Can observe where they migrate into the brain

52
Q

When a nare was blocked (sensory deprivation), how did the number of BrdU-positive cells change compared to the unblocked nare of a mouse?

A

Fewer BrdU-positive cells in the blocked nare: sensory input increases OSN production

53
Q

Similar molecules tend to activate glomeruli which are…

A

Near each other

54
Q

What kind of synapses occur in the olfactory system which is uncommon elsewhere in the nervous system

A

Dendrodendritic synapses

55
Q

Dendrodendritic synapses in the olfactory system occur between these cell types

A

Mitral and granule cells

56
Q

GABA acts on these channels in mitral cells, opening them and causing this result

A

Cl- channels, causing influx of chloride causing hyperpolarization: this inhibits firing of neighbouring cells to increase acuity

57
Q

In a study by Sousy et al (2009), SpH mice (fluorescent pH-sensitive imaging tool) were examined. What were the main findings? (2)

A
  1. Glomeruli map which react to similar odorants are reliably placed across animals
  2. There is a local diversity in sensory tuning
58
Q

Cells which have different classes of olfactory receptors also differ in this way

A

Have unique transcriptomes! Cells clearly reacting in response to odorants in unique ways

59
Q

Each OSN having a unique transcriptome may be useful for this developmental process

A

Axon pathfinding

60
Q

What are the final destinations for the newborn cells of the SVZ?

A

Will become granule and periglomerular cells

61
Q

Do granule and periglomerular cells express olfactory receptors?

A

No

62
Q

How does an increase in granule cells affect olfactory discrimination of highly similar odorants?

A

Granule cells synapse between mitral cells (lateral inhibition)

When there are more granule cells, neighbouring mitral cells are more silenced when a central granule cell is active: better acuity

63
Q

What are the 2 lesser-known branches of the olfactory system

A

The gruenberg ganglion and the septal organ of masera

64
Q

What are the 2 classes of pheromone signals discussed in this course

A

Primers and releasers

65
Q

V1Rs use this kind of G protein

A

Galpha i2

66
Q

V2Rs use this kind of G protein

A

Galpha o

67
Q

How many V1R receptors have been found in humans?

A

5

68
Q

How many V2R receptors have been found in humans?

A

None

69
Q

Where are human V1Rs expressed?

A

In the MOE

70
Q

In mice, (V1R/V2Rs) are closer to the lumen

A

V1Rs closer to lumen

71
Q

The first ligand to be indentified for the VNO neurons was…

A

2-heptanone

72
Q

Do humans have a VNO?

A

No

73
Q

V2R are coexpressed with these molecules

A

MHC class Ib

74
Q

The proposed reason why V2Rs and MHC molecules are coexpressed is…

Why do we think this?

A

MHC might bind different immune-related ligands and aid in signalling of V2Rs in some way

Think this because MHC are expressed in dendritic tips

75
Q

Which MHC receptors have been located near the dendritic tips of VNO olfactory neurons

A

M1 and M10 - think they have a role in the detection of pheromones

76
Q

What is the one difference in the signal transduction cascade between V1Rs and V2Rs?

A

Use different G-proteins
V1R: Gai2
V2R: Gao

77
Q

Describe the general projections of the cells in the VNO

A
  1. VNO neurons project to AOB glomeruli
  2. In glomerulus, neurons synapse to mitral cells
  3. Mitral cells project to the vomeronasal amygdala
78
Q

Describe the ordering of glomeruli in the AOS

A

Not quite as ordered as the main olfactory system

79
Q

Describe the projection organ to organ of the vomeronasal system

A

VNO > AOB > Amygdala > Hypothalamus

80
Q

Describe the projection organ to organ of the main olfactory system

A

MOE > MOB > Piriform cortex + friends > Thalamus

81
Q

Other than the piriform cortex, the MOB also makes some connections to…

A

The amygdala

82
Q

Other than the thalamus, the piriform cortex also makes projections to…

A

The hypothalamus

83
Q

What of the 5 tastes are aversive?

A

Sour, salty, and bitter

84
Q

What is the key nutrient being detected by “sour” neurons

A

Protons (H+)

85
Q

True or false: the tongue has an intrinsic taste map

A

False

86
Q

Name the different coloured areas of papillae

A

Red: Circumvallate papilla (singular!)
Green: Foliate papillae
Purple: Fungiform papillae

Biology 404 (14 decks)

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