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BIOL 404 FINAL > Olfaction > Flashcards

Olfaction Flashcards

1
Q

olfaction deals with sensing _____

A

chemical energy

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2
Q

biological functions of olfaction

A

survival, communication

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3
Q

explain the function of survival

A

finding food, food selection -> olfaction can provide information about nutritional benefits, navigation, predator avoidance

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4
Q

explain the function for communication

A
  • Recognition of members/non-members of a social group -> Via the vomeronasal system.
  • Mother/infant bond (attachment)
  • identification of territory
  • Mating/reproduction
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5
Q

what is the main olfactory epithelium (MOE) lined by?

A

mucus and odorant binding proteins

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6
Q

What is the role of mucus in the olfactory epithelium?

A

It functions in protection and holding odorants close to receptors.

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7
Q

where is mucus produced?

A

by bowmans glands and is located under the basal lamina of the membrane

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8
Q

Where do odorant binding proteins reside, and what is their function?

A

reside within the mucus. Their function is to bind odorants.

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9
Q

Where do Olfactory Receptor Neurons (ORNs) reside?

A

in the olfactory epithelium

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10
Q

Describe the structure of olfactory fila and their projection.

A

~20 axons bundle up to form each olfactory fila. They project through the cribriform plate and make their way to the olfactory bulb.

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11
Q

What distinguishes olfactory axons in terms of thickness and myelination?

A

are among the thinnest in our brain, and they are unmyelinated, conducting very slowly.

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12
Q

Approximately how many odorants can we distinguish?

A

approximately 5000 odorants.

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13
Q

Where is the Main Olfactory Epithelium (MOE) located?

A

at the top of the nasal cavity.

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14
Q

Why do we sniff, and what is its connection to the MOE?

A

Sniffing directs air to the top of the nasal cavity, where the MOE is located.

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15
Q

stimualtion of the olfactory nerves result in

A

smell

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16
Q

stimulation of the trigeminal nerve (cranial nerve V) tells us

A

there is something dangerous/irritating in the environment

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17
Q

label this diagram:

A

a: receptor cell axons
b: basal cell
c: dividing stem cell
d: developing receptor cell
e: olfactory knob
f: olfactory cilia
g: odorants
h: mucus
i: supporting cell
j: mature receptor cell
k: bowmans gland
l: cribriform plate

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18
Q

most neurons are not able to regenerate, can olfactory neurons?

A

yes, regen monthly. this is due to being exposed to the environment

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19
Q

T/F: regeneration may be impaired after COVID

A

true, leads to olfactory deficits

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20
Q

odorant perception is more emphasized in other mammals due to

A

the variation in the types and numbers of ORNs different species have

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21
Q

dogs and olfaction

A

can have up to a billion ORNs, which line the whole nasal passage to increase sensitivity. Also have a larger olfactory bulb than humans.

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22
Q

odorant perception depends greatly on what?

A

the concentration of the odorant

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23
Q

what can concentration of an odorant affect?

A

whether an odorant is detected or not and also how we perceive it

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24
Q

enantiomers can also produce….

A

different perceptions of odorants

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25
Q

where are receptor potentials generated in receptor neurons?

A

in the cilia of receptor neurons

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26
Q

Why is the patch clamp experiment crucial in olfactory research?

A

provides a quantitative response, allowing observation of the strength of the conductance. Without patch clamping, only a spike without quantitative attributes would be observed.

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27
Q

How does mucus contribute to olfactory perception?

A

bathes cilia, contains odorants and odorant-binding proteins (OBPs), enabling humans to detect and perceive odors even at small concentrations, down to a few parts per billion.

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28
Q

olfactory receptors are _____, with a G-protein alpha subunit called _____

A

GPCRs, Golf

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29
Q

what happens upon G-protein activation?

A

the alpha subunit Golf dissociates and activates adenylyl cyclase, which catalyzes the conversion of ATP to cAMP.

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30
Q

what does heightened concentration of cAMP do?

A

activates a cAMP-gated Na+/Ca+ ion channel (a CNG channel), allowing Ca2+ and Na+ to flow into the cell.

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31
Q

what does Ca2+ activate?

A

a Ca2+-gated Cl- channel, resulting in an efflux of Cl- (calcium-activated Cl- current).

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32
Q

what is the reverse potential for chloride in normal neurons?

A

around -80

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33
Q

what is the reversal potential for ORNs?

A

closer to 0 mV so Cl- efflux causes depolarization

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34
Q

what is this current inhibited by?

A

NFA

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35
Q

the Ca2+ gated channel in ORN cillia is …

A

ANO2

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36
Q

what else does Ca2+ activate?

A

a Na+/Ca2+ exchanger, which inputs 3-4 Na+s for every output of 1 Ca2+

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37
Q

what is depolarization of ORNs mediated by?

A

1) cyclic nucleotide-gated channels (CNG), 2) Cl- efflux, and 3) the Na+/Ca2+ exchanger.

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38
Q

what does NKCC1 transport?

A

transports Na+, K+, and 2Cl- into the cell.

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39
Q

NKCC1 is much more _____ in ORNs, which results in its high intracellular Cl- concentration at _____

A

abundant, resting potential

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40
Q

this results in ____ and ______ being excitatory, as opening ___ and ____ channels Cl- moves out of the cell

A

GABA, glycine

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41
Q

what is ANo2

A
  • A cilial calcium-activated chloride channel that mediates olfactory amplification.
  • Expressed highly in the MOE
42
Q

if ca2+ is caged….

A

there is a large cl- current seen upon liberation in the patch clamp experiments, where voltage is held at the reversal potential for cl- (0mv)

43
Q

is this seen in ANO2 KOs?

A

no

44
Q

does knocking out CACl channels effect a mouses ability to detect odors?

A

it had no effect in go/no-go tasks

45
Q

what does go/no-go tasks entail?

A

involves rewards/punishments based on licking behavior in the presence of absense of odors

46
Q

what happens if the mouse licks in presence of odor?

A

if mouse licks, gets a reward

47
Q

what happens if mouse doesnt lick and when there is no odor

A

if mouse doesnt lick, gets a reward

48
Q

what happens if odor present and mouse doesnt lick?

A

doesnt get reward

49
Q

what happens if mouse licks and there is no odor?

A

doesnt get reward

50
Q

ANO2 KOs didnt show an impairment in _____

A

perceiving a stimulus

51
Q

what did ANO2 KOs make researchers believe?

A

that while ANO2 amplifies the current, the current still exists without it and mice can detect small signals.

52
Q

what did another experiment showing ANO2 KO mice show?

A

required longer times to identify new odorants, which is an innate behaviour. However, this can be overcome with time.

53
Q

we are able to detect many ____ in the environment because we have _____ distributed in the ______

A

odorants, millions of olfactory receptors, olfactory epithelium

54
Q

ORs are their own gene family with a….

A

highly conserved G-protein sequence

55
Q

T/F: expression of ORs are not restricted to the MOE

A

false, they are restricted to the MOE

56
Q

how did researchers identify this gene family?

A

designed primers to anneal to conserved regions (a 700 bp region of the theorized receptor).

57
Q

they used ____ prepared via _____ from olfactory epithelium RNA, and used PCR to ____ this DNA with a series of different primers

A

cDNA, reverse transcription, amplify

58
Q

once cDNA was made, a _____ was made to chew up the remaining RNA

A

restriction endonuclease

59
Q

when did they see when running PCR results?

A

saw multiple bands and concluded that there was a multigene family of G-protein coupled receptors that encode for the OR

60
Q

ORs are expressed on the ____ of ORNs

A

cillia

61
Q

each ORN only expresses ____ type of OR

A

one

62
Q

there are _____ ORNs of each type of OR

A

~10,000

63
Q

is there a specified distribution of ORN types?

A

yes, across the nasal concha of the nasal cavity

64
Q

odor perception is the result of the activation of _______

A

many different OR types

65
Q

T/F: the combination of which OR types are activated determines the odor that is perceived

A

true

66
Q

can a single odorant activate multiple types of ORNs?

A

yes

67
Q

what happens upon odorant binding by ORs?

A

there is a depolarization in the cilia of ORNs, whose unmyelinated axons form fila that pass through the cribriform plate and make their way to the olfactory bulb at the base of the skull

68
Q

where do ORNs terminate in the olfactory bulb?

A

in glomeruli

69
Q

projection neurons (______) send their axons to the ______

A

mitral cells or tufted cells, olfactory cortex

70
Q

upon regeneration, ORNs have to make their way back to the….

A

exact same glomerulus

71
Q

ORNs expressing a specific OR ____ onto a _____

A

converge, single glomerulus

72
Q

glomeruli

A

the synapses between ORNs and mitral cells

73
Q

what are the 6 layers of the olfactory bulb?

A

granule cell layer, internal plexiform layer, mitral cell layer, external plexiform layer, glomerulus layer (GL?)

74
Q

____ are the main projection neurons and form the ____ of the olfactory bulb

A

mitral cells, mitral cell layer

75
Q

____ form the ______

A

tufted cells, external plexiform layer

76
Q

______ form the _____ and send dendrites to mitral cells

A

granule cells, granule layer

77
Q

_____ form the ______ which helps synchronize activity within olfactory bulbs

A

PG cells, periglomerular layer

78
Q

label this diagram:

A

a: GL
b: external plexiform layer
c: MCL
d: IPL
e: GCL
f: PG cell, sSA cell
g: tufted cell
h: mitral cell
i: IPL
j: granule cell

79
Q

mitral cells send info to various parts of the olfactory cortex:

A

Piriform cortex
Olfactory tubercle
Amygdala
Entorhinal cortex

80
Q

of the areas mitral cells send info to, they project olfactory info to the ….

A

thalamus, hypothalamus, hippocampus, and orbitofrontal cortex.

81
Q

animals use the timing of the ____ to determine where odors are in time

A

sniff cycle

82
Q

activity of what cell is timed with the sniff cycle?

A

mitral cell activity

83
Q

______ encode the _____ of an olfactory input into their _____ relative to the sniff cycle

A

mitral cells, strength, firing phases

84
Q

T/F: mtiral cell behaviour does not vary with odors

A

false, it varies depending on the type of odor ( may be sustained or burst firing)

85
Q

____ can depolarize ORN in response to blue light (~470nm)

A

ChR2

86
Q

what can researchers use to drive ChR2 expression in all ORNs?

A

OMP promoter

87
Q

what have studies shown if you stimulate ORNs directly using optogenetics?

A

that mice can learn to perform well on a go/no-go olfactory perception task.

88
Q

using optogenetic approach, you can also…

A

train mice to lick (“go”) only if the odorant is perceived at a certain range of time in the sniff cycle (phase discrimination)

89
Q

what happen even if the go and no go signal are only 10ms apart?

A

the mice still perform above chance; this tells us that the olfactory system is very temporally precise.

90
Q

_______ as a response to an odorant can happen in ______ but also different points in time depending on the ____

A

glomerular activation, different spatial locations, odorant

91
Q

Is the spatial code or the temporal code more important?

A

One study studied the effects of changing spatial and temporal activation of glomeruli through an optogenetic approach, and seeing if it had any effect on mice’s perception of odorant stimuli.

92
Q

Validation/set-up of model: before answering the question, researchers…

A

Determined if optogenetic ChR2 activation resulted in mitral cell firing, and if this firing resulted in odorant perception.

93
Q

taught mice to ____ on a go/no-go task using the _____

A

80% accuracy, optogenetic stimulation

94
Q

after validating their model they changed…

A
  1. the order the glomeruli were activated
  2. which glomeruli were activated
95
Q
  1. the order the glomeruli were activated…
A

the same glomeruli were activated, but in different orders.

96
Q

the further the temporal shift from the original activation pattern….

A

the worse the mice performed.

97
Q

a very detrimental effect was seen when

A

the glomerulus that was normally activated first was shifted enough to make another glomerulus activated before it (sequence-dependent)

98
Q
  1. which glomeruli were activated…
A

replacing a portion of glomeruli with other ones.

99
Q

the greatest detrimental effect was seen…

A

when the glomerulus that would be activated first was replaced.

100
Q

the more glomeruli replace…

A

the worse mouse performed

BIOL 404 FINAL (8 decks)

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