Olfaction

Question 1

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

Answer 1

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

Question 2

What are the 3 chemical senses?

Answer 2

Taste
Smell
Detection of pheromones

Question 3

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

Answer 3

Accessory olfactory pathway (Vomeronasal pathway) and main olfactory pathway

Question 4

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

Answer 4

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

Question 5

Describe the human main olfactory bulb

Answer 5

It is much smaller than other mammal olfactory bulbs

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

Describe the chemical properties of an effective odorant

Answer 8

Should be a small molecule which is volatile

Question 9

Odorants can be grouped these 2 ways

Answer 9

By chemical structure/type and by concentration

Question 10

What are 4 requirements of the olfactory system?

Answer 10

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

Question 11

The sensory neurons from the MOE project to…

Answer 11

The main olfactory bulb (MOB)

Question 12

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

Answer 12

The glomeruli

Question 13

Where are glomeruli located?

Answer 13

In the olfactory bulb

Question 14

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

Answer 14

On the cilia of the olfactory neurons of the MOE

Question 15

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

Answer 15

Glomeruli

Question 16

Define anosmia

Answer 16

Loss of smell

Question 17

More common than complete anosmia is..

Answer 17

Partial anosmia, the loss of certain smells

Question 18

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

Answer 18

Parkinson’s and Alzheimer’s

Question 19

Partial anosmias are common with these kinds of odors

Answer 19

Musk odors

Question 20

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

Answer 20

Apetite

Question 21

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

Answer 21

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

True

Question 23

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

Answer 23

Bipolar

Question 24

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

Answer 24

Buck and Axel

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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?

Answer 27

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!

Question 28

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

Answer 28

In general: one receptor type per neuron!

Question 29

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

Answer 29

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

Question 30

Are olfactory receptors exclusive to the main olfactory epithelium?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

V1Rs and V2Rs

Question 33

What are the 5 classes of olfactory receptors?

Answer 33

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

Question 34

Describe combinatorial coding in olfactory receptors

Answer 34

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

Question 35

What is the advantage of combinatorial coding?

Answer 35

Uses fewer receptors to get more specificity

Question 36

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

Answer 36

Multiple

Question 37

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

Answer 37

Multiple

Question 38

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

Answer 38

Mitral cells

Question 39

What are the key interneurons of the olfactory system?

Answer 39

Periglomerular cells and granule cells

Question 40

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

Answer 40

Horizontal and amacrine cells

Question 41

Describe the organization of the MOE and MOB

Answer 41

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

Question 42

What is the average life span of OSNs?

Answer 42

30-60 days

Question 43

Are OSNs replaced throughout life, or post-mitotic?

Answer 43

Replaced throughout life

Question 44

The stem cells which replace OSNs are called...

Answer 44

Basal cells

Question 45

Axons of like OSNs terminate in...

Answer 45

The same glomerulus

Question 46

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

Answer 46

Granule cell

Question 47

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

Answer 47

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

Question 48

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

Answer 48

True

Question 49

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

Answer 49

1. Subventricular zone of the lateral ventricles 2. Subgranular zone of the dentate gyrus Both in the hippocampus!

Question 50

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

Answer 50

Rostrally to the olfactory bulb

Question 51

Describe birth dating of olfactory neurons

Answer 51

Inject BrdU into cells and detect using BrdU sensitive antibody BrdU labels cells in S-phase Can observe where they migrate into the brain

Question 52

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

Answer 52

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

Question 53

Similar molecules tend to activate glomeruli which are...

Answer 53

Near each other

Question 54

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

Answer 54

Dendrodendritic synapses

Question 55

Dendrodendritic synapses in the olfactory system occur between these cell types

Answer 55

Mitral and granule cells

Question 56

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

Answer 56

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

Question 57

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

Answer 57

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

Question 58

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

Answer 58

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

Question 59

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

Answer 59

Axon pathfinding

Question 60

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

Answer 60

Will become granule and periglomerular cells

Question 61

Do granule and periglomerular cells express olfactory receptors?

Answer 61

No

Question 62

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

Answer 62

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

Question 63

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

Answer 63

The gruenberg ganglion and the septal organ of masera

Question 64

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

Answer 64

Primers and releasers

Question 65

V1Rs use this kind of G protein

Answer 65

Galpha i2

Question 66

V2Rs use this kind of G protein

Answer 66

Galpha o

Question 67

How many V1R receptors have been found in humans?

Answer 67

5

Question 68

How many V2R receptors have been found in humans?

Answer 68

None

Question 69

Where are human V1Rs expressed?

Answer 69

In the MOE

Question 70

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

Answer 70

V1Rs closer to lumen

Question 71

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

Answer 71

2-heptanone

Question 72

Do humans have a VNO?

Answer 72

No

Question 73

V2R are coexpressed with these molecules

Answer 73

MHC class Ib

Question 74

The proposed reason why V2Rs and MHC molecules are coexpressed is... Why do we think this?

Answer 74

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

Question 75

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

Answer 75

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

Question 76

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

Answer 76

Use different G-proteins V1R: Gai2 V2R: Gao

Question 77

Describe the general projections of the cells in the VNO

Answer 77

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

Question 78

Describe the ordering of glomeruli in the AOS

Answer 78

Not quite as ordered as the main olfactory system

Question 79

Describe the projection organ to organ of the vomeronasal system

Answer 79

VNO > AOB > Amygdala > Hypothalamus

Question 80

Describe the projection organ to organ of the main olfactory system

Answer 80

MOE > MOB > Piriform cortex + friends > Thalamus

Question 81

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

Answer 81

The amygdala

Question 82

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

Answer 82

The hypothalamus

Question 83

What of the 5 tastes are aversive?

Answer 83

Sour, salty, and bitter

Question 84

What is the key nutrient being detected by "sour" neurons

Answer 84

Protons (H+)

Question 85

True or false: the tongue has an intrinsic taste map

Answer 85

False

Question 86

Name the different coloured areas of papillae

Answer 86

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