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Neuroscience - Unit 5 > Lecture 9 - Olfaction and Taste > Flashcards

Lecture 9 - Olfaction and Taste Flashcards

1
Q

The receptor cells that transduce odorant stimulu are

A

bona fide neurons.

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2
Q

The cell bodies are located in

A

the olfactory epithelium (OE)

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3
Q

In humans the OE lines what?

A

the posterodorsal part of the nasal cavity below the cribriform plate on the nasal septum and lateral nasal wall.

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4
Q

The OE neurons relay information via

A

axonal projections through the cribriform plate to the olfactory bulb (OB).

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5
Q

The OB is

A

the first relay in the sensory chain.

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6
Q

What drains through the cribiform plate and what is the clinical relevance?

A

CSF drains through and is a potential opening for infection

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7
Q

What is the connection between emotion and smell?

A

The orbitofrontal cortex

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8
Q

What are the OB targets?

A

1) pyriform cortex 2) olfactory tubercle 3) amygdale 4) entorhinal cortex

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9
Q

Senory neuron in the OE

A

1) true sensory neuron 2) death of the sensory neurons leaves the tracks that the new axons can fill

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10
Q

Why might a patient smell an apple that smells like something else?

A

Death of a lot of sensory neurons in the OE result in the incoming axons forming new connections which changes the perception

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11
Q

Bulbar neurons

A

project via the lateral olfactory tract to the piriform (olfactory) cortex located at the tip of the temporal lobe.

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12
Q

What happens to the information after it gets to the olfactory cortex?

A

From here information flows in many directions: to parts of the neocortex via the mediodorsal nucleus of the thalamus and to the lateral hypothalamus

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13
Q

The OE contains:

A

basal cells, neurons and supporting cells.

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14
Q

The neurons of the OE are?

A

bipolar with an apical dendrite ending in a knob with immotile cilia. Each neuron also has a thin unmyelinated axon (C fiber) that projects to the bulb.

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15
Q

Neurogenesis in the olfactory epithelium

A

Basal cells continually undergo mitotic division in a stem cell mode. Sensory neurons have a life span of approx. 30 days. Therefore, epithelial projections are continually being broken down and reforming

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16
Q

What is the sequence of stimulus transduction?

A

(1)odorant delivered to the epithelium along the airstream (2)odorant diffuses through the mucus to reach the cilia (3)odorant interacts with receptor protein (4)binding to the receptor results in a depolarizing receptor potential (5)the biochemistry of t

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17
Q

What is the key ion in the sequence of stimulus transduction?

A

Ca

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18
Q

What is the largest GPCR family?

A

Olfactory receptors

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19
Q

What is the effect of a zonal distribution pattern?

A

Spatial pattern code where there is integration of the receptor type with differing binding affinity

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20
Q

What underlies odor coding?

A

Receptor expression patterns

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21
Q

Describe the olfactory receptor within a zone?

A

Can be either homogenously distributed or have a clustered distribution pattern

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22
Q

Are olfactory receptors specific?

A

Receptors are promiscuous with what they respond to

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23
Q

Single unit recordings of individual olfactory sensory neurons show what?

A

That neurons are broadly tuned.

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24
Q

The diversity of physiologically defined types of olfactory neurons parallels what?

A

the number of ORs.

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25
Q

What determines the physiological responsiveness of an olfactory neuron?

A

the particular OR a neuron expresses where any one OR is broadly tuned to respond to a lot of different odorants, which share a common molecular feature.

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26
Q

The encoding of odorants at the level of the olfactory epithelium is

A

spatial

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27
Q

Compare the areas of the epithelium in their response to odorants.

A

There are inherent or intrinsic differences

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28
Q

The inherent differences in response to odorants reflect what?

A

the distribution of ORs

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29
Q

What is the result of inherent differences in response to odorants?

A

Each odorant has its own fingerprint

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30
Q

What is the most rostral part of the CNS?

A

The olfactory bulb

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31
Q

What is the shape of the olfactory bulb and its cells?

A

It is tubular in shape and the cells and their neuropil are arranged in concentric layers like an onion.

32
Q

What is the order for the layers of the olfactory bulb?

A

there is the glomerular layer, external plexiform layer, mitral cell layer and granule cell layer.

33
Q

What are the mitral and tufted cells?

A

they are the relay neurons that project to olfactory cortex.

34
Q

What are Periglomerular cells and granule cell?

A

they are inhibitory interneurons that modulate activity of the mitral tufted cells.

35
Q

What do the periglomerular cells form?

A

the outmost shell of neurons. They cluster around neuropils called glomeruli.

36
Q

What is the fundamental unit of anatomical and physiological organization in the bulb?

A

The glomerulus

37
Q

How does the olfactory sensory system compare other sensory systems?

A

1) the projection of the sensory surface onto its central structures is not point-to-point. (2) First, it is quadrant-to-quadrant. These quadrants are defined by the boundaries of the OR expression zones.

38
Q

What defines the quadrants of the olfactory sensory systems?

A

The boundaries of the OR expression zones

39
Q

What is meant by a differential distribution pattern of specific OR expressing neurons?

A

1) any particular neuron expresses but one OR type 2) within a zone, neurons expressing a particular OR can be either homogenously distributed or have a clustered distribution pattern

40
Q

What is the convergence of axons axons from specific OR expressing neurons?

A

Second, within a quadrant the axonal projections bring together the axon terminals of all “like-neurons”. In other words, all of the neurons expressing a particular OR converge onto the same set of glomeruli.

41
Q

all of the neurons expressing a particular OR

A

converge onto the same set of glomeruli

42
Q

What is responsible for establishing the spatial code for olfactory stimuli across the bulb?

A

The pattern of the projections from the epithelium onto the bulb. The circuitry then acts on this information.

43
Q

Describe the olfactory neurons and the olfactory receptor.

A

Recall that olfactory neurons are broadly tuned and that all the neurons that express a single OR synapse together in a single glomerulus. Thus, the rule – one OR, one glomerulus applies

44
Q

The glomerulus is

A

both an anatomical unit and a functional unit.

45
Q

The glomerulus as both an anatomical and functional unit is implied by what?

A

the connectivity, the unique responsiveness of individual ORs and, like the epithelium, the pattern of activation of the bulb in response to odorants.

46
Q

Lateral inhibition

A

filters out the incidental information from the true stimulus

47
Q

Glomeruli are activated by what?

A

odorants and different glomeruli are activated by different odorants.

48
Q

In the working model for the olfactory system, what is an odotype?

A

there are many different ORs and each would recognize a single chemical moiety (e.g., a phenyl group) that would be considered an “odotope”. A single chemical would be composed of many such odotopes.

49
Q

In the working model for the olfactory system, how are odors identified and discriminated?

A

by the overall activation of glomeruli across a the whole bulb based on the selective activation of glomeruli, one glomerulus is the unit for recognizing a particular odotope that has been presented

50
Q

The five primary taste qualities are:

A

salt, sour, bitter, sweet and umami

51
Q

Taste buds are innervated by

A

cranial nerves (VII via the chorda tympani nerve to the tongue and the greater superficial petrosal to the palate), and the IXth and Xth). Each axon innvervates from 2-10 taste cells

52
Q

Gustatory axons innervate what?

A

the NTS (nucleous of the solitary tract).

53
Q

The NTS has projections to

A

1) VPM of the thalamus 2) hypothalamus 3) amygda.

54
Q

VPM, the hypothalamus and the amygdala project to what?

A

the insula and frontal cortex.

55
Q

Taste buds on the anterior 2/3s of the tongue

A

CN VII

56
Q

Taste buds on the posterior 1/3 of the tongue

A

CN IX

57
Q

Taste buds for the epiglottis

A

CN X

58
Q

What are the four primary taste fields?

A

1) circumvallate 2) foliate 3) fungiform papillae 4) buds on the soft palate.

59
Q

What taste fields respond to what tastants?

A

All of the taste fields respond to all tastants, each taste field is most sensitive to a particular taste quality.

60
Q

What taste buds are most sensitive to sweet?

A

the soft palate

61
Q

Taste buds are limited to

A

specialized protrusions called papillae

62
Q

Describe a taste bud.

A

pear-shaped collection of cells surrounded by a basal lamina that are embedded in a stratified squamous epithelium.Each bud has 50-100 cells that include receptor cells and basal cells (stem cells).

63
Q

Microvilli of a taste cell extends through what?

A

a taste pore.

64
Q

What synapses with the receptor (taste) cells?

A

Gustatory afferent axons

65
Q

Stimuli (of the taste cell) causes what?

A

a deplorization which produce synaptic transmission across the receptor cell – axon synapse.

66
Q

Salt and sour stimuli are transduced through

A

an ionic transduction mechanism which results in an intracellular increase in calcium and transmitter release.

67
Q

Salt ion transduction mechanism

A

amiloride sensitive Na channel

68
Q

Acid ion transduction mechanism

A

H+ sensitive cation channel

69
Q

Receptor mediated transduction via second messenger in taste

A

Sweet, bitter and umami stimuli are transduced through a G-protein coupled mechanism. Increases in cAMP stimulate a TRPM5 calcium channel via IP3. Take home point = increase Ca influx

70
Q

In the gustatory system, what do single axons respond to?

A

many different primary stimulus qualities although they will have a preferential maximal response to only one.

71
Q

Recoding activity patterns for the gustatory system from the chorda tympani nerve?

A

one can demonstrate a differential firing pattern across a population of axons.

72
Q

What was seen as the evidence for an across fiber “pattern code”?

A

a differential firing pattern across a population of axons

73
Q

How does the same group of axons in the gustatory system differentially encode the stimulus quality?

A

It does this based on the differential firing pattern.

74
Q

What does the evidence for labeled line taste coding suggest?

A

that specific gene knockout and rescue experiments specifically rescue or delete the perception of one taste quality without impacting the others.

75
Q

Deletion in mice of a downstream transduction component (i.e., PLC beta 2) of all three tastants results in what?

A

an altered behavioral response to the stimulus qualities.

76
Q

When PLC beta 2 is specifically rescued in cells that express the taste receptors for bitter (T2Rs) what is seen?

A

there is a recovery of function for quinine but not the other tastants.

77
Q

Pungency vs odor

A

1) Pungency = irritation ex capsacin transmitted through lingual nerve through Trigeminal 2) Odor is through the ORs of CN I

Neuroscience - Unit 5 (12 decks)

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