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Neuroscience > Olfaction and gustation > Flashcards

Olfaction and gustation Flashcards

1
Q

How do humans detect and respond to environmental and internal chemicals?

A

Chemoreception (olfaction, taste, chemosensory irritants and carotid bodies)

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2
Q

Where is the site of olfaction?

A

The nasal cavity

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3
Q

Where is the olfactory mucosa?

A

Present in the upper posterior regions where the axons push through holes in the cribriform plate

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4
Q

Are olfactory axons myelinated or unmyelinated?

A

Unmyelinated

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5
Q

Where do olfactory axons project to?

A

Olfactory bulb

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6
Q

How do the olfactory axons terminate?

A

Apical thin dendrites which form specialised cilia that carry odorant receptors

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7
Q

What three cell types make up the olfactory mucosa?

A

Olfactory receptor/sensory neurons (OR/SN)

Basal cells: stem cells

Supporting cells

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8
Q

How often are olfactory sensory neurons replaced?

A

Continually regenerated, from basal cells, every 4-8 weeks, very unusual as part of the CNS.

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9
Q

Why are olfactory sensory neurons unusual?

A

Some of the only neurons which are continually regenerated

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10
Q

What receptor is the olfactory receptor?

A

GPCR

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11
Q

What does the OR bind?

A

Small molecules (over 400,000 substances)

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12
Q

What is the receptive range/detection threshold of ORs?

A

Can vary (broad or narrow) (0.01nM - 2mM)

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13
Q

To be detected, what must the odorant be?

A

Dissolved in mucous

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14
Q

What happens when odorant binds OR?

A

Binding of odorant activates (Gs) → activation of adenylate cyclase III (specific) → upregulation of cAMP → opening of cyclic nucleotide gated channels (CNG) → Ca2+ influx and depolarisaon → opening of calcium-activated Cl- channels (ANO2) → chloride exits the cell leading to further depolarisation→ ACTION POTENTIAL → NT release.

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15
Q

How is odorant signal switched off?

A

NCKX4 - pump out calcium

Calcium adaptation reduces scent sensitivity, calcium dependent activation of PDE (lower cAMP) (fast adaptation)

CalCaM formation acts to inhibit Ca2+ input (slow adaptation)

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16
Q

What are the layers of the olfactory bulb (out to in)?

A

Olfactory neuron layer (ONL)

Glomerular layer (GL)

External plexiform layer (EPL)

Mitral cell layer (MCL)

Granule cell layer (GCL)

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17
Q

How is the olfactory neuron layer positioned in the olfactory bulb compared to the glomerular layer?

A

Interspersed

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18
Q

What effect does an increase in odorant concentration have on the upstream effects?

A

Increase in activity per glomerulus and increase in the number of active glomeruli

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19
Q

What are the projection neurons of the olfactory bulb?

A

Mitral cells

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20
Q

What do the ORNs contact?

A

Mitral cells

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21
Q

Where do mitral cells project?

A

Mitral cells project to the olfactory cortex

Secondary olfactory cortex

Contralateral olfactory bulb

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22
Q

Does olfaction pass through the thalamus before cortex?

A

NO

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23
Q

What is the only sensory modality not to pass through the thalamus?

A

Olfaction

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24
Q

What is the role of the periglomerular and granule cells?

A

Provide lateral inhibition

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25
Q

Where is the olfactory cortex?

A

Temporal lobe (in front of A1 just beneath the lateral sulcus)

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26
Q

What part of the parahippocampal gyrus does the olfactory cortex lie on?

A

Uncus

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27
Q

What is the role of O1?

A

Emotional, motivational, autonomic and endocrine response

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28
Q

What is the role of O2?

A

Conscious discrimination of different smells

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29
Q

Where do all central projections feedback?

A

Olfactory bulb

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30
Q

What is the olfactory tubercle?

A

A region of the olfactory cortex

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31
Q

Where does the medial olfactory striae connect?

A

Orbitofrontal cortex

32
Q

Where does the lateral olfactory striae connect

A

Parahippocampal gyrus (memory of smells), amygdala (emotion of smell)

33
Q

Where does the lateral olfactory striae connect

A

Piriform cortex (O1), Parahippocampal gyrus (memory of smells), amygdala (emotion of smell)

34
Q

What does the olfactory tract branch into?

A

Lateral olfactory striae (brings to uncus), medial olfactory striae (subcallosal gyrus and OFC)

35
Q

What are pheromones?

A

Substance that is utilised for intra-species communications

Released by one individual and received by conspecifics

Send information about sex, strain and species to receiver

Are meaningful or informative for species

36
Q

What is anosmia?

A

Inability to detect presence of odour

37
Q

What is Phantosmia?

A

Perception of odour in absence of odour source

38
Q

What is Parosmia?

A

Sensation of odour distinct from that present

39
Q

What is Dysosmia?

A

Difficulty with odour discrimination

40
Q

What are common features of tastants?

A 
Non-volatile	
Hydrophilic 
Soluble in saliva 
Detection threshold high 
Low mM range (except bitter substances: nM range – Strychnine: 0.1 nM)
41
Q

What is a papillae?

A

Small bumps on the tongue

42
Q

What is the benefit of papillae?

A

Creates local invagination in tongue epithelium (“trench”) to concentrate solubilised tastant

43
Q

What makes up a papillae?

A

Taste buds

44
Q

What are taste buds made up of?

A

Taste cells

45
Q

How many taste buds?

A

5000

46
Q

How many taste cells per bud?

A

5-150

47
Q

What is a circumvallate papilla?

A

At junction oral & pharyngeal part, hundreds of taste cells

48
Q

What is a foliate papilla?

A

Sides at rear, many taste cells

49
Q

What is a fungiform papilla?

A

Around front & edge of tongue, few taste cells

50
Q

What is a filiform papilla?

A

All over, tactile

51
Q

Taste receptors for which 5 different taste modalities?

A

Salt: electrolytes ingested
Bitter/sour: protection of toxic chemicals
Sweet: high energy content
Umami: high amino acid content

52
Q

What cells make up taste buds?

A

Taste receptor cells, support cells, basal cells

53
Q

What is the lifetime of taste receptor cells?

A

~2 weeks

54
Q

What is at the apical surface of a taste receptor cell?

A

Microvilli

55
Q

What are the three models for encoding taste?

A

Taste receptor cells express a number of different taste receptors. Taste recognition results from decoding the combined activity of various classes of taste receptor cells.

Taste receptor cells express one family of taste receptors but several taste receptor cells contact the same afferent neuron Taste recognition results from
decoding the combined activity of various afferents

Labelled line model: Taste receptor cells express one family of taste receptors and are connected to afferents that are specific for the taste receptor expressed

56
Q

What is the most likely model?

A

Taste receptor cells express a number of different taste receptors. Taste recognition results from decoding the combined activity of various classes of taste receptor cells.

57
Q

What is the most likely model?

A

Labelled line model: Taste receptor cells express one family of taste receptors and are connected to afferents that are specific for the taste receptor expressed

58
Q

Describe sour taste receptors

A 
Local stimulus: H+ 
Unclear receptor(s):

(PKD2L1, PKD1L3 (Polycystic Kidney Disease-Like protein = Transient Receptor Potential Polycystic (TRPP) channel)

59
Q

What receptors are sweet, bitter and umami

A

GPCRs

(Gq), Beta-gamma subunit then activates PLC, IP3 liberated Ca2+ from intracellular Ca2+ stores, Calcium then leads to activation of calcium dependent TRPM5 channel.

Na+ entry and depolarisation

60
Q

How does temperature influence taste?

A

Sweet taste is enhanced by warm temperature: GPCR leads to Ca2+-dependent opening of TRPM5 channels.

TRPM5 channels are temperature-sensitive between 15 - 35ᵒC

61
Q

What nerves carry taste information?

A

Facial (VII) (anterior 2/3) and glossopharyngeal (IX) (posterior 1/3).

62
Q

Where do taste nerves project?

A

Facial & glossopharyngeal nerves project taste fibres to the nucleus of the solitary tract in the medulla

63
Q

Where do second order taste neurons project?

A

Second order neurons pass to ventral-posterior nucleus of the thalamus

64
Q

Where does gustatory information from the thalamus pass to?

A

Primary taste cortex (insula/opercula) and secondary taste cortex (orbitofrontal)

65
Q

What is hypogeusia?

A

Decreased sensitivity to taste

66
Q

What is dysgeusia?

A

Taste confusion

67
Q

What is phantogeusia?

A

Phantom taste

68
Q

What is ageusia?

A

Loss of taste

69
Q

Where are the two sites of adult neurogenesis?

A

Olfactory bulb and hippocampus (dentate gyrus)

70
Q

The olfactory and taste system have in common that..

A

They both project to the hypothalamus and orbitofrontal cortex

71
Q

Olfactory receptor cells convey information directly to the…

A

Mitral cells which form the neurons of the olfactory bulb

72
Q

Olfactory axons pass through the

A

Cribriform plate

73
Q

The primary olfactory cortex is located in the

A

Piriform cortex (part of the rhinencephalon)

74
Q

Cortex receiving directly from the olfactory bulb is situated in the

A

Telencephalon

75
Q

Olfactory nerves enter the cranium via the cribriform plate of which bone?

A

Ethmoid

76
Q

The medial part of the olfactory tracts projects to the opposite olfactory bulb via the

A

Anterior commissure

77
Q

The lateral division of the olfactory tract sends fibres to the

A

Amygdala

Neuroscience (19 decks)

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