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Olfaction and gustation Flashcards

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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
Where is the olfactory cortex?
Temporal lobe (in front of A1 just beneath the lateral sulcus)
26
What part of the parahippocampal gyrus does the olfactory cortex lie on?
Uncus
27
What is the role of O1?
Emotional, motivational, autonomic and endocrine response
28
What is the role of O2?
Conscious discrimination of different smells
29
Where do all central projections feedback?
Olfactory bulb
30
What is the olfactory tubercle?
A region of the olfactory cortex
31
Where does the medial olfactory striae connect?
Orbitofrontal cortex
32
Where does the lateral olfactory striae connect
Parahippocampal gyrus (memory of smells), amygdala (emotion of smell)
33
Where does the lateral olfactory striae connect
Piriform cortex (O1), Parahippocampal gyrus (memory of smells), amygdala (emotion of smell)
34
What does the olfactory tract branch into?
Lateral olfactory striae (brings to uncus), medial olfactory striae (subcallosal gyrus and OFC)
35
What are pheromones?
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
What is anosmia?
Inability to detect presence of odour
37
What is Phantosmia?
Perception of odour in absence of odour source
38
What is Parosmia?
Sensation of odour distinct from that present
39
What is Dysosmia?
Difficulty with odour discrimination
40
What are common features of tastants?
``` Non-volatile Hydrophilic Soluble in saliva Detection threshold high Low mM range (except bitter substances: nM range – Strychnine: 0.1 nM) ```
41
What is a papillae?
Small bumps on the tongue
42
What is the benefit of papillae?
Creates local invagination in tongue epithelium (“trench”) to concentrate solubilised tastant
43
What makes up a papillae?
Taste buds
44
What are taste buds made up of?
Taste cells
45
How many taste buds?
5000
46
How many taste cells per bud?
5-150
47
What is a circumvallate papilla?
At junction oral & pharyngeal part, hundreds of taste cells
48
What is a foliate papilla?
Sides at rear, many taste cells
49
What is a fungiform papilla?
Around front & edge of tongue, few taste cells
50
What is a filiform papilla?
All over, tactile
51
Taste receptors for which 5 different taste modalities?
Salt: electrolytes ingested Bitter/sour: protection of toxic chemicals Sweet: high energy content Umami: high amino acid content
52
What cells make up taste buds?
Taste receptor cells, support cells, basal cells
53
What is the lifetime of taste receptor cells?
~2 weeks
54
What is at the apical surface of a taste receptor cell?
Microvilli
55
What are the three models for encoding taste?
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
What is the most likely model?
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
What is the most likely model?
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
Describe sour taste receptors
``` Local stimulus: H+ Unclear receptor(s): ``` (PKD2L1, PKD1L3 (Polycystic Kidney Disease-Like protein = Transient Receptor Potential Polycystic (TRPP) channel)
59
What receptors are sweet, bitter and umami
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
How does temperature influence taste?
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
What nerves carry taste information?
Facial (VII) (anterior 2/3) and glossopharyngeal (IX) (posterior 1/3).
62
Where do taste nerves project?
Facial & glossopharyngeal nerves project taste fibres to the nucleus of the solitary tract in the medulla
63
Where do second order taste neurons project?
Second order neurons pass to ventral-posterior nucleus of the thalamus
64
Where does gustatory information from the thalamus pass to?
Primary taste cortex (insula/opercula) and secondary taste cortex (orbitofrontal)
65
What is hypogeusia?
Decreased sensitivity to taste
66
What is dysgeusia?
Taste confusion
67
What is phantogeusia?
Phantom taste
68
What is ageusia?
Loss of taste
69
Where are the two sites of adult neurogenesis?
Olfactory bulb and hippocampus (dentate gyrus)
70
The olfactory and taste system have in common that..
They both project to the hypothalamus and orbitofrontal cortex
71
Olfactory receptor cells convey information directly to the...
Mitral cells which form the neurons of the olfactory bulb
72
Olfactory axons pass through the
Cribriform plate
73
The primary olfactory cortex is located in the
Piriform cortex (part of the rhinencephalon)
74
Cortex receiving directly from the olfactory bulb is situated in the
Telencephalon
75
Olfactory nerves enter the cranium via the cribriform plate of which bone?
Ethmoid
76
The medial part of the olfactory tracts projects to the opposite olfactory bulb via the
Anterior commissure
77
The lateral division of the olfactory tract sends fibres to the
Amygdala

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