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Y2S2M1 > The Somatosensory System: Taste and Smell > Flashcards

The Somatosensory System: Taste and Smell Flashcards

1
Q

What is taste and smell in their basic form?

A

In their basic form, taste and smell is just the chemoreception of particular types of chemicals

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2
Q

What is required for us to be able to sense chemicals?

A

Sensing chemicals requires chemoreceptors.

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3
Q

What is the advantage of the ability to sense chemicals?

A

Sensing chemicals allows organisms to perform diverse functions: finding out things about their location, finding food, finding a mate, avoiding danger/dangerous substances, and maintaining homeostasis.

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4
Q

What is the advantage of having taste and smell?

A

Taste and smell are important for environmental chemical detection, helping us avoid toxins and poisons, and enhancing nutrition by making eating a more pleasurable experience.

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5
Q

Which of the two (smell vs taste) is a bigger contributor to flavour?

A

Smell is a bigger contributor.

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6
Q

What are the clinical implications of taste and smell?

A

It is possible to have an under or over perception of taste and smell, or to completely lose it altogether. Ageusia = total loss of taste, Anosmia = total loss of smell.

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7
Q

What are the consequences of alteration/loss of taste/smell?

A

An alteration/loss of taste/smell may have nutritional/toxicity consequences on an individual.

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8
Q

What can impact our sense of taste and smell?

A

Age, drugs, and lesions (clinical conditions).

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9
Q

What happens to smell and taste as we age?

A

Normal aging often results in diminishing of taste and smell, which can lead to poor nutrition.

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10
Q

How can drugs impact our ability to taste and smell?

A

Changes may be due to changes in ions, saliva production, and neurotransmission.

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11
Q

What types of drugs can alter our ability to taste and smell?

A

Drugs used for mental health conditions and chemotherapy drugs can affect taste and smell.

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12
Q

What needs to happen before chemicals in food can access chemoreceptors?

A

Chemicals in our food need to be dissolved in saliva.

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13
Q

What are drugs which affect taste and smell associated with?

A

Any drug that might affect taste and smell may be associated with compliance issues.

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14
Q

What clinical conditions affect smell?

A

Notable conditions include damage along the neurone pathway, changes in brain activity, damage to olfactory bulbs, neurodegenerative diseases, and major depressive disorder.

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15
Q

What are the 5 basic tastes?

A

Salt, sour, sweet, bitter, umami.

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16
Q

What is umami?

A

Umami is the taste associated with meat and fermented food, relating to monosodium glutamate.

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17
Q

Where are the taste cells that have the chemoreceptors found?

A

Tongue, palate, pharynx.

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18
Q

Are the maps suggesting different regions of the tongue responsible for different tastes accurate?

A

This is a gross oversimplification; taste receptors are distributed throughout the tongue.

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19
Q

What allows the tongue to have a large surface area?

A

The surface of the tongue has a large surface area due to its folded arrangement.

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20
Q

What are the ridges on the tongue known as?

A

On the tongue, different types of ridges are known as papilla.

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21
Q

Where are taste buds found?

A

Taste buds are found on the surface of papilla.

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22
Q

What are the 3 aspects of taste buds?

A

Taste cells, basal cells, and sensory afferents.

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23
Q

Why are taste buds not sensory neurones?

A

Taste cells are not sensory neurones; they cannot produce action potentials.

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24
Q

How do taste cells communicate with the CNS?

A

They are closely associated with sensory afferents and send chemical messages in a synapse-like way.

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25
What is the advantage of taste buds being separate cells from sensory neurones?
Taste cells are constantly dividing and being replaced, on average every 2 weeks.
26
How are new taste cells born?
New taste cells are born from basal cells and this process slows down with age.
27
How do taste cells detect taste?
Taste cells express taste receptor molecules that act as chemoreceptors.
28
What is signal transduction?
The process of converting a stimulus into electrical signals.
29
How do different cells detect different taste sub-modalities?
Different transduction mechanisms (different types of taste receptors) allow for the detection of various sub-modalities.
30
Describe the general signal transduction pathway for taste.
Chemicals bind to receptors on taste cells, causing a receptor potential, opening voltage-gated Ca2+ channels, leading to neurotransmitter release and action potentials.
31
What molecule causes the taste of saltiness?
Saltiness reflects the level of NaCl in food.
32
Describe signal transduction in taste cells that detect saltiness.
NaCl dissolves into ions, and taste cells express an Amiloride sensitive sodium channel allowing Na+ entry, causing depolarization.
33
What molecule causes the taste of sourness?
Sourness comes from acidity, specifically high concentrations of H+.
34
Describe signal transduction in taste cells that detect sourness.
H+ ions can inhibit K+ channels and enter through TRP channels, leading to depolarization and neurotransmitter release.
35
What are TRP channels?
TRP channels are involved in creating a concentration gradient, leading to membrane depolarization.
36
What results from membrane depolarization?
Membrane depolarization results in the opening of VG Ca2+ channels.
37
What receptors are involved in detecting sweet, umami, and bitter tastes?
G-protein coupled taste receptors (GPCRs) are involved in detecting sweet, umami, and bitter tastes.
38
How do sweet, umami, and bitter tastes activate GPCRs?
Sweet, umami, and bitter tastes activate GPCRs by binding to them, leading to membrane depolarization and opening of VG Ca2+ channels.
39
How can we distinguish between sweet, umami, and bitter tastes?
Distinction is based on the different subunits of GPCRs: sweet (T1R2 and T1R3), umami (T1R1 and T1R3), and bitter (T2R family).
40
What is the receptor distribution of taste buds on the tongue?
Taste cells for sweet/umami (T1R3) and bitter (T2R) are intermingled across the tongue, with no overlap in receptor expression.
41
What is the general pathway of taste stimulus to the brain?
Taste information travels through a 3-neurone chain (+ 2 synapses) to the primary cortex, remaining ipsilateral.
42
Which cranial nerves are involved in taste?
Cranial nerves 7 (facial), 9 (glossopharyngeal), and 10 (vagus) are involved in taste.
43
Which parts of the tongue do the cranial nerves innervate?
CNIX innervates the back part (1/3), CNVII innervates the front part (2/3), and CNX innervates non-tongue taste receptors.
44
Describe the pathway of the primary neurone in taste.
The primary neurone carries information from the tongue into the brain via cranial nerves, entering through the brain stem and into the medulla.
45
Where do the primary and secondary neurones synapse in taste?
The primary neurone synapses with the secondary neurone at the gustatory nucleus in the medulla.
46
Where do the secondary neurones carry information in taste?
Secondary neurones carry information from the gustatory nucleus to the thalamus.
47
Where do the tertiary neurones carry information in taste?
Tertiary neurones convey information from the thalamus to the primary gustatory cortex.
48
Where is the primary gustatory cortex located?
Part of the primary gustatory cortex is on the outside of the brain, while part loops around in the fissure between the parietal and temporal lobe.
49
What happens once the third order neurones arrive at the primary cortex?
The primary cortical neurones compare inputs to determine the taste detected, as food contains various sub-modalities.
50
What is the function of side branches in the taste pathway?
Side branches known as collaterals connect to the medulla for swallowing and salivation, and to the hypothalamus for satiety and palatability.
51
Which has greater sensitivity, smell or taste?
Smell has greater sensitivity than taste, as evidenced when a blocked nose reduces flavor perception.
52
Can smell act alone or must it work with taste?
It is unclear if smell can act alone in humans; dogs use smell for location detection.
53
How are smell cells different from taste cells?
Smell cells are neurones that can fire action potentials and are replaced every 4-8 weeks, unlike taste cells which are replaced every 2 weeks.
54
Where are smell receptors found?
Smell receptors are found in the olfactory epithelium in the roof of the nasal cavity.
55
Describe the structure of olfactory receptors.
Olfactory receptors have cilia continuous with their cell bodies, forming long processes that are sensory neurones of the olfactory nerve.
56
How do olfactory receptors detect smell?
Chemicals dissolve in mucus and bind to cilia, generating an action potential that travels along the olfactory nerve.
57
Why can head injuries result in loss of olfaction?
Front-on head injuries can disrupt olfaction due to the weak cribriform plate, which is prone to fracture.
58
How are new smell cells born?
New smell cells are produced from stem cells in the lining of the lateral ventricles, migrating to the olfactory bulb.
59
What ability do lateral ventricles retain?
They retain the ability to have stem cells that can divide to form new neurones.
60
Where are olfactory neurones born?
Olfactory neurones are born in the lining of the lateral ventricles.
61
What is the path of olfactory neurones?
They follow a path to the olfactory bulb where they form new synapses and integrate into new circuits.
62
What could understanding the birth of baby neurones lead to?
It could lead to therapeutic purposes for neurodegenerative diseases.
63
How is Covid-19 associated with a loss of smell?
The virus binds to olfactory neurones and destroys them.
64
How often are olfactory neurones replaced?
Olfactory neurones are replaced every 4-8 weeks.
65
Why might some individuals experience long-term loss of smell after Covid-19?
It may be due to a significant depletion of stem cell reserve.
66
What do olfactory cells contain?
Each olfactory cell contains only one type of chemoreceptor molecule.
67
Is it possible to detect sub-modalities of smell?
It has been impossible to detect sub-modalities of smell.
68
How do chemoreceptor molecules function in the olfactory system?
They can bind to a whole range of odorants, suggesting many types of chemoreceptors.
69
How do we detect smells with multiple chemoreceptors?
Coordinated firing of multiple neurons allows for odorant detection.
70
What is population coding in olfaction?
It is the brain's process of comparing inputs from different olfactory cells to identify smells.
71
What happens in the brain during smell detection?
The brain performs a population decoding exercise to compare inputs from olfactory neurones.
72
What is sensory adaptation?
It is when sensory cells do not transmit information about a stimulus that is present.
73
How does sensory adaptation manifest in olfaction?
You may stop noticing a smell after being in an environment for a while.
74
What is the transduction pathway for olfactory cells?
Odorant binds to a receptor, activating GPCR, leading to depolarization and potential action potential.
75
How do olfactory neurones synapse in the brain?
Neurones that detect the same stimuli synapse together in a glomerulus.
76
Where do first order neurones synapse?
They synapse in the glomerulus within the olfactory bulb.
77
What happens after the second order neurone in the olfactory pathway?
It sends an axon to the olfactory cortex or to limbic areas for smell association.
78
How many neurones are in the olfactory pathway?
There are only 2 neurones in the olfactory pathway from detection to the primary cortex.
79
What is the role of the orbitofrontal cortex in olfaction?
It is involved in the recognition of smell through population coding.
80
What do people with anosmia report about their smell after recovery?
They often report that their smell is altered upon return.
81
Why might smell be altered after recovery from anosmia?
New olfactory cells may mis-wire and not form the correct glomeruli.

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