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MBBS2/Physiology~HEAD & NECK > Chemical Senses > Flashcards

Chemical Senses Flashcards

1
Q

What is gustation

A

Taste

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2
Q

What is olfaction

A

Smell

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3
Q

What do chemoreceptors respond to

A

Chemicals in aqueous solution

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4
Q

Taste receptors respond to what

A

Substances dissolved in saliva

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5
Q

What do smell receptors respond to

A

Substances dissolved in fluids of nasal membranes

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6
Q

What does the taste system evaluate

A

Potential food for nutritional and poisonous chemical features

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7
Q

What does flavor of food depend on

A

A combination of taste, smell, texture and temperature

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8
Q

Sense of gustation depends on what

A

Chemical stimuli and tastants present in food

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9
Q

Where do you find taste buds

A

On the dorsal surface of the tongue in papillae

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10
Q

What papillae do you find on the anterior dorsal surface of the tongue

A

Fungiform

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11
Q

What papillae do you find on the posterior and lateral dorsal surface of the tongue

A

Foliate

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12
Q

What papillae do you find on the base of the dorsal surface of the tongue

A

Circumvallate

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13
Q

Where can taste buds also occur

A

-soft palate
-pharynx
-epiglottis

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14
Q

What cells make up taste buds

A

-chemoreceptors ( about 50-150 taste receptor cells)
-supporting cells (sustentacular cell)
-basal cells

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15
Q

How many taste buds do adults have

A

3000- 10 000

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16
Q

How many taste buds does each papillae have

A

1- several hundred

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17
Q

What happens to taste buds with age

A

They degenerate

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18
Q

The apex of taste chemoreceptors have what

A

Microvilli

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19
Q

Chemoreceptors (taste cells) synapse with what

A

Afferent neurons

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20
Q

Taste chemoreceptors are continually replaced by what

A

Mitotic division of the surrounding epithelial cells

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21
Q

What do taste chemoreceptors detect

A

Stimulatory molecules that diffuse into the taste pore from the overlaying fluid layer

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22
Q

What are the basic tastes

A

-sour
-salty
-sweet
-bitter
-umami

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23
Q

What causes the sour taste

A

Acids I.e. the H+ conc

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24
Q

What causes salty taste

A

Ionized salts ,mainly the Na+ conc

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25
Q

The sweet taste isn’t caused by what

A

A single class of chemicals

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26
Q

What causes the sweet taste

A

Sugars, glycols, aldehydes, ketones, amides, esters, some amino acids, some small proteins, sulfonic acids, halogenated acids and inorganic salts of lead and beryllium

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27
Q

The bitter taste isn’t caused by what

A

Any single type of chemical agent

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28
Q

What causes the bitter taste

A

Long chain organic substances that contain nitrogen and alkaloids e.g. quinine, caffeine, nicotine and strychnine

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29
Q

Some substances that are first sweet have what

A

Have a bitter aftertaste d.g. Saccharine

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30
Q

What is the umami taste

A

-It’s delicious…it has a pleasant taste sensation that is qualitatively different from the other tastes

-it’s the dominant taste of food containing L-glutamate e.g. meaty extracts

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31
Q

What’s the chemoelectrical transduction for salty taste

A

-Na+ flow into taste cells through the apical amiloride sensitive Na+ channels
-this depolarizes the taste cell
-voltage-dependant Ca2+ channels open
- there is an influx in Ca2+
-Ca2+ causes serotonin vesicles to release their neurotransmitter which then stimulates the afferent taste axon

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32
Q

What’s the chemoelectrical transduction for sour taste

A

-H+ enter the cell through proton selective ion channels
-the H+ depolarize the taste cell
-this opens voltage-dependent Ca2+ channels
-this causes an influx of Ca2+
- Ca2+ causes the release of the neurotransmitter serotonin, which stimulates the afferent taste axons
-the H+ also blocks K+ channels, which causes an increase of K+ and that adds to the chemoreceptor depolarization

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33
Q

What else can elicit sour sensation

A

Potassium channel blockers eg tetraethylammonium

34
Q

What’s the chemical transduction for bitter, sweet and umami taste

A
  • compounds from these tastes activate taste receptor cells via the G protein coupled receptors
  • when they bind to the G protein receptor this activates phospholipase C into IP3
    -IP3 causes the release of Ca2+ from the ER
    -Ca2+ release then causes the neurotransmitter ATP to be released
35
Q

Why is Ca2+ influx not needed in the chemoelectrical transduction of bitter/sweet/umami

A

Because ATP isn’t released from vesicles

36
Q

Taste buds are innervated by what

A

-facial nerve (chorda tympani) (anterior 2/3 of tongue)
-glossopharyngeal nerve (posterior 1/3 of tongue)
-vagus nerve (palate, pharynx and epiglottis)

37
Q

What is the central pathway for taste

A
  • the taste fibers ( 1st order neurons/ afferent gustatory neurons ) synapse in the gustatory division of the solitary nucleus in the medulla
    -the 2nd order neurons then synapse in the ventral posterior medial nucleus of the thalamus
    -the 3rd order neuron carries signals to the primary gustatory cortex

-from the gustatory nucleus in the brain stem taste pathways diverge to:
1. Cerebral cortex i.e. somatosensory and frontal cortex for conscious perception of taste
2. Brain stem regions involving swallowing, salivation, gagging, vomiting, digestion and respiration
3. Limbic system i.e. amygdala and hypothalamus for food palatability and motivation to eat
4. Hippocampus for food memory

38
Q

Taste disorders are the result of what

A

Medical conditions
Pharmacological or surgical interventions
Environmental exposure to toxic chemicals
Head injury
Poor oral hygiene
Advanced age

39
Q

Whats hypogeusia

A

A diminished sense of taste

40
Q

Whats ageusia

A

A complete loss of taste

41
Q

What’s dysgeusia

A

An alteration/ distortion in the perception of taste

42
Q

What’s phantogeusia

A

It’s a phantom taste which is often a bitter or metallic taste when no gustatory stimuli is present

43
Q

People with what conditions experience phantogeusia

A

-schizophrenia
-seizure aura for focal epilepsy

44
Q

olfaction serves as an early what

A

Warning system for detection of fire
Dangerous fumes
Polluted environments

45
Q

Olfaction largely determines what

A

The flavor and palatability of food and beverages

46
Q

Where is the olfactory epithelium located

A

Olfactory nasal mucosa

47
Q

What increases the surface area of the olfactory epithelium

A

Conchae

48
Q

What is the olfactory bulb

A

It’s the part of the brain that receives direct input from the primary olfactory neurons and is an outgrowth of brain tissue from the base of the brain

49
Q

Olfactory chemoreceptors are what

A

Bipolar neurons

50
Q

What does the apical surface of the olfactory chemoreceptors have

A

4-25 immobile cilia

51
Q

What is the base of the olfactory chemoreceptor like

A

It’s a neuron

52
Q

Olfactory receptors are interspaced between what

A

Sustentacular cells

53
Q

What do sustentacular cells in olfaction do

A

They provide physical support, nourishment, electrical insulation and help detoxify chemicals

54
Q

What cells of olfaction does SARS-coV-2 infect

A

Sustentacular cells and not chemoreceptors/olfactory bulb neurons

55
Q

To infect a cell what does SARS-CoV-2 do

A

It must bind to the angiotensin converting enzyme 2 (ACE2) receptor in the cell membrane

56
Q

ACE2 is expressed by what

A

Sustentacular cells in the human olfactory epithelium

57
Q

ACE2 isn’t expressed by what

A

The olfactory sensory neurons

58
Q

What’s the life span for olfactory chemoreceptors

A

60 days

59
Q

What must the axon of each olfactory cell do

A

It must make its way to the olfactory bulb to make the proper synaptic connection

60
Q

What can harmful substances in the olfactory epithelium do

A

They can invade the sensory neurons and be transported into the CNS via the olfactory nerve

61
Q

What replaces damaged neurons in olfaction

A

Neurogenesis

62
Q

What are the 6 odor qualities

A

Floral e.g. roses
Ethereal e.g. pears
Musky e.g. perfume, aftershave
Camphor e.g. eucalyptus
Putrid e.g. rotten eggs
Pungent e.g. vinegar

63
Q

Humans recognize how many separate odors

A

10 000 ( 20% pleasant, 80% bad)

64
Q

What are of odorless gases

A

Nitrogen
Hydrogen
Ethane
Carbon monoxide
Radon
Helium

65
Q

How are molecules introduced for olfaction

A

By sniffing
By air
By diffusion from the mouth

66
Q

How does olfactory transduction work

A

-odorants bind to membrane odorant receptor proteins
-this then stimulates the G protein (Golf protein)
-the G protein then activates adenylyl cyclase
-adenylyl cyclase then forms cAMP
-cAMP then binds to a cyclic nucleotide gated cation channels
-the binding opens the channel and there is an influx of Na+ and Ca2+
-the Ca2+ then opens Ca2+ activated Cl- channels and Cl- leave the cell
-this then causes the membrane to depolarize

67
Q

what type of cells does the olfactory bulb contain

A

-mitral cells
-tufted cells
-interneurons (granule and periglomerular cells)

68
Q

what are mitral and tufted cells

A

they are the output neurons of the olfactory bulb

69
Q

what are the granules and periglomerular cells

A

they are inhibitory interneurons

70
Q

nerve fibers leading backwards from the olfactory bulb form what

A

the olfactory nerve

71
Q

what do the glomeruli in the olfactory bulb contain

A

axonal ends of the olfactory receptors and apical dendrites of the 2nd order afferent fibres

72
Q

whats the only sensation thats relayed to the cerebral cortex without passing through the thalamus

A

olfaction

73
Q

how do axons of the mitral and tufted cells move

A

they pass posteriorly through the intermediate olfactory stria and lateral olfactory stria to the olfactory cortex

74
Q

where do other fibers from the olfactory bulb project to

A
  • the entorhinal cortex, for olfactory memories
    -the frontal lobe i.e. the intermediate and medial olfactory areas , where the medial olfactory area is responsible for visceral and emotional reactions to odors
    -limbic system i.e. amygdala
75
Q

what is anosmia

A

absence of smell

76
Q

what is hyposmia

A

diminished sensitivity of smell

77
Q

what is dysosmia

A

distortion of normal smell

78
Q

what is phantosmia

A

its when there is a perception of odor in absence of an odor stimulus

79
Q

what is parosmia

A

its when there is distortion of odor perception when an odor is present

80
Q

what are causes for disorders of olfaction

A

-aging
-respiratory infections
-smoking
-growths in the nasal cavities
-head injury
-hormonal disturbances
-dental problems
-exposure to certain chemicals
-medications e.g. antibiotics and antihistamines

MBBS2/Physiology~HEAD & NECK (3 decks)

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