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chemical senses Flashcards

1
Q

where are chemoreceptors located and what do they measure?

A

in the arteries of the neck, measure co2 and o2 levels in the blood

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2
Q

how are we warned of chemical irritants?

A

nerve endings in skin/mucous membranes

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3
Q

how do we detect acidity?

A

sensory nerve endings in muscle respond to acidity

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4
Q

what is gustation?

A

taste

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5
Q

what is smell?

A

olfaction

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6
Q

how do we perceive flavour?

A

smell, taste and touch

texture and temperature

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7
Q

name some organs of taste other than the tongue

A
  • palate
  • epiglottis
  • pharynx and nasal cavity
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8
Q

palate

A

Roof of mouth separating oral and nasal cavities

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9
Q

where are taste buds present?

A

palate and epiglottis

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10
Q

epiglottis

A

Leaf shaped cartilage covering laryngeal inlet upon swallowing

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11
Q

pharynx and nasal cavity

A

odours can pass via the pharynx to the nasal cavity

-here, they are detected by olfactory receptors

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12
Q

what are papillae?

A

structures on the tongue

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13
Q

different papillae shapes?

A 
fungiform = mushroom shaped
foliate = ridged shaped
vallate = pimple shaped
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14
Q

cross section of a papillae?

A

taste buds embedded into them

  • chemically sensitive end of a taste bud is a taste pore
  • taste cells are within this, connect and synapse with the gustatory afferent axons, which transmit taste information to the brain
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15
Q

what is a taste pore?

A

chemically sensitive end of a taste bud

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16
Q

what are taste cells?

A

they are within the taste pores

they connect and synapse with the gustatory afferent axons, which transmit taste information to the brain

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17
Q

what do taste receptor cells express?

A

express different types of taste receptors

  • display different sensitivities to sweet, bitter, sour, salt
  • can be measured in AP discharge
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18
Q

five different tastes are transduced via?

A

different mechanisms

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19
Q

saltiness and sourness transduced via?

A

ion channel mechanisms

20
Q

saltiness taste transduction mechanism

A
  • Na+ passes through Na+ selective channels down its conc gradient
  • depolarises the taste cell and activates VGCCs
  • vesicular release of neurotransmitter
  • gustatory afferents activated
21
Q

what is the special Na+ selective channel and its role?

A

it is amiloride sensitive, and used to detect low concentrations of salt – insensitive to voltage and generally stays open

amiloride – diuretic drug that antagonises this paticular receptor

22
Q

sourness taste transduction mechanism

A
  • H+ passes through Na+ selective channels down its conc gradient
  • H+ also binds to and blocks K+ selective channels
  • Both these actions depolarise the taste cell, activating VGCCs
  • vesicular release of neurotransmitter
  • gustatory afferents activated
23
Q

bitterness, sweetness and umami transduced via?

A

T1 and T2 taste receptors

-T1 family and T2 family

24
Q

what are T1Rs and T2Rs?

A

They are 2 families of related taste receptor proteins

G-protein coupled receptors, specifically Gq coupled – form dimers

25
Q

bitter substances are detected by which receptors?

A

2 T2Rs

26
Q

Sweet substances are detected by?

A

one receptor – T1R2 and T1R3 proteins

27
Q

Umami substances are detected by?

A

one receptor – T1R1 and T1R3 proteins

28
Q

bitterness transduction mechanism?

A
  • Bitter tastants binds to T2 receptor - Gq coupled
  • Stimulates phospholipase C which converts PIP2 to IP3 and DAG
  • IP3 intracellularly activates a special type of Ca+ ion channel, releasing Ca2+ from the ER

Taste cell depolarised, release of ATP, gustatory afferents activated

29
Q

sweetness transduction mechanism?

A

Sweet tastants binds to dimer receptor (T1R2 and T1R3) - Gq coupled

same signal transduction mechanism as bitterness

30
Q

Why do we not confuse bitter, sweet and umami tastes if the mechanisms are the same?

A

because taste cells express either bitter, sweet or umami receptors – not all three

bitter, sweet and umami taste cells connect to different gustatory axons

31
Q

umami transduction mechanism?

A

Umami tastants bind to dimer receptor (T1R1/T1R3) - Gq coupled

same signal transduction mechanism as bitterness and sweetness occurs

32
Q

what do umami and sweetness have in common?

A

both have T1R3 protein - so the other T1R subunit determines specificity to sweetness or umami

33
Q

What is the flow of taste information to the CNS?

A

anterior tongue/posterior tongue/epiglottis –> gustatory nucleus –> ventral posterior medial nucleus –> gustatory cortex

damage at any point within these pathways, it would result in people not being able to taste certain things

34
Q

are taste and smell innate or learnt?

A

some taste/smell preferences are innate

-however experience can strongly modify our innate preferences

35
Q

what do we smell with?

A

the olfactory epithelium

36
Q

what is the the olfactory epithelium?

A

small, thin sheet of cells high up in the nasal cavity
-dendrites of olfactory cells that protrude from olfactory bulbs through the holes in our skull (cribiform plate), into the top of THE nasal passage

  1. olfactory receptor cells - site of transduction
    Each of the olfactory cells expresses a type of olfactory receptor protein
  2. supporting cells - help produce mucus
  3. basal cells - immature olfactory receptor cells – source of new olfactory receptor cells
37
Q

role of the cilia (protrusions from olfactory cells)

A

cilia are covered in a mucus layer containing sugars, variety of enzymes and odorant binding proteins

38
Q

what do the odorant binding proteins in the mucus layer do?

A

catch the smell particles and present them to the cilia of the olfactory receptor cells

39
Q

what is it important that the mucus layer contains antibodies?

A

because certain viruses/bacteria commonly enter our bodies through our nasal passage

40
Q

olfactory transduction mechanism

A
  • Odorant molecules bind to odorant receptor proteins on the cilia, activate Golf
  • AC activated, cAMP formation increased
  • cAMP-activated channels open, Na+ and Ca2+ influx
  • Ca2+ activated chloride channels, Cl- efflux
  • cell membrane depolarisation
41
Q

after depolarisation what happens to AP’s generated?

A
  • odorants generate a slow receptor potential in the cilia
  • receptor potential propagates along the dendrite and triggers a AP’s in olfactory receptor cell soma
  • propagated along the olfactory nerve axon to the brain
42
Q

where do the olfactory nerve axons go?

A

into the olfactory bulb

-signals relayed in the glomeruli and transmitted to higher regions of the brain

43
Q

explain convergence that occurs?

A

olfactory receptor cells expressing the same receptor proteins project to the same glomeruli in the olfactory bulb - convergence

44
Q

which higher regions of the brain are signals transmitted to?

A

frontal cortex - conscious perception of smell
hypothalamus and amygdala - motivational/emotional aspects of smell
hippocampus - memory

45
Q

Population coding for gustation and olfaction

A

axons in the brain responds broadly to smell, so combinations of patterns are used so they can detect which smell it is (different response patterns)

Neuro (21 decks)

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