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Neuroscience > Olfaction and Taste > Flashcards

Olfaction and Taste Flashcards

1
Q

what are smell and taste coupled to?

A

memory

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2
Q

what is the function of smell and taste?

A
  • guide to the quality of food
  • mate selection (pheromones)
  • danger and poison
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3
Q

what is olfaction?

A
  • smell
  • detection of chemicals at a distance
  • optimised for combinatorial detection for vast numbers of odorants
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4
Q

what is gustation?

A
  • taste
  • requires direct contact with relevent chemical
  • organised to categorise tastants into non-overlapping categories
  • sweet, bitter and sour, salty and umami
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5
Q

what is flavour?

A
  • fusion of taste and odour, also somatosensory

- odour, texture and warmth

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6
Q

what are the different taste qualities?

A
  • bitter (GPCRs), detecting poisons
  • sweet (GPCRs), sugars and carbohydrates
  • sour (ion channels?), organic acids, food is going off
  • salty (ion channels), sodium
  • umami (GPCRs), L-amino acids, nucleotides
  • fats (unknown) might be a function of texture
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7
Q

how often are taste receptor cells regenerated?

A
  • regenerated thoughout life by stem cells

- life of a taste cell is around 2 weeks

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8
Q

why do taste receptor cells need to be regenerated?

A

they are exposed on the surface, getting damaged so have to be replaced

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9
Q

what is the structure of a taste bud?

A
  • has up to 100 polarised neuroepithelial cells
  • form columnar islands in the oral cavity
  • tips of the cells directly contact apical surface
  • described by their shape and proteins (types I,II,II,IV)
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10
Q

what is the function of a taste bud?

A
  • chemicals interact with the cells and signalling occurs

- connect to afferent neurons

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11
Q

what are the functions of type I cells?

A
  • express ion channels such as ENaC which transports Na+ ions into the cell
  • ROMK, extrude K+ ions out of the cell
  • detects salty flavours
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12
Q

what are the functions of type II cells?

A
  • detect sweet, bitter and umami
  • conducts response on which GPCR they express
  • each type II will only express one type of receptor
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13
Q

what is the process of a type II cell?

A
  • ligand binds to GPCR
  • activates a G protein
  • activates PLC beta2 breaking down PIP2 into DAG and IP3
  • IP3 will activate calcium stores
  • causes flux of calcium which activates 2 channels: TRP and Panx1
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14
Q

what is the role of TRP channel in type II cell signalling?

A
  • TRPM5 channel

- causes Na+ to flow into the cell

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15
Q

what is the role of Panx1 in type II cell signalling?

A

releases ATP

ATP acts as a neurotransmitter

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16
Q

what is the function of type III cells?

A

they detect sour but not sure how

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17
Q

how is thought that type III cells might work?

A
  • organic acids permeate through the plasma membrane, dissocaite and acidify the cytoplasm
  • intracellular H+ blocks a proton sensitive K+ channel to depolarise the membrane and release the neurotransmitter
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18
Q

what TRP channels are though to be involved in type III cells?

A

PKD2L1 and PKDIL3

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19
Q

what do taste buds sort out?

A
  • find the predominant taste

- tastants are complex and major tastes need to be discerned

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20
Q

how is cross talk between the cell types useful?

A

generate a signal giving an indication of the predominant taste in the tastant
- neurons make contact with type II and type III but how they communicate is not understood

21
Q

what GPCRs are sweet and umami detect by?

A

heterodimers that share a common subunit for T1R3

22
Q

what is bitter detected by?

A

T2R receptors

23
Q

what is sour detected by (potentially)?

A

PKD2L1

24
Q

why is it important that T1Rs are low affinity for their ligand?

A
  • saturation is not easily reached
  • has high caloric intake
  • ligand is bouncing on and off (constantly firing)
  • eg you eat chocolate and it will still taste sweet
25
Q

why is it important that T2Rs have high affinity?

A
  • considered dangerous so you want a strong response
26
Q

what is information from type I, II and III cells carried by?

A

afferent neurons to the CNS

27
Q

what are the two models for coding?

A

labelled line and across fibre

28
Q

what is labelled line?

A
  • following the connections from the primary sensory cell gives a clear line to the CNS processing centre
  • idea that you have dedicated wiring for each sense and the signal follows the wiring
29
Q

what is across fibre?

A
  • cross talk

- integration of the signal between a number of primary sensory neurons

30
Q

what do mammalian nasal passages allow?

A

allow air to recirculate due to the shaping of turbinate bones
(get the resampling of air)

31
Q

what do odours carried in the air bind to?

A
  • the olfactory epithelium
32
Q

what happens when odours bind to the olfactory epithelium?

A

-activate the olfactor neurons sending a signal through the cribriform plate to the olfactory bulb

33
Q

what detects pheromones?

A

vomeronasal organ

34
Q

where do olfactory neurons project too?

A

into the mucus of olfactory cuff

35
Q

how many types of receptor does each olfactory sensroy neuron (OSN) express?

A

one

36
Q

how long do olfactory neurons live for?

A
  • live for around 90days

- renewed via stem cell development

37
Q

how are olfactory neurons organised?

A
  • neurons expressing a given OR are orgnaised into broad zones along the dorsal-ventral axis of the olfactory epithelium
  • converge to a common glomerulus at corresponding dorsal-ventral zones in the olfactor bulb
38
Q

what innovation does a glomerulus recieve?

A
  • recieves innovation from neurons expressing a single odorant receptor
39
Q

what is the process of an odorant receptor binding a ligand?

A
  • receptor binds an odorant
  • activates a G proten (G alpha olf)
  • activates adenylyl cyclase
  • ATP –> cAMP
  • cAMP binds to a cyclic nucleotide gated channel allowing Ca2+/Na+ to flow
  • action potential activates pKA
40
Q

how does pKA work in the process of odorant receptor activation?

A
  • pKA becomes activated
  • activates transcription CREB
  • activates a pathway guiding neuronal growth and connection
41
Q

how many repeptors can an odorant bind?

A
  • can bind more than one receptor but will produce signals of differing magnitude in different olfactory cells
  • some are finely tuned some are more broad
42
Q

how is the identity of the odorant determined?

A

the pattern of neuronal activity informs the CNS of the molecular identity of the odorant

43
Q

how is sense of smell mediated in insects?

A

by the antenna and maxillary palp

44
Q

how is taste mediated in insects?

A
  • through pits in the proboscis
  • taste receptors in the feet sense food
  • positive signal is relayed to mediate ‘proboscis extension reflex’
45
Q

where do insect olfactory sensory dendrites project?

A
  • up into the antennal hairs of the insect

- sensilla have pores allowing passage of air to make contact with fluid inside

46
Q

what happens in the sesillum lymph?

A
  • odorants bind to odorant binding proteins (OBPs)
  • then bind to olfactory receptors (ORs)
  • generate an action potential as ligand and cycle nucleotdie gated ion channels
47
Q

what is the strutcure of odorant receptors in insects?

A
  • they are heterodimers
  • one of the subunits is obligate OR83b
  • there is one receptor heterodimer expressed in each olfactory neuron
48
Q

what happens if insects are mutants for OR38b?

A

they are alosmic - have no sense of smell

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