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Neuroscience (own deck) > Chemical senses > Flashcards

Chemical senses Flashcards

1
Q

what are the functions of chemical senses?

A
  • identify food sources
  • avoid noxious substances
  • find a mate
  • mark terriories
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2
Q

how do we identify what we are tasting?

A

by the parallel processing of the gustatory system and the olfactory system
- they join together in the CNS

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3
Q

what are the 5 basic tastes?

A
  1. salty: vital electrolytes, high salt content, required for many physiological processes
  2. sour: acidity due to H+ content, avoid high acidity, avoid rotting food which could injure GI tract
  3. sweet: sugars, high sugar content, required for energy and growth
    - sweet is the first taste we experience via breastmilk
  4. bitter: diverse chemical structures, avoid bitter content, avoid toxic substances
  5. umami: amino acids, high amino acid preference, used in protein synthesis, neurotransmission
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4
Q

what are the major taste organs?

A
  • tongue
  • cheeks
  • soft palate
  • pharynx
  • epiglottis
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5
Q

what are the lingual papillae?

A
  • small projections on the dorsal side of the tongue
  • they contain 2000-5000 taste buds
  • each taste bud contains ~100 chemoreceptive taste cells
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6
Q

what is a taste pore and what does it allow?

A
  • allows sensory transduction by microvilli at the apex of taste cells
  • saliva enters the taste pore and binds to receptors on the taste cell
  • taste cell synapses to gustatory afferent neurons which sends info to CNS
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7
Q

what are the 4 types of lingual papillae?

A
  1. filiform - at centre of tongue
    - spiked
    - contain no taste buds
    - sense texture
    - most abundant
  2. foliate - towards the front
    - contain ridges
  3. fungiform - at front of tongue
    - mushroom shaped
  4. circumvallate - at back of tongue
    - large pimples
    - contain half of all taste buds
    - sense most tastes
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8
Q

what does transduction of different tastes depend on?

A

what kind of receptors the taste cells express

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9
Q

what receptors do salty taste cells express?

A

Epithelial sodium channel (ENaC)
- allows Na+ to move from the saliva into the taste cell

even if ENaC is knocked out, salty can still be detected, meaning another unknown mechanism is involved

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10
Q

what receptors do sour taste cells express?

A

OTOP1 channel:

- transduces H+ into the taste cell to cause depolarisation

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11
Q

what receptors do bitter taste cells express?

A

T2R metabotropic receptor

- causes signal transduction

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12
Q

what receptors do sweet taste cells express?

A

GPCRs:

- activate T1R2 and T1R3

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13
Q

what receptors do umami taste cells express?

A

GPCRs:

- activate T1R2 and T1R2

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14
Q

how do taste buds and taste cells vary in specificity?

A
  • taste cells respond to one type of stimuli/taste

- taste buds contain many taste cells so can respond to various stimuli/tastes

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15
Q

what are gustatory afferents?

A
  • separate cells to the taste cells
  • require neurotransmitter across synaptic cleft
  • transduction of a taste causes depolarisation via Ca2+ influx
  • influx causes vesicle fusion with membrane and release of neurotransmitter onto a primary afferent
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16
Q

what is the olfactory system?

A
  • trandsuces sense of smell
  • odorants as low as a few parts per trillion can be detected
  • human olfactory epithelium = 10cm2

dog olfactory epithelium = 170cm2
- dogs have 100x more olfactory receptor cells per cm2

17
Q

what are the components of the olfactory system?

A
  • olfactory epithelium links to the olfactory bulb
  • olfactory bulb feeds into the olfactory cortex
  • olfactory bulb contains glomeruli where olfactory receptor cells input into second order neurons which enter the brain
18
Q

how do odorants diffuse into the olfactory system?

A
  • odorants dissolve in the mucus layer to reach olfactory receptor cells
  • they then pass from epithelium to bulb
  • then into CNS through a cribiform plate
19
Q

where is the signal transduction machinery found in the olfactory system?

A
  • found within the cilia at the end of the dendrite of the olfactory sensory neuron
  • GPs form at the cilia, move up the dendrite and become APs at the axon hillock
20
Q

what is an olfactory receptor cell?

A
  • bipolar chemoreceptive cells
  • the primary afferent neuron is the axon of the olfactory receptor cell
  • the axons are thin and unmyelinated
21
Q

what is special about the olfactory receptor cells?

A

they are one of the only neurons in the body to be regularly replaced

22
Q

what are odorant receptor proteins (ORs)?

A
  • metabotropic receptors
  • humans have 350 ORs
  • olfactory receptor cells only express one OR each
  • one OR can recognise multiple odorants
  • unique combination of ORs that recognise an odorant allows us to distinguish specific smells
23
Q

how does signal transduction occur in the olfactory system?

A
  • Golf g-protein is activated when an odorant binds to an OR
  • adenylyl cyclase is activated which catalyses ATP to cAMP
  • cAMP binds to cyclic nucleotide-gated ion channels
  • allows influx of Ca2+-gated Cl- channels
  • Cl- leaves cilia, causing depolarisation due to an anion leaving the cell
24
Q

what is special about the ion concentrations in olfactory cilia?

A

they must have a high Cl- conc so it can diffuse out to depolarise the cell

25
Q

how to receptor potentials trigger APs?

A
  • large enough receptor potential will reach the threshold for AP firing
  • the more intense the stimulus, the larger the receptor potential, so AP firing rate increases
26
Q

how do olfactory receptor cells input into the glomeruli?

A
  • each glomerulus of the olfactory bulb receives input from only one type of olfactory receptor
  • the same ORs converge onto second order neurons in one glomerulus
27
Q

what does convergence of one type of ORs in each glomeruli enable?

A
  • increased sensitivity to low odorant concentrations

- there is continued sensitisation of odorants when some olfactory receptor cells are being replaced

28
Q

how do olfactory receptor cells project into the CNS?

A
  • they converge onto second order neurons which carry info from the glomeruli to the brain
  • info enters the olfactory cortex to perceive smell
29
Q

what other areas of the brain does olfactory info input into?

A
  • hippocampus - evoke memories
  • amygdala - evoke an emotional response
  • hypothalamus - sex and neuroendocrine functions
  • reticular formation in brainstem - promote visceral responses like nausea

Neuroscience (own deck) (14 decks)

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