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L2 Neural Circuits > Olfactory and Gustatory Systems > Flashcards

Olfactory and Gustatory Systems Flashcards

1
Q

Is olfaction processed by labelled line or combinatorial code?

A
  • Mostly combinatorial
  • Labelled line coding used for specialised chemicals e.g. pheromones
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2
Q

What makes olfactory sensory neurons so sensitive to stimuli?

A

The signal transduction mechanism involved G protein coupled receptors which allows for signal amplification

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3
Q

What kind of receptors are olfactory receptors in insects?

A

Ion channels

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4
Q

How many types of olfactory receptor are there per olfactory sensory neuron?

A

One

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5
Q

How many molecules does each type of olfactory receptor respond to?

A

Each olfactory receptor responds to a different subset of chemical cues

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6
Q

How are olfactory sensory neurons so specific?

A

As olfactory neurons mature the narrow down to express one type of olfactory receptor each

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7
Q

What is a glomerulus?

A

Olfactory neurons expressing the same olfactory receptor converge onto the same place in the olfactory bulb in a glomerulus structure

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8
Q

What is the equivalent of the olfactory bulb in drosophila?

A

Antennal lobe

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9
Q

What is the equivalent of olfactory sensory neurons in drosophila?

A

Olfactory receptor neurons

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10
Q

Which cells form the connections between glomeruli in mammals? (2)

A
  • Granule cells
  • Periglomerular cells
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11
Q

Which cells form the connections between glomeruli in drosophila?

A

Local neurons

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12
Q

Which cells carry information from a glomerulus to the brain in mammals? (2)

A
  • Mitral cells
  • Tufted cells
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13
Q

Which cells carry information from a glomerulus to the brain in drosophila?

A

Projection neurons

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14
Q

How is specificity maintained at the second level of the olfactory system? (2)

A
  • Olfactory sensory neurons expressing the same receptor converge onto the same glomerulus
  • The projection neuron/mitral cell/tufted cell carries information from only this glomerulus to the brain
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15
Q

What is the point of having a synapse between the sensory neurons and the 2nd order (projection) neurons? (2)

A
  • Adaptation in the synapse allows response to changing olfactory stimulation
  • Convergence onto 2nd order neurons reduces noise and strengthens weak responses
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16
Q

What is the point of having inhibitory interneurons between the glomeruli? (2)

A
  • Gain control: be able to sense changes in the stimulus even at high odour intensities by suppressing the output of the sensory neurons
  • De-correlation: strongest signals inhibit the weaker signals in order to make different odours more distinct from each other
17
Q

Where in the human brain is learned olfactory behaviour processed?

A

Piriform complex

18
Q

What is the equivalent of the piriform complex in drosophila?

A

Mushroom body

19
Q

What cells are in the mushroom body?

A

Kenyon cells

20
Q

Where in the drosophila brain is learned olfactory behaviour processed?

A

Mushroom body

21
Q

Where in the human brain is innate olfactory behaviour processed?

A

Amygdala

22
Q

What is the equivalent of the amygdala in drosophila?

A

Lateral horn

23
Q

Where in the drosophila brain is innate olfactory behaviour processed?

A

Lateral horn

24
Q

How might a brain region be silenced in an experiment?

A

Optogenetic inhibition e.g. using halorhodopsin

25
Q

What is a biased random walk? (2)

A
  • Olfactory search behaviour
  • If things are getting better, go straight (run), if things are getting worse/staying the same, turn (tumble)
26
Q

Which organisms show biased random walk behaviour? (2)

A
  • Bacteria
  • C. elegans
27
Q

How does the biased random walk behaviour work in C. elegans? (2)

A
  • Increasing odour: sensory neuron signals to inhibitory interneuron which suppresses turning
  • Decreasing odour: sensory neuron is quiet so no signalling to the inhibitory interneuron so the worm turns around
28
Q

How do flies search for olfactory stimuli? (3)

A
  • Flies upwind in the odour plume when it smells something attractive
  • If it loses the odour, waits a while before turning
  • Uses other senses to identify the source when it gets closer
29
Q

How does active sensing behaviour work? (2)

A
  • Organisms move their heads from side to side creates changes in odour intensity which are well processed by the olfactory system
  • Can sync the sniff cycle with the head movements
30
Q

How do humans sense the direction of an odour?

A

Humans use the slight differences in odour intensity between the 2 nostrils to determine the direction of an odour

31
Q

Which molecule causes a sour flavour?

A

Protons (H+)

32
Q

Which molecule causes an umami flavour?

A

Glutamate

33
Q

Which tastes trigger ion channels? (2)

A
  • Salty
  • Sour
34
Q

Which tastes trigger G protein coupled receptors? (3)

A
  • Sweet
  • Bitter
  • Umami
35
Q

What is the pathway of gustatory information from the tongue to the brain? (3)

A
  • Cranial nerves carry gustatory signals from the tongue to the solitary nucleus of the brainstem
  • Some signals are passed from there to the hypothalamus and amygdala
  • The rest of the signals are sent to the VPM of the thalamus and then to the insula and parietal cortex
36
Q

What is the VPM?

A

Ventral Posterior Medial Nucleus of the thalamus

37
Q

How does lateral inhibition work in the gustatory system? (2)

A
  • Bitter sensing neurons activate GABAergic interneurons which inhibit signal release from sweet sensing neurons
  • Mechanism to stop you eating poison by emphasising the bitter taste over the sweet taste
38
Q

How does the circuitry for innate behaviour and learning behaviour differ? (3)

A
  • Innate behaviour needs to categorise odours but learning behaviour needs to discriminate between new odours
  • Innate behaviour odour coding is dense (lots of neurons active) but needs to be sparse for learning
  • Connectivity is stereotypic for innate behaviour so the same neurons are active for the same odour every time but for learning the connectivity is random and not developmentally pre-specified

L2 Neural Circuits (13 decks)

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