olfaction

Question 1

What is olfaction?

Answer 1

A multidimensional coding sequences – cannot be measured along a fixed dimension

Question 2

What is labelled line in olfaction?

Answer 2

One dedicated channel to process one smell ‘taste’

Receptor input – labelled line – line decoder output

Question 3

What is combinatorial code?

Answer 3

Identity not dedicated to one taste but coded by entire population.
Receptor input – pattern code- pattern decoder output

Question 4

What amplifies sensory signals in olfaction?

Answer 4

Second messengers amplify sensory signals

Allows action potentials to fire and stimulus to be detected.

Question 5

Describe the olfactory signal transduction

Answer 5

• Oderants
• Bind to membrane odorant receptor proteins
• Stimulate G-protein Golfs
• Activate adenylyl cyclase
• Form cAMP
• Bind cAMP to a cyclic nucleotide-gated ion cation channel.
• Open cation channels and allows influx of Na and Ca
• Open Ca activated Cl channels
• Cause current flow and membrane depolarisation (receptor potential)

Question 6

What does each neuron express in olfaction? What happens as olfactory sensory neurons mature?

Answer 6

A single type of receptor. and They narrow down to express a single olfactory receptor each.

Question 7

In olfaction, what converge on the same glomerulus?

Answer 7

Olfactory sensory neurons expressing same receptor

Question 8

What is the olfactory bulb equivalent called in drosophila?

Answer 8

Antennal lobe

Question 9

Where do sensory neurons transfer their information to?

Answer 9

Second-order neurons at glomeruli

Question 10

What ensures odour specificity is carried through?

Answer 10

Receptor-specific matching of sensory neurons to second-order neurons

Question 11

State was is involved in sensory neuron transfer information in mammals

State was is involved in sensory neuron transfer information in Drosophila

Answer 11

mammals
Olfactory sensory neurons
Mitral cells, tufted cells

Drosophila
Olfactory receptor neurons
Projection neurons

Question 12

what transforms the odor code?

Where is it in olfaction?

Answer 12

The first relay synapse

Between sensory neurons and second-order neurons.

Question 13

What does the synapse do over time? what does this allow

Answer 13

It weakens

Allows nervous to respond better to start of odor rather than continuously

Question 14

What does converging sensory neurons (expressed same receptor) onto same second-order neurons enable?

Answer 14

• Reduces noise

- Strengthens weak responses – allows to enhance in a weak environment

Question 15

What are the functions of lateral cross talk in lateral inter-glomerulus?

Answer 15

Gain control: be sensitive to both very weak and very strong odour
De-correlation: makes responses of neuronal population to different odours as different as possible

Question 16

What do different areas of the brain regulate?

Answer 16

Different kinds of high olfactory behaviour – learned vs innate

Learned behavior: piriform cortex = mushroom body (Kenyon cells)

Innate behavior: Amygdala = lateral horn

Question 17

Explain an experiment which proves the function of the lateral horn

Answer 17

Fruit flies normally avoid laying eggs on food that smells of toxic microbes
But if you silence this lateral horn region, they fail to avoid laying eggs on the toxic food

Question 18

the differences between innate and learned olfaction

Answer 18

purpose
Innate: categories
Learning: discriminate

activity
Innate: dense
Learning: sparse

odours
Innate: certain preferred
Learning: arbitrary

connectivity
Innate: stereotyped
Learning: random