Lecture 5 - chemical senses

Question 1

olfactory sensory transduction

Answer 1

• binding of an odorant molecule triggers adenylyl cyclase
• cAMP activates ion channels and calcium gated cloride channels
• at every step in the pathway amplifies the signal more

Question 2

why are these amplification systems useful?

Answer 2

they increase the sensitivity of the neurons of even dilute odours

Question 3

olfactory receptors in mammals vs insects

Answer 3

in mammals they are GPCR and in insects they are ion channels

Question 4

where do all axons go to

Answer 4

glomerulus. sensory neurons with different receptors go to different glomeruli

Question 5

what is the insect equivalent of an olfactory bulb?

Answer 5

antennal lobe

Question 6

local neurons

Answer 6

these carry information between the glomeruli these are granule cells and periglomerular cells

Question 7

second order neurons

Answer 7

receive the information from each glomerulus these are mitral cells and tufted cells

Question 8

how is odour specificity carried through?

Answer 8

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

Question 9

what does the first relay synapse do?

Answer 9

transforms the odour code between sensory neurons and second-order neurons

Question 10

synaptic adaptation

Answer 10

• first there is adaptation of synapse to emphasise the start of the odour
• sensory neurons respond when there is an odour
• projection neurons adapt to not fire as much and runs out of vesicles

Question 11

converging sensory neurons onto second-order neurons

Answer 11

• sensory neurons converge on one spot and this reduces the noise
• second order neurons listen to many sensory neurons
• projection neurons response is a sharp spike response to help detect weak odours

Question 12

the two functions of lateral cross-talk

Answer 12

gain control and de-correlation

Question 13

mechanism of gain control

Answer 13

for systems to be sensitive to different intensities is by the interneurons

Question 14

weak odour on a graph (gain control)

Answer 14

with a weak odour the second-order neurons respond a lot. the plateau of the graph is where projection neurons are saturated

Question 15

strong odour on a graph (gain control)

Answer 15

with a strong odour it activates multiple glomeruli with lateral cross talk between them
recruit inhibiting interneurons and pushes the curve over to the right and less steep at the beginning

Question 16

de-correlation

Answer 16

decorrelate the odour responses and make the odours more widely separated
for each pair of odours, can calculate the similarity between the responses of different odours

Question 17

mechanism of decorrelation

Answer 17

• knock out the lateral inhibiting neurons, the odour responses become more similar
• stronger channels inhibit the weaker neurons
• makes the odour responses more distinctive

Question 18

which area associates a particular odour?

Answer 18

piriform cortex

Question 19

which area is for more innate behaviour?

Answer 19

amygdala in mammals and lateral horn for insects

Question 20

where does learned behaviour happen for insects?

Answer 20

in the Kenyon cells in mushroom body

Question 21

how to reduce the response to an odour in the amygdala?

Answer 21

express the inhibiter in the amygdala and shine a light

Question 22

learning circuitry

Answer 22

need to discriminate multiple odours in the world and has sparse activity

Question 23

innate circuity

Answer 23

only way certain neurons to respond and has dense activity

Question 24

olfactory search behaviour

Answer 24

• if things get better with an increased concentration of nutrient, go towards and turn less
• chemical system detects the nutrient to keep going but if not it changes directions

Question 25

active sensing search strategy

Answer 25

- behaviour allows the animal to actively sense the environment to fit well with how the olfactory system processes information - moving head back and forth actively changing the concentration of the odour

Question 26

taste transduction

Answer 26

- uses metabotropic and ionotropic receptors and amplifies signals - chemical cues are GPCR that triggers enzyme and second messengers - salt taste is iontropic

Question 27

where do cranial nerves go?

Answer 27

go from the tongue to the solitary nucleus in the brainstem

Question 28

where is information from the thalamus relayed into?

Answer 28

relayed into the insula and parietal cortex

Question 29

what happens when tasting bitter and sweet at the same time?

Answer 29

the bitter tatste does lateral inhibiton of the sweet neurons and surpresses the synpatic release

Question 30

stimulating sensation of tastes

Answer 30

stimulate sensation of the bitter taste with a light and triggers artificial perception of taste