L4 - overview of the olfactory and gustatory systems

Question 1

what is the labelled line code

Answer 1

neurons encode for different taste - would have dedicated channel just for sweet taste, leads to behaviour from eating sweet taste
no interlinked between channels

Question 2

What is the combinational code

Answer 2

identity of stimulus is encoded by the entire population - different neurons activated by different stimuli
it is a combination of the extent of activation of different neurons that gives the taste

Question 3

olfactory sensory transduction pathway

Answer 3

1) odorant molecule binds to an olfactory receptor
2) activates alpha subunit of a G-protein
3) alpha subunit binds to the enzyme adenylyl cyclase
4) adenylyl cyclase turns ATP into cAMP
5) cAMP opens a cation channel which allows Na and Ca2+ to tender the cell
6) Ca2+ activates a calcium activated Cl- channel
7) Cl- exits, causing depolarisation of the sensory neuron, fires AP

Question 4

what happens in insects

Answer 4

instead of a G-protein receptor, they have ion channels

Question 5

number of olfactory receptors in humans

Answer 5

300/400

Question 6

number of olfactory receptors in mice and dogs

Answer 6

1000

Question 7

number of olfactory receptors in drosophila

Answer 7

50

Question 8

olfactory receptor specificity

Answer 8

each receptor is not specific to a specific odour, however they respond more to certain odours

Question 9

what happens as olfactory sensory neurones mature

Answer 9

they narrow down to a express a singe olfactory receptor each

Question 10

where do the same olfactory neuron receptors converge

Answer 10

on the same glomerulus

Question 11

structure of drosophila olfactory receptor neurons

Answer 11

fly has olfactory receptor neurons on antennae
the neurons that express the same receptor are scattered around the antennae however their. axons converge in the same antenna lobe

Question 12

drosophila equivalent of olfactory bulb

Answer 12

antenna lobe

Question 13

where do sensory neurones transfer information to ?

Answer 13

second order neurons at glomeruli - this ensure that odour specificity is maintained

Question 14

what rate do sensory neurons spike at

Answer 14

an even rate

Question 15

describe the spiking rate of the projection neurons

Answer 15

spikes a lot at the beginning and tails off towards the end.
This happens because the synapse between the olfactory sensory neuron and the projection neuron is rapidly adapting, this is because the presynaptic terminal runs out of readily releasable synaptic vesicles

Question 16

why is the spiking rate of projection neurons important

Answer 16

causes nerves to respond more to the start of an odour rather than a continuous response
therefore the NS dan focus on changes in odour concentrations

Question 17

what does the convergence of sensory neurons onto second order neurons do

Answer 17

reduces nouse in neural signals - averages all the sam noise

strengthens weak responses. - good if want to amplify or enhance weak signals in the environment

Question 18

what is the function of local neurones / granule / glomeruli cells

Answer 18

they are local neurons that. live in the antenna/olfacory bulb. They transfer information between different glomeruli (lateral inter-glomerula. cross talk)

Question 19

what is a gain control function of local neurons

Answer 19

able to respond and process stimuli that is very weak and sensitive
not sensitive to changes in strong odours

Question 20

what allows this transfer function to shift from being very steep and the beginning to having a more shallow continuous response

Answer 20

inhibitory local neurons

Question 21

what do the local inhibitory neurons inhibit

Answer 21

they inhibit the synapse between the ORN and the PN - in response to more stimulation of glomeruli

Question 22

de-correlation

Answer 22

make responses of neuronal population to different odour as different as possible

Question 23

what happens to correlations if know out the inhibitory neurones

Answer 23

they correlations between odours increase, therefore showing that the inhibitory neurons are important

Question 24

what does synapsing of neurons onto a second order cell allow ?

Answer 24

removing noise, synaptic adaptation, lateral inhibition (gain control and de-correlation responses)

Question 25

function of the piriform cortex (humans) / mushroom body (insects)

Answer 25

learned behaviour - associate smell with event/reward

Question 26

function of the amygdala (humans) / lateral horn (insects)

Answer 26

innate behaviour

Question 27

lateral horn neurons vs mushroom body neurons

Answer 27

lateral horn responds to lots of different odours

mushroom body responds to much fewer odours

Question 28

how do C.elegans respond to odours

Answer 28

sensory neuron responds to an attractive odour which signals to another odour which inhibits turning behaviour so goes towards good odour

Question 29

fly olfactory search strategy

Answer 29

3D space
odour comes off in odour plumes - follow plumes back to the source
smell 2 seconds in the past

Question 30

what receptors does taste transduction use

Answer 30

metabotropic G-protein receptors and inotropic receptors

Question 31

outline lateral inhibition on taste

Answer 31

tasting bitter compounds can inhibit sweet tasting compounds

1) bitter sensing neuron detects bitter compounds
2) Activates GABAergic interneuron
3) Which releases GABA onto the synaptic terminals of the sweet presynaptic neuron
4) inhibits the synaptic release of sweet sensing neuron