L4 - overview of the olfactory and gustatory systems Flashcards
what is the labelled line code
neurons encode for different taste - would have dedicated channel just for sweet taste, leads to behaviour from eating sweet taste
no interlinked between channels
What is the combinational code
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
olfactory sensory transduction pathway
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
what happens in insects
instead of a G-protein receptor, they have ion channels
number of olfactory receptors in humans
300/400
number of olfactory receptors in mice and dogs
1000
number of olfactory receptors in drosophila
50
olfactory receptor specificity
each receptor is not specific to a specific odour, however they respond more to certain odours
what happens as olfactory sensory neurones mature
they narrow down to a express a singe olfactory receptor each
where do the same olfactory neuron receptors converge
on the same glomerulus
structure of drosophila olfactory receptor neurons
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
drosophila equivalent of olfactory bulb
antenna lobe
where do sensory neurones transfer information to ?
second order neurons at glomeruli - this ensure that odour specificity is maintained
what rate do sensory neurons spike at
an even rate
describe the spiking rate of the projection neurons
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
why is the spiking rate of projection neurons important
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
what does the convergence of sensory neurons onto second order neurons do
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
what is the function of local neurones / granule / glomeruli cells
they are local neurons that. live in the antenna/olfacory bulb. They transfer information between different glomeruli (lateral inter-glomerula. cross talk)
what is a gain control function of local neurons
able to respond and process stimuli that is very weak and sensitive
not sensitive to changes in strong odours
what allows this transfer function to shift from being very steep and the beginning to having a more shallow continuous response
inhibitory local neurons
what do the local inhibitory neurons inhibit
they inhibit the synapse between the ORN and the PN - in response to more stimulation of glomeruli
de-correlation
make responses of neuronal population to different odour as different as possible
what happens to correlations if know out the inhibitory neurones
they correlations between odours increase, therefore showing that the inhibitory neurons are important
what does synapsing of neurons onto a second order cell allow ?
removing noise, synaptic adaptation, lateral inhibition (gain control and de-correlation responses)
function of the piriform cortex (humans) / mushroom body (insects)
learned behaviour - associate smell with event/reward
function of the amygdala (humans) / lateral horn (insects)
innate behaviour
lateral horn neurons vs mushroom body neurons
lateral horn responds to lots of different odours
mushroom body responds to much fewer odours
how do C.elegans respond to odours
sensory neuron responds to an attractive odour which signals to another odour which inhibits turning behaviour so goes towards good odour
fly olfactory search strategy
3D space
odour comes off in odour plumes - follow plumes back to the source
smell 2 seconds in the past
what receptors does taste transduction use
metabotropic G-protein receptors and inotropic receptors
outline lateral inhibition on taste
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
