Lecture 5 - chemical senses Flashcards
olfactory sensory transduction
- 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
why are these amplification systems useful?
they increase the sensitivity of the neurons of even dilute odours
olfactory receptors in mammals vs insects
in mammals they are GPCR and in insects they are ion channels
where do all axons go to
glomerulus. sensory neurons with different receptors go to different glomeruli
what is the insect equivalent of an olfactory bulb?
antennal lobe
local neurons
these carry information between the glomeruli these are granule cells and periglomerular cells
second order neurons
receive the information from each glomerulus these are mitral cells and tufted cells
how is odour specificity carried through?
receptor-specific matching of sensory neurons to second-order neurons
what does the first relay synapse do?
transforms the odour code between sensory neurons and second-order neurons
synaptic adaptation
- 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
converging sensory neurons onto second-order neurons
- 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
the two functions of lateral cross-talk
gain control and de-correlation
mechanism of gain control
for systems to be sensitive to different intensities is by the interneurons
weak odour on a graph (gain control)
with a weak odour the second-order neurons respond a lot. the plateau of the graph is where projection neurons are saturated
strong odour on a graph (gain control)
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