Neural Circuits in the Olfactory System Flashcards
what are odorants
usually airborne and volatile molecules
where is smell detected
olfactory epithelium
2 methods of smell detection
- orthonasal (via nasal cavity)
- retronasal (via throat important for taste)
process of olfaction
odorant binds to receptors on the OSNs on olfactory cilia in the olfactory epithelium
OSNs depolarise and produce an AP to the OB
in the OB, OSN axons converge and synapse with other neurons in the glomeruli
receptors
once mature each neuron expresses only one gene (despite >1000 genes)
1 receptor can bind to multiple odorants
glomerular convergence
ipsilateral
ChR2 stimulation
1 group of axons responsive to light
activating only 1 OSN is sufficient for a response
why is olfaction important for survival
Dewan et al., 2013
if no receptor then anosmic (cannot perceive odours)
predators: lynx/puma
if T4 KO then cannot detect PEA (present in predator urine) approach stimulus instead of running away
types of odorants
amines
acids
aromatic phen/methoxy
pyrazines and thiazoles
OMP-ChR2 mice training
smell is recognised based on odour and timing of firing
earlier neuronal firing = stronger influence of smell
why is the first stimulus important
primary hypothesis
what do excitatory OB circuits contain
mitral cell and tufted cell
main output
mitral cell
each MC is linked to a single receptor
undergoes convergence since it receives inputs from many OSNs
OSNs form glutamatergic synapses with apical dendrites of MCs
glutamate released from olfactory nerve terminal
role of glutamate receptor antagonists on the OB
produce a smaller response
paired pulse depression = increased probability of glutamate release
what are external tufted cells
glutamatergic interneuron in the OB
acts on MC
releases NT from dendrites
TC
produces a quicker response than MC
higher somas in extended plexiform layer, more sensitive at lower concentration
provided initial response MC fills in later details
glomerular layer inhibition (local)
periglomerular cells release GABA and some DA
Short axon cells release GABA and DA
directly inhibit mitral and tufted cells
how to reduce inhibition
stronger inputs decrease PG activity via mGluR2s (in PG cells)
SACs
have long axons
perform long-range inhibition via GABA and DA
granule cell inhibition
GCs activated by M/TCs and release GABA, inhibiting neighboring M/TCs. This sharpens the odor representation by suppressing weak signals and enhancing contrasts between activated glomeruli.
granule cells
gabaergic
no axons
dendrites only
glutamate released on GC spine - causes GABA release
what do dendrodendritic synapses contain
MC secondary dendrites and GC dendrites
why is olfactory system processing faster and specialised
bypasses thalamus and projects directly to the OC
