cerebellar network Flashcards
what are the two main functional loops in the cerebellar network?
climbing and mossy fibres
role of the cerebral cortex in the cerebellar network
excitatory motor output-version of this will go into the cerebellar cortex (copy of intention), this is glutamatergic
main output of the cerebellar cortex
GABAergic purkinje cells
what state do deep cerebellar nuclei neurons need to be to be acted on by purkinje cells?
active
what is the output for deep cerebellar nuclei?
excitatory neurons which are only active when they are recieving an input
what neural network forms the basic principle of the cerebellar network?
feedforward inhibitory network
how does the 3rd neuron in the feedfoward inhibition network become active?
collateral from 1st excitatory neuron makes cell 3 active at same time as inhbitory cell 2 but is also acted on by cell 2 which reduces its effect
where does output from deep cerebellar nuclei go to?
- feeds back into cerebral cortex to modulate motor output (excitatory)
- feeds into the inferior olive (inhibitory) which also projects to the cerebellar cortex and the output is inhibitory so it still needs to drive
inferior olive and deep cerebellar nuclei
IO excitatory drives cerebellar nuclei to inhibit deep cerebellar nuclei
this reduced activity in the olive as it will feed back
this puts a break on input
olivary cells are driven by excitatory sensory input but this is reduced
reduced excitation=reduced output=reduced inhibitory=increased inhibitory output from deep cerebellar nuclei
what is the pacemaker circuit?
deep cerebellar nuclei to inferior olive loop
the neuronal machine
cerebellum-little brain, holds ~50% of all neurons in 10% of the brain volume
has an extremely regular structure
this regularity in structure is key to its function
cellular organisation of the cerebellum
- molecular layer
- purkinje cell layer
- granular layer
where do climbing fibres come from?
olivary nucleus
where do mossy fibres come from?
pontine nuclei (middle cerebellar peduncle)
what are parallel fibres?
fibres that sit parallel to eachother and parallel to the surface of the cerebellar cortex in the molecular layer (huge numbers of axons)
most important cells of the cerebellar cortex (8)
purkinje
granule
golgi
basket
stellate
what cerebellar cortex cells are the only excitatory ones?
granule
modular organisation of the cerebellum
modules are repeated throughout the cerebellar cortex
the module is the unit processor
purkinje cells
- large dendritic tree with a planar structure
- GABAergic inhibitory cell
- sole output of the cerebellar network
- projects to deep cerebellar nuclei
somatotopic organisation of cortical-DCN projections:
vermis=fastigial
medial cortex=interposed
lateral cortex=dentate
step 1 of the unit processor
afferent neurons are excitatory (glutamatergic);
most originate from the pontine nuclei (cortical input) but also reticular nuclei and vestibular nuclei
these form the mossy fibres
step 2 of the unit processor
mossy fibres project to both the cerebellar cortex where they synapse with granule cells (excitatory)
step 3 of the unit processor
axon collaterals activate neurons in the deep cerebellar nuclei and this provides a continuous drive for input neurons
step 4 of the unit processor
axons of the granule cells rise through the molecular layer, bifurcate and project parallel to the surface of the brain – form the parallel fibres
step 5 of the unit processor
parallel fibres form synapses with purkinje cells which send inhibitory (GABAergic) axons to inhibit the DCN
step 6 of the unit processor
purkinje cells inhibits the DCN forming a feed forward inhibitory loop
step 7 of the unit processor
a second excitatory input comes form the the inferior olive- the climbing fibre
step 8 of the unit processor
a single axon branches through the dendritic tree forming hundreds of excitatory synapses
step 9 of the unit processor
excitation of the climbing fibre can alter the responsiveness of the PC to pf input
difference between mossy and climbing fibres
mossy fibre=intention
climbing fibre=action
firing together induced long term depression in purkinje
LTD in purkinje cells results in…
inhibitory output going to DCN weakens
