cerebellar network Flashcards
what are the two main functional loops in the cerebellar network?
climbing and mossy fibres
basic principles of the cerebellar network
- cerebral cortex sends motor information to cerebellar cortex, DCN (direct route) and ION (reference of intended movement)
- sensory input feeds into ION which detects between intended and actual movement
- ION sends error signals to the cerebellar cortex which adjusts future motor commands (learning)
- cerebellar cortex sends corrective instructions to DCN
- DCN sends corrected motor output to cerebral cortex via thalamus to execute refined movement
cerebellar afferent network: pontocerebellar
- carries copies of motor commands (also called efference copies or corollary discharge).
- provides contextual and planned movement information to the cerebellum
- pontine, middle peduncle, synapse on granule
cerebellar afferent network: olivocerebellar
- conveys error signals—differences between intended and actual movement (sensory feedback mismatch).
- often activated by unexpected outcomes or mismatches
- ION, inferior peduncle, synapse on purkinje
feedforward inhibition in the cerebellar network
- granule recieve input from mossy and send axons to molecular layer and become parallel fibres
- parallel fibres synapse onto purkinje (excitatory input) and inhibitory interneurons (basket and stellate)
TF excitatory input activates purkinje directly however it also activates inhibitory interneurons that suppress purkinje cells
this sharpens timing of purkinje output and prevents excessive excitation
main output of the cerebellar cortex
GABAergic purkinje cells (inhibitory)
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?
DCN take in inhibitory from purkinje and intergrate it with excitation of mossy and climbing to produce precise excitatory output
what neural network forms the basic principle of the cerebellar network?
feedforward inhibitory network
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
ION and DCN
ION sends excitatory collaterals to the DCN
DCN send inhibitory projections back to the ION = negative feedback loop
this loop regulates timing and synchronry of olivary activity and helps fine tune error signals sent to cerebellum
what is the pacemaker circuit?
ION neurons have intrinsic pacemaking properties and this is regulated by inhibitory feedback from the DCN
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?
inferior 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 (5/8)?
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
difference between mossy and climbing fibres
mossy fibers (pontocerebellar) bring in the planned motor action
climbing fibers (olivocerebellar) bring in feedback about whether the action was successful or not
if there’s a mismatch (an error), climbing fibers trigger complex spikes in purkinje cells.
LTD in purkinje cells
complex spikes triggered by climbing fibres induce LTD of synapses that were active at the same time as the error signal
this inhibits purkinje output to DCN
cellular organisation of the cerebellum
- afferent neurons are excitatory (glutamatergic) and come mainly from pontine nuclei
- they form mossy fibres
3, mossy fibres project to:
- cerebellar cortex (granule cells)
- axon collaterals (activate neuorns in DCN) - axons of granule cells bifurfacte and form parallel fibres
- parallel fibres synapse with purkinje cells
- purkinje cells send GABAergic signals to the DCN
- this creates feedforward inhibition loop
- second excitatory drive comes from ION=climbing fibres
- excitation of climbing fibres alteras responsiveness of the parellel fibres and purkinje cells
