cerebellar network

Question 1

what are the two main functional loops in the cerebellar network?

Answer 1

climbing and mossy fibres

Question 2

basic principles of the cerebellar network

Answer 2

1. cerebral cortex sends motor information to cerebellar cortex, DCN (direct route) and ION (reference of intended movement)
2. sensory input feeds into ION which detects between intended and actual movement
3. ION sends error signals to the cerebellar cortex which adjusts future motor commands (learning)
4. cerebellar cortex sends corrective instructions to DCN
5. DCN sends corrected motor output to cerebral cortex via thalamus to execute refined movement

Question 3

cerebellar afferent network: pontocerebellar

Answer 3

• 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

Question 4

cerebellar afferent network: olivocerebellar

Answer 4

• 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

Question 5

feedforward inhibition in the cerebellar network

Answer 5

1. granule recieve input from mossy and send axons to molecular layer and become parallel fibres
2. 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

Question 6

main output of the cerebellar cortex

Answer 6

GABAergic purkinje cells (inhibitory)

Question 7

what state do deep cerebellar nuclei neurons need to be to be acted on by purkinje cells?

Answer 7

active

Question 8

what is the output for deep cerebellar nuclei?

Answer 8

DCN take in inhibitory from purkinje and intergrate it with excitation of mossy and climbing to produce precise excitatory output

Question 9

what neural network forms the basic principle of the cerebellar network?

Answer 9

feedforward inhibitory network

Question 10

where does output from deep cerebellar nuclei go to?

Answer 10

1. feeds back into cerebral cortex to modulate motor output (excitatory)
2. feeds into the inferior olive (inhibitory) which also projects to the cerebellar cortex and the output is inhibitory so it still needs to drive

Question 11

ION and DCN

Answer 11

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

Question 12

what is the pacemaker circuit?

Answer 12

ION neurons have intrinsic pacemaking properties and this is regulated by inhibitory feedback from the DCN

Question 13

the neuronal machine

Answer 13

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

Question 14

cellular organisation of the cerebellum

Answer 14

1. molecular layer
2. purkinje cell layer
3. granular layer

Question 15

where do climbing fibres come from?

Answer 15

inferior olivary nucleus

Question 16

where do mossy fibres come from?

Answer 16

pontine nuclei (middle cerebellar peduncle)

Question 17

what are parallel fibres?

Answer 17

fibres that sit parallel to eachother and parallel to the surface of the cerebellar cortex in the molecular layer (huge numbers of axons)

Question 18

most important cells of the cerebellar cortex (5/8)?

Answer 18

purkinje
granule
golgi
basket
stellate

Question 19

what cerebellar cortex cells are the only excitatory ones?

Answer 19

granule

Question 20

modular organisation of the cerebellum

Answer 20

modules are repeated throughout the cerebellar cortex
the module is the unit processor

Question 21

purkinje cells

Answer 21

• large dendritic tree with a planar structure
• GABAergic inhibitory cell
• sole output of the cerebellar network
• projects to deep cerebellar nuclei

Question 22

somatotopic organisation of cortical-DCN projections:

Answer 22

vermis=fastigial
medial cortex=interposed
lateral cortex=dentate

Question 23

difference between mossy and climbing fibres

Answer 23

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.

Question 24

LTD in purkinje cells

Answer 24

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

Question 25

cellular organisation of the cerebellum

Answer 25

1. afferent neurons are excitatory (glutamatergic) and come mainly from pontine nuclei 2. they form mossy fibres 3, mossy fibres project to: - cerebellar cortex (granule cells) - axon collaterals (activate neuorns in DCN) 4. axons of granule cells bifurfacte and form parallel fibres 5. parallel fibres synapse with purkinje cells 6. purkinje cells send GABAergic signals to the DCN 7. this creates feedforward inhibition loop 8. second excitatory drive comes from ION=climbing fibres 9. excitation of climbing fibres alteras responsiveness of the parellel fibres and purkinje cells