Cerebellar LTD Flashcards
What does LTD in the cerebellum allow for?
Co ordinated motor learning
What does LTD provide a mechanism for?
In appropriate motor signals, relayed to the cerebellum via parallel fibres are selectivity weakened through their close temporal association with climbing fibres
What does climbing fibre activation of PC at the same time as PF allow for?
It essentially ‘confirms’ that the input to the PC from the PF is inappropriate for execution of that motor sequence. This wil weaken the PF->PC connection and means on subsequent execution of the same motor plan that PC will not fire. Only the correct PC cells which alllow correct movement will fire.
What cells induce the complex spike?
Climbing fibres
What cells induce the simple spike?
Parallel fibres
The simple spike consists of current from two receptors. What are they?
AMPAR mediates current followed by mGluR mediate current
Layers of cerebellar cortex?
Molecular layer
Purkinje cell layer
Granule cell layer
White matter
Where do climbing fibres orginate and terminate?
The inferior olive and terminates on PC. 1 PC will receive inputs from only 1 CF. but 1 CF can terminate on multiple PC
What do cells from the inferior olive convey?
Error signals from sensory feedback of movement so fire when an unexpected even occurs. Propioceptive inputs and inputs from cerebral cortex
Where do mossy fibres come from?
Motor cortex and sensory afferents and contain the the information on the context of movement
Mossy fibres synapse onto…?
Granule cells
What do granule cells go?
Send axon into molecule layer and they bifurcate to form the parallel fibres. PF synapse on thousands of purkinje cells
What else does the mossy fibres and the CF synapse on?
The deep cerebellar nuclei (fastigial, dentate, interposed) provide positive inputs
What is the output to of PC’s?
Negative to deep cerebellar nuclei
What happens to the deep cerebellar nuclei on movement?
Initial excitation (CF+MF) Followed by inhibition (PC) PC cell inhibition will not occur for long due to Pf autoinhibition via Golgi cells. Therefore, deep nuclei will be inhibited again. Pattern of excitation-inhibition-excitation produces a coded message which allows movement execution.
How does LTD modulate deep cerebellar nuclei output?
If PF->PC synapses is depressed due to LTD this cell will produce a decreased rate of firing thus reduced deep nuclei inhibition on subsequent movement. Thus input to deep nuclei will vary following synaptic modulation producing a move co-ordinate movement
If the executed movement completely matched the motor plan what would happen to CF firing?
It would decrease
Who proposed a theory on how the cerebellum worked?
David Marr - the purpose of the cerebellum is to learn motor skills
How was David Marr wrong?
He thought learning occurred through potentiation of synapses not LTD
What differences are observed in the complex and simple spikes following 1Hz stimulation of CF and PF for 5 minutes
Initially both produce their respective spikes.
After traine of stimulus = no change in CF mediated PC EPSP
EPSP in PC from PF shows a depression
What receptors are responsible for the PF->PC simple spike
AMPAR (mainly GluR2+3)
mGluR. mGluR activation depends on the external of PF firing activity and glutamate release as mGluR’s are located on the periphery of the synapse. This is way later but of simple spike mGluR mediated
What receptors are important for complex spike firing?
Complex spike is forms from large EPSP superimposed with large Ca2= current.
AMPA receptors and p/q type VGCC are present
What does PF activation of mGluRs in PC cause?
Localised calcium spike
Characteristics of PF firing?
Graded responce (more fire the larger to PC EPSP)
Fast transmission mediated by AMPA
Tetanic PF simulation actives mGluR
