Cerebellar Microarchitecture Flashcards
Where is the cerebellum located?
At the base of the brain (looks like a small brain - cerebellum means little brain)
Where is the cerebellum most easily seen?
From a ventral view
The cerebellar cortex has ____ layers
Three
Mossy fibre input
Part of the white matter underlying the cortex
Come from many different regions of the brain and spinal cord
Synapse onto granule cells in bottom (granular) layer
Granule cells
Most numerous cells in the brain
Send their axons to top (molecular) layer, where they split into two to produce parallel fibres
These form synapses with Purkinje cells
Purkinje cells
Cell bodies in middle (Purkinje cell) layer
Sole output cells of the cerebellar cortex
Each Purkinje cell receives about 150000 parallel fibre synapses
What are the largest cells in the cerebellar cortex?
Purkinje cells
What is distinctive about the dendritic field of a Purkinje cell?
Flattened out like a fan
Climbing fibre
Each Purkinje cell also receives input from a single climbing fibre
Axons of cells in the inferior olive at base of the brainstem
Climbing fibre wraps itself around the Purkinje cell dendritic tree, forming at least 1000 synapses (all with same input signal)
Purkinje cells fire ____
Spontaneously
Firing rate of Purkinje cells
50 spikes/second
Parallel fibre input can increase this to 200 spikes/second
Complex spikes
Produced by climbing fibre input
Very reliable, whenever climbing fibre fires, PC also fires
Low frequency of firing compared with simple spikes, little effect on output
Does cerebellar damage cause paralysis?
No
It makes movements typically slow, inaccurate and uncoordinated
What is the role of the cerebellum?
To ensure that movements are carried out accurately
In order to make accurate movements…
You must have information about what you did wrong - an error signal
What do climbing fibres do?
Convey error signals
Decorrelation learning rule
A synaptic weight between parallel fibre and Purkinje cell is changed according to the correlation between the parallel-fibres signal and the error signal conveyed by the climbing fibre
Positive correlation - reduce weight
Negative correlation - increase weight
Learning stops when…
There is no longer a correlation between any parallel-fibre signal and climbing fibre signal
Why is the vestibulo-ocular reflex so important?
When the eye moves relative to the world, the image moves across the retina, blurring vision
May mean failure to detect prey or predator
When do we use the vestibulo-ocular reflex?
When we walk our head moves up and down
Reflex keeps the world stable
Flocculus
Inactivation of this region prevents adaptation of the vestibulo-ocular reflex
What else is the cerebellum thought to be involved in?
Sensory prediction
Active sensing
Emotional and cognitive processing
Disorders such as autism, dyslexia and schizophrenia
Purkinje cells in a given parasagittal strip of cortex project to…
A unique region of the deep cerebellar nuclei
This in turn projects to a unique set of neural targets
The Chip Metaphor
Strand of Purkinje cells represented by a chip
Plugged into different parts of the brain so effects are different even though they all do the same thing
