Motor control 3 - cerebellum Flashcards
What is the cerebellum responsible for?
The co-ordination of voluntary movements:
- control of the timing of sequences of contractions in different muscles to make a movement smooth and reliable
What are the 3 functional parts of the cerebellum?
1) Vestibulocerebellum:
- posture and balance
2) Paleocerebellum:
- control of gait
3) Neocerebellum:
- 90%; unconscious coordination of voluntary movements
What are the 2 routes by which information reaches the cerebellar cortex?
a) direct route via the pons –> mossy fibres
b) indirect route which transverses many brain areas and finally makes connections with the inferior olive nucleus –> climbing fibres
Where does input to the cerebellum come from?
Cortex:
- collaterals of CS tract neurons are sent which are a copy of signals being sent to MN’s
- major input is rediness potential which is a copy of the type of movement desired
Where does all output from the cerebellum go to?
The nucleus (dentate for the neocerebellum), relayed via the thalamus to the motor cortex.
Which cells are the only output of the cortex?
Purkinje cells
How are cerebellar circuits modified?
By experience, so that motor learning can take place. This involves setting up preferential pathways.
Describe the process of motor learning.
2 inputs to the cerebellum: mossy fibres and climbing fibres. These inputs go to the cortex and make contact with Purkinje cells. Mossy fibres activate > 1000 Purkinje cells but don’t cause them to release AP’s. Climbing fibres have a powerful excitatory 1:1 contact which causes AP discharge and inhibition of dentate nucleus. As the movement is practiced, synaptic strengthening occurs which eventually means the mossy fibre on its own can cause AP discharge from Purkinje cells. When this becomes permanent there is increased permeability to Ca and protein synthesis. A temporal code of excitation is passed to the MC.
What defects can occur in patients with cerebellar damage?
Ataxia, decomposition of movement, asynergia, dysmetria, intentional tremor, dysdiadochokinesia, posture, gait and balance deficits, and autism.
What is ataxia?
Global deficit: affects coordination, balance and speech.
What is decomposition of movement?
Instead of a movement being carried out smoothly, it is decomposed into simpler units - joint by joint. Speech also, syllable by syllable.
What is asynergia?
Lack of cooperation between agonists and antagonists - may contract together.
What effect does alcohol have on the cerebellum?
Depresses its circuits –> incoordination
How does the cerebellum project back to the cortex?
Via the ventrolateral thalamus - instructs on direction, timing and force.
Describe the motor loop through the lateral cerebellum.
Motor loop for voluntary involvement through basal ganglia and VLo undergoes ongoing refinement - via involvement of feedback loop through the pons, cerebellum, thalamus and back to cortex.
