Motor Control 2

Question 1

What is the cerebellum responsible for?

Answer 1

The co-ordination of voluntary movements

Question 2

Define co-ordination

Answer 2

Control of the timing of sequences of contractions in different muscles to make a movement smooth and reliable

Question 3

What makes up the outer part of the cerebellum?

Answer 3

A highy convoluted grey matter cerebellar cortex

Question 4

What makes up the layer beneath the cerebellar cortex of grey matter?

Answer 4

White matter containing axons going to and from the cortex?

Question 5

Where are the deep cerebellar nuclei?

Answer 5

Deep within the white matter of the cerebellum

Question 6

What are the three functional areas of the cerebellum?

Answer 6

Archicerebellum (Vestibulocerebellum)

Paleocerebellum

Neocerebellum

Question 7

What is the function of the archicerebellum?

Answer 7

Concerned with posture and balance, with major input form the vestibular system

Question 8

What is the paleocerebellum?

Answer 8

More important in 4 legged animals, has control of gait in humans

Question 9

What is the function of the neocerebellum?

Answer 9

Makes up 90% of cerebellum, responsible for unconscious co-ordianation of voluntary movements

Question 10

Where does input to the cerebellum reach first?

Answer 10

All of it goes to the cortex/cerebellar hemisphere

Question 11

Where does output come from in the cerebellum?

Answer 11

The dentate nucleus

Question 12

Where does output from the dentate nucleus in the cerebellum go?

Answer 12

It is relayed but eh thalamus to the MC

Question 13

How can information reach the cerebellar cortex?

Answer 13

In two ways. Firstly, a direct route via the pons of the brainstem
Or, an indirect route which traverses several brain areas and finally makes connections in the inferior olive nucleus in the brainstem

Question 14

What is the name of the fibres running from the pons to the cerebellar cortex? (direct route)

Answer 14

Mossy fibres

Question 15

What is the name of the fibres running from the inferior olive to the cerebellar cortex? (indirect route)

Answer 15

Climbing fibres

Question 16

Do CS tract neuron collaterals pass to the cerebellum?

Answer 16

Yes, passing copies of signals being sent to the motoneurons

Question 17

What is the major electrical input to the cerebellum with regard to movement?

Answer 17

The readiness potential

Question 18

How can motor learning take place in the cerebellum?

Answer 18

Via the circuits that are contained within it - developing preferential pathways

Question 19

What is the function of the circuits within the cerebellum?

Answer 19

To enable the precise timing of movements to be calculates

Question 20

Does the cerebellum carry a motor homunculus?

Answer 20

Yes

Question 21

What fibres form the output from the cerebellum?

Answer 21

Purkinje cells

Question 22

What is the effect of mossy fibres on the purkinje cells? Where do the mossy fibres come from?

Answer 22

They act on around 1000 cells per mossy fibre, slightly raising the level of excitation but not enough to fire APs. They are responsible for the readiness potential

Question 23

What is the effect of climbing fibres on the pukinje cells? Where do they come from?

Answer 23

The make powerful excitatory contact with the cells on a 1:1 basis. They do cause APs to fire, inhibiting the dentate nucleus. This creates the binary like signal that will be mentioned further

Question 24

What is the principle of motor learning with respect to climbing fibres?

Answer 24

The learning process is about finding the right climbing fibre over time

Question 25

What occurs as a result of mossy and climbing fibre action to the purkinje cells?

Answer 25

Synaptic strengthening - this means that eventually only mossy fibre input is needed to cause APs to discharge from the purkinje cells
Movement becomes automatic and the climbing fibres are no longer needed for that specific movement. The synaptic strengthening is permanent, and involves increased calcium permeability and protein synthesis

The mossy fibre activity creates a binary type pattern of excitation signal, constant but with a small gap between each purkinje fibre excitation. The strengthened purkinje fibres will discharge an AP in temporal pattern. The inhibitory action of the nucleus of these APs punches gaps of inhibition into the stream of mossy excitations. This forms a temporal code which can be passed to the MC to produce a smooth and reliable movement

Question 26

What is ataxia?

Answer 26

Global deficit - incoordination. Specific effects depend on the area of the cerebellum damaged

Question 27

Describe decomposition of movement that can occur in patients with cerebellar damage?

Answer 27

Instead of movement signals being formed smoothly via the combination of mossy and climbing fibres in a healthy individual, they decompose into simpler units e.g. joint by joint

Question 28

What effect does decomposition of movement have on speech?

Answer 28

Dysarthria or staccato speech - no aphasia but mechanical aspects of speech are slow, impaired and syllable by syllable

Question 29

What is asynergia?

Answer 29

Lack of cooperation between agonists and antagonists, may contract together

Question 30

What is dysmetria?

Answer 30

‘Past-pointing’. goal directed movements lack accuracy, point past, short or to the side of the target

Question 31

What is an intentional tremor?

Answer 31

Occurs during movement and particularly towards the end, NOT at rest

Question 32

What is dysdiachokinesia?

Answer 32

An inability to make rapidly alternating opposite movements

Question 33

Describe posture, gait and balance deficits? Information from what system is of particular relevance?

Answer 33

Patients adopt a wide stance with a tendency to fall over (drunken sailor’s gait). Associated with the vestibular system