The cerebellum and motor learning

Question 1

What is the role of the cerebellum?

Answer 1

Maintenance of balance and posture
Coordination of voluntary movements
Motor learning
Cognitive functions

Question 2

Which level of the motor control hierarchy is the cerebellum involved in?

Answer 2

Middle level
Tactics
Along with the motor cortex

Question 3

What is another name to describe the cerebellum?

Answer 3

The great comparator

Question 4

Describe what the cerebellum does to perform its function

Answer 4

Compares what you intend to happen to what is actually happening
Sends out a correction signal involving planning, initiation and execution for an event you intend on occuring.

Question 5

Describe the location of the cerebellum

Answer 5

Posterior to 4th ventricle
Posterior to brainstem
Inferior to occipital lobe

Question 6

Describe the structure of the cerebellum

Answer 6

3 lobes - anterior, posterior, flocculonodular
Arbor vitae
Cerebellar nucleus
Lobes separated by vermis

Question 7

List the functional subdivisions of the cerebellum

Answer 7

Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum

Question 8

How many somatotopic maps of the body are found in the spinocerebellum?

Answer 8

2

Question 9

Which nuclei are found in the lobes of the cerebellum?

Answer 9

Fastigial
Interposed
Dentate

Question 10

Describe the cerebellar outputs of the fastigial nucleus

Answer 10

Medial descending systems - motor execution

Question 11

Describe the cerebellar outputs of the interposed nucleus

Answer 11

Lateral descending systems - motor execution

Question 12

Describe the cerebellar outputs of the dentate nucleus

Answer 12

areas 4 and 6 - motor planning

Question 13

Describe the cerebellar outputs of the vestibular nucleus

Answer 13

balance and eye movements

Question 14

What is the importance of the spinocerebellum?

Answer 14

Control of posture and muscle tone

Question 15

Give some examples of effects of lesions to cerebrocerebellum pathway

Answer 15

Dysmetria
Dysnergia
Dysdiadochokinesia
Intentional tremor
Dysarthria

Question 16

What is dysmetria?

Answer 16

Movement is not stopped in time

Question 17

What is dysnergia?

Answer 17

Decomposition of complex movements

Question 18

What is dysdiadochokinesia?

Answer 18

Reduced ability to perform rapidly alternating movements

Question 19

What is an intentional tremor?

Answer 19

Tremor arising when trying to perform a goal directed movement

Question 20

What is dysarthria?

Answer 20

Articulation incoordination
Incoordination in respiratory muscles, muscles of the layrnx etc.
Uneven speech strength and velocity

Question 21

Give the effect to lesions in the vestibulocerebellar pathway

Answer 21

Nystagmus - involuntary, rhythmic, repeated oscillations of one or both eyes in any or all directions of view.
Movement of the eyes maximises the ability to focus the eyes on one point (fixation)

Question 22

Give an effect of a lesion to the spinocerebellar pathway

Answer 22

Gait ataxia (unsteadiness when walking) and disturbance of limb tone (hypotonia) and posture

Question 23

Describe cerebellar inputs and outputs

Answer 23

Inputs:

• Mossy fibres from spinal cord and brainstem
• Climbing fibres from inferior olivary nucleus

Outputs:
- Deep cerebellar nuclei to thalami, vestibular nuclei and red nucleus

Question 24

What is the output of purkinje cells?

Answer 24

Deep cerebellar nuclei

Question 25

How many climbing fibres are there per purkinje cell?

Answer 25

1 but many synapses (divergence)

Question 26

Describe the relationship between parallel fibres and purkinje cells

Answer 26

1 Parallel fibre per purkinje cell but one or few synapses on each (convergence)

Question 27

List the layers of neuron classes

Answer 27

Molecular layer Purkinje cell layer Granule cell layer

Question 28

Describe feedback during motor learning

Answer 28

Motor cortex and red nucleus generate signals via the corticopontinecerebellar tract. Proprioceptive feedback from muscles and joints via the spinocerebellum and the vestibulocerebellum pathways. Actual response is compared with desired response via the cerebrocerebellum inputs from the supplementary motor cortex and the primary motor cortex to produce error signals.

Question 29

Describe a feedback loop

Answer 29

Error signal is the difference between desired input and the output. The feedback comes from the output.

Question 30

Describe the feedforward loop

Answer 30

Movements that are too fast to be corrected by feedback are executed using predictions of their outcome based on experiences. Crucial for learning new motor skills e.g riding a bicycle, playing tennis, driving. Advanced informaiton is used to generate the desired output and this fedforward to generate the output. Waiting for a feedback from the output would be too low. The error signals derive mainly from sensory information e.g direction of ball whist playing tennis, error in playing a musical instrument will sound wrong. The error signals are sent via the inferior olivary nucleus which then lead onto the climbing fibres

Question 31

Describe the complex spikes of the cerebellum

Answer 31

The combination of the climbing fibres (error signal/complex spikes, background firing rate is 20-50Hz) and the mossy fibres (desired signal/simple spikes, Background firing rate 50-100Hz) will alter the output of the purkinje cell till you get a desired response. As a task is being learned, there are lots of complex and simple spikes. As complex spikes decrease, it changes the connections between the parallel fibres and the purkinje cells resulting in a reduction in effect from the simple spikes. The long-term reduction in activation of the purkinje cells to a given task is an example of plasticity.

Question 32

List some genetic causes of cerebellar dysfunction

Answer 32

Inherited (rare) Frederich’s ataxia Spinocerebellar degeneration (Ataxia may occur if major connections disrupted) Ataxia-telengiectasia Von Hippel Lindau

Question 33

Give some causes of acquired symmetrical ataxia

Answer 33

``` Alcohol Metabolic (B12/Thyroid/Coeliac) Drugs (eg phenytoin) Degenerative (familial, MSA) Immune (paraneoplastic) ```

Question 34

Describe the vascular anatomy of the cerebellum

Answer 34

``` Branches of basilar artery: Vertebral SCA AICA PICA ```

Question 35

When is ataxia more profound?

Answer 35

if cerebellar nuclei, brainstem nuclei or white matter tracts involved (MS) than cerebellar cortex as some degree of plasticity