The cerebellum and motor learning Flashcards
1
Q
Role of the cerebellum
A
- Maintenance of balance and posture
- Coordination of voluntary movements
- Motor learning
- Cognitive functions
2
Q
Principle of organisation of the cerebellum
A
- It compares movement intended to movement actually occurring
3
Q
Cerebellar peduncles
A
- Superior cerebellar peduncle
- Middle cerebellar peduncle
- Inferior cerebellar peduncle
4
Q
Functional subdivisions of the cerebellum
A
- Vestibulocerebellum
- Spinocerebellum
- Cerebrocerebellum
5
Q
What separates the cerebellum into two
A
- Vermis
6
Q
Location of the dentate nuclei
A
- Cerebellar hemispheres
7
Q
Location of interposed nucleus
A
- Paravermal or intermediate zone
8
Q
Location of fastigial nucleus
A
- Vermis
9
Q
Role of fastigial nucleus
A
- Medial descending systems –> motor execution
10
Q
Role of interposed nucleus
A
- Lateral descending systems –> motor execution
11
Q
Role of dentate nucleus
A
- Areas 4 and 6 –> motor planning
12
Q
Role of vestibular nucleus
A
- Balance and eye movements
13
Q
Lobes of the cerebellum
A
- Anterior
- Posterior
- Flocculonodular
14
Q
Effects of lesions to the cerebrocerebellum pathway
A
- Dysmetria, dysnergia, dysdiadochokinesia, intentional tremor and dysarthria
15
Q
What is dysmetria
A
- movement is not stopped in time (overshoot)
16
Q
What is dsynergia
A
- Decomposition of complex movements
17
Q
What is dysdiadochokinesia
A
- Reduced ability to perform rapidly alternating movements
18
Q
What is an intentional tremor
A
- Tremor arising when trying to perform a goal-directed movement
19
Q
What is dysarthria
A
- Articulation incoordination - incoordination in the respiratory muscles, muscles of the larynx, etc uneven speech strength and velocity
20
Q
What is limb ataxia
A
. Limb ataxia is present when a limb that has no deficits in strength wobbles during movement or misses its target
21
Q
Steps of vestibular-ocular pathway reflex
A
1) Detection of rotation of fluid movement in canal
2) Excitation of extraocular muscles on one side
3) Inhibition of extraocular muscles on the other side
4) Compensating eye movement
22
Q
Muscles used in the vestibular-ocular reflex
A
- Lateral rectus - Abducens nucleus(pons)
- Medial rectus - oculomotor nucleus(midbrain)
23
Q
Effect of lesions to the vestibulocerebellar pathway
A
- Nystagmus
24
Q
What is nystagmus
A
- Involuntary, rhythmical, repeated oscillations of one or both eyes, in any or all directions of view
- Movement of the eyes minimises the ability to focus the eyes on one point(fixation)
25
Effect of lesions in the spinocerebellar pathway
- Gait ataxia(unsteadiness of walking), and disturbance of limb tone(hypotonia) and posture
26
Cerebellar inputs
Mossy fibres and climbing fibres
27
Origin of mossy fibres
- From spinal cord and brainstem
28
Origin of climbing fibres
- From inferior olivary nucleus
29
Cerebellar outputs
- Deep cerebellar nuclei to
1) Thalami
2) Vestibular nuclei
3) Red nucleus
30
Layers of the cerebellar cortex(out to in)
- Molecular layer
- Purkinje cell layer
- Granule cell layer
- White matter
31
Where does the corticopontinecerebellar tract receive signals from
- Motor cortex
| - Red nucleus
32
How does the cerebellum receive proprioceptive feedback
Via
| - Spinocerebellum and vestibulocerebellum pathways
33
How is the actual response compared with desired response
- via the cerebrocerebellum inputs from the supplementary motor cortex and the primary motor cortex to produce error signals
34
What is the feedback loop
- Error signal is the difference between desired input and the output. The feedback comes from the output
35
Feedforward loop
- 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
36
What are error signals mainly derived from
- error signals derive mainly from sensory information e.g direction of ball whist playing tennis, error in playing a musical instrument will sound wrong
37
What are error signals sent via
- The inferior olivary nucleus which then lead onto the climbing fibres
38
What can alter the output of the purkinje cell
- 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.
39
Why is there a long-term reduction in activation of the purkinje cells to a given task
· 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.
40
Genetic causes of cerebellar dysfunction
```
· Inherited (rare)
· Frederich’s ataxia
· Spinocerebellar degeneration
· (Ataxia may occur if major connections disrupted)
· Ataxia-telengiectasia
· Von Hippel Lindau
```
Haemangioblastomas(VHL)
41
Causes of acquired symmetrical ataxia
```
· Eg-
· Alcohol
· Metabolic (B12/Thyroid/Coeliac)
· Drugs (eg phenytoin)
· Degenerative (familial, MSA)
· Immune (paraneoplastic)
```
42
Arteries supplying the cerebellum
Superior cerebellar artery (SCA)
Anterior inferior cerebellar artery (AICA)
Posterior inferior cerebellar artery (PICA)
43
Where are SCA and AICA branches of
- Basilar artery
44
What is PICA a branch of
- Vertebral artery
45
Venous drainage of the cerebellum
- Superior and inferior cerebellar veins
46
Where do the superior and inferior cerebellar veins drain into
- Superior petrosal sinus
- Transverse sinus
- Straight dural venous sinuses
47
Manifestations of cerebellar dysfunction
```
DANISH
D - Dysdiadochokinesia (difficulty in carrying our rapid, alternating movements)
A - Ataxia
N - Nystagmus(coarse)
I - Intention tremor
S - Scanning speech
H - Hypotonia
```
48
When is ataxia more profound in cerebellar dysfunction
- Often more profound if cerebellar nuclei, brainstem nuclei or white matter tracts involved(MS) than cerebellar cortex as some degree of plasticity
49
Path of climbing fibres
- neuronal projections from the inferior olivary nucleus located in the medulla oblongata
- Axons pass through the pons and enter the cerebellum via the inferior cerebellar peduncle where they form synapses with the deep cerebellar nuclei and Purkinje cells.
- Each climbing fiber will form synapses with 1–10 Purkinje cells.
