Motor Pathways: Basal Ganglia and Cerebellum

Question 1

What is the collective term given to the basal ganglia and cerebellum?

Answer 1

Extrapyramidal system

Question 2

What is the function of the basal ganglia>

Answer 2

Elaborating associated movements (e.g. swinging arms when walking)
Moderating + coordinating movement (suppressing unwanted movement)
Performing movements in order

Question 3

Where is the basal ganglion located?

Answer 3

White matter in the middle of the brain

Question 4

What is the basal ganglia composed of?

Answer 4

Caudate nucleus
Lentiform nucleus (globus pallidus + putamen)
Subthalamic nucleus
Substantia nigra

Question 5

Where do the projections go after leaving the basal ganglion structures?

Answer 5

To the thalamus
Then to the cortex (supplementary motor area + primary motor area = 2 regions involved in movement preparation + planning)

Question 6

What causes Parkinson’s disease?

Answer 6

Neuronal degeneration of dopaminergic neurones that originate in the substantia nigra + project to the striatum

Question 7

State the 5 main motor signs of Parkinson’s disease.

Answer 7

Bradykinesia: slow movement  
Akinesia: difficulty initiating movements  
Hypomimic face: expressionless face  
Tremor at rest
Rigidity: increase in muscle tone

Question 8

Describe the Parkinsonian gait.

Answer 8

Walking slowly, small steps, shuffling feet, reduced arm swing
Stooped posture with head + body bent forwards + downwards

Question 9

What is Huntington’s disease caused by?

Answer 9

Abnormality on chromosome 4 (autosomal dominant)
CAG repeat
Caused by the degeneration of GABAergic neurones in the striatum (1st the caudate, then the putamen)

Question 10

What are the consequences of the pathology of Huntington’s with regards to the circuitry of the basal ganglia?

Answer 10

Inhibitory effect of the indirect pathway no longer keeps the direct pathway under control so the cortex will be hyperexcitable.
Patients will continuously have abnormal movements because the cortex is continuously sending involuntary commands for movements.

Question 11

What are the 6 main signs of Huntington’s disease and how does the disease progress?

Answer 11

Choreic movements: rapid, jerky, involuntary movements of the body (hands + face affected 1st, increases over time until patients are totally incapacitated)
Speech impairment
Difficulty swallowing
Unsteady gait (due to involuntary activity)
Cognitive decline
Dementia.

Question 12

State the 3 layers of the cerebellar cortex.

Answer 12

Granular cell layer (many small neurones involved in processing)
Purkinje cells (large projecting cells with huge dendritic trees)  
Molecular layer (outer, not many neurones)

Question 13

Describe the input to the cerebellum

Answer 13

Inferior olive projects to Purkinje cells via Climbing fibres
All other input to granular cells via mossy fibres + then onwards via parallel fibres

Question 14

Functionally, the cerebellum can be divided in three. What are these three divisions?

Answer 14

Vestibulocerbellum
Spinocerebellum
Cerebrocerebellum

Question 15

What is the role of the vestibulocerebellum?

Answer 15

Regulation of gait, posture + equilibrium

Coordination of head movements with eye movements

Question 16

What are the roles of the spinocerebellum?

Answer 16

Coordination of speech
Adjustment of muscle tone
Coordination of limb movement

Question 17

Which part of the cerebellum is part of the cerebrocerebellum?

Answer 17

Lateral hemisphere

Question 18

What are the 5 main functions of the cerebrocerebellum?

Answer 18

Coordination of skilled movements  
Cognitive function  
Attention 
Processing of language  
Emotional control

Question 19

State 3 syndromes caused by dysfunction of different parts of the cerebellum.

Answer 19

Vestibulocerebellar syndrome
Spinocerebellar syndrome
Cerberocerebellar syndrome

Question 20

What are the symptoms of vestibulocerebellar syndrome?

Answer 20

Similar to vestibular disease
Gait ataxia
Tendency to fall (even when sitting with eyes open)

Question 21

What behavioural habit is spinocerebellar syndrome associated with?

Answer 21

Chronic alcoholism

Question 22

Describe the symptoms of spinocerebellar syndrome.

Answer 22

Mainly affects legs

It causes abnormal gait + a wide-based stance

Question 23

Describe the symptoms of cerebrocerebellar syndrome.

Answer 23

Mainly affects arms + coordinated movements (tremor)

Speech becomes very hesitant + slow (staccato)

Question 24

What are the 5 main signs of cerebellar disorders?

Answer 24

Ataxia: general impairments in movement coordination + accuracy
Dysmetria: inappropriate force + distance for target-directed movements
Intention tremor: increasingly oscillatory trajectory of a limb in a target directed movement (nose-finger tracking)
Dysdiadochokinesia: inability to perform rapid alternating movements
Scanning speech: staccato, due to impaired coordination of speech muscles

Question 25

State a hereditary and acquired cause of cerebellar dysfunction

Answer 25

Hereditary – Friedreich’s Ataxia

Acquired – Multiple Sclerosis

Question 26

What is the striatum composed of?

Answer 26

Caudate
Putamen
External global palidus

Question 27

Which 3 areas in basal ganglia nuclei are commonly affected by disease?

Answer 27

Nigro-striatal system= PD
Striatum->Globus pallidus (int.)= HD
Subthalamic nucleus->Globus pallidus (int.)= Ballism

Question 28

Describe the cerebellar output

Answer 28

All output from Purkinje cells via deep nuclei