Motor Pathways: Basal Ganglia and Cerebellum Flashcards

1
Q

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

A

Extrapyramidal system

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2
Q

Broadly speaking, what is the role of this system?

A

It checks that the movement selected by the motor cortex is correct
Both parts of the extrapyramidal system has functions aside from modulating motor control

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3
Q

Where is the basal ganglion located?

A

White matter in the middle of the brain

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4
Q

What are the different parts of the basal ganglia?

A

Striatum = caudate + putamen
Globus Pallidus = external segment (GPext) + internal segment (GPint)
Substantia Nigra = pars compacta (SNc) + pars reticulata (SNr)
Subthalamic Nucleus

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5
Q

What is the function of the basal ganglia?

A

It is involved in planning and coordinating movement
It elaborates associated movements (e.g. swinging arms when walking)
Contribute to the smoothness of complex action
Involved in moderating and coordinating movements

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6
Q

Describe the structure of the direct pathway in the basal ganglia.

A

Fibres initially come from the motor cortex to the striatum (caudate and putamen)
Direct Pathway: putamen –> globus pallidus internal segment + substantia nigra pars reticulata

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7
Q

Describe the structure of the indirect pathway in the basal ganglia.

A

Fibres initially come from the motor cortex to the striatum (caudate and putamen)
Indirect Pathway: putamen –> globus pallidus external segment –> subthalamic nucleus –> globus pallidus internal segment

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8
Q

What is the difference in the function of the direct and indirect pathways?

A

Direct Pathway = excitatory on the motor cortex

Indirect Pathway = inhibitory on the motor cortex

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9
Q

What extra component modulates the function of the direct and indirect pathways?

A

Nigro-striatal pathway

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10
Q

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

A

They go to the thalamus
From the thalamus they go to the cortex (supplementary motor area and primary motor area = two regions involved in movement preparation and planning)

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11
Q

Describe how the basal ganglia are involved in choosing correctmotor programmes to carry out particular functions.

A

The basal ganglia and cortex form a processing loop.
The basal ganglia enable proper motor programmes (stored in the cortex) via the direct pathway (exicitatory)
The basal ganglia inhibit the competing motor programmes via the indirect pathway
In summary, the basal ganglia and its direct and indirect pathways make sure that appropriate motor commands get transmitted down the hierarchy.

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12
Q

Connections with which parts of the brain allow the basal ganglia to have a role in enabling various cognitive, executive and emotional programmes?

A

Prefrontal association cortex

Limbic cortex

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13
Q

What causes Parkinson’s disease?

A

Parkinson’s disease is the neuronal degeneration of dopaminergic neurones in the substantia nigra pars compacta
It is caused by the progressive depletion of dopaminergic neurones
NOTE: symptoms only appear hen 80% of the dopamine cells in the substantia nigra have died

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14
Q

What are the consequences of this with regards to the circuitry of the basal ganglia?

A

The loss of nigro-striatal dopaminergic axons in the caudate and putamen mean that the connection between the striatum (caudate and putamen) and the substantia nigra pars compacta is lost.
This means that the direct pathway is reduced and so the excitation of the motor cortex is reduced.
The lack of excitatory input interferes with the ability of the motor cortex to generate commands for voluntary movement, resulting in poverty of movement.

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15
Q

State the main signs of Parkinson’s disease.

A
Bradykinesia – slow movement  
Akinesia – difficulty in the initiation of movements  
Hypomimic face – expressionless face  
Tremor  
Rigidity – increase in muscle tone
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16
Q

Describe the Parkinsonian gait.

A

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

17
Q

What is Huntington’s disease caused by?

A

Abnormality on chromosome 4 (autosomal dominant)

Caused by the degeneration of GABAergic neurones in the striatum (firstly the caudate and then the putamen)

18
Q

What are the consequences of this with regards to the circuitry of the basal ganglia?

A

The 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.

19
Q

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

A

Choreic movements – rapid, jerky, involuntary movements of the body
The hands and face are affected first
Chorea gradually increases over time until the patients are totally incapacitated by it
Later on the patients will develop cognitive decline and dementia.

20
Q

State the 3 lobes of the cerebellum.

A

Anterior
Posterior
Flocculonodular

21
Q

The cerebellum is divided sagitally into 3 zones. What are these zones?

A

Vermis (midline)
Intermediate hemisphere (closest to vermis)
Lateral hemisphere

22
Q

State the 3 layers of the cerebellar cortex.

A

Granule cell layer
Purkinje cells
Molecular layer

23
Q

Name the 3 deep nuclei that are involved in the connections of thecerebellum with other parts of the body. Include their function.

A

Fastigial = involved in control of balance and connected with vestibular nuclei
Interposed + Dentate = both involved in voluntary movement and are connected to the thalamus and the red nucleus

24
Q

What are the 3 sources of input into the cerebellum and what do they connect with?

A

Mossy Fibres – from the cortex and pons (corticopontine fibres)
Mossy Fibres – from the spinocerebellar tract
Climbing Fibres – from the inferior olive

25
Q

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

A

Vestibulocerbellum
Spinocerebellum
Cerebrocerebellum

26
Q

What is the role of the vestibulocerebellum?

A

Vestibulocerbellum is the flocculonodular lobe
It is connected to vestibular nuclei
Involved in balance, posture and regulation of gait
It is also involved in coordination of head movements with eye movements

27
Q

Which parts of the cerebellum are part of the spinocerebellum?

A

Vermis and intermediate hemisphere

28
Q

From where does the spinocerebellum receive inputs?

A

Afferents from axial portions of the body, visual, auditory and trigeminal inputs –> vermis
Afferents from limbs –> intermediate hemisphere

29
Q

What are the roles of the spinocerebellum?

A

Coordination of speech
Adjustment of muscle tone
Coordination of limb movement

30
Q

Which part of the cerebellum is part of the cerebrocerebellum?

A

Lateral hemisphere

31
Q

From where does the cerebrocerebellum receive inputs and what are its main functions?

A
It receives projections from the cortex  
Main functions are: 
 Coordination of skilled movements  
 Cognitive function  
 Attention 
 Processing of language  
 Emotional control
32
Q

In summary, what are the four main functions of the cerebellum?

A

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

33
Q

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

A

Vestibulocerebellar syndrome/Flocculonodular lobe syndrome
Spinocerebellar syndrome
Cerberocerebellar syndrome

34
Q

What are the symptoms of vestibulocerebellar syndrome?

A

This syndrome is similar to vestibular disease

Patients tend to lose their balance with gait ataxia and a tendency to fall.

35
Q

What behavioural habit is spinocerebellar syndrome associated with?

A

Chronic alcoholism

36
Q

Describe the symptoms of spinocerebellar syndrome.

A

Mainly affects the legs It causes abnormal gait and a wide-based stance

37
Q

Describe the symptoms of cerebrocerebellar syndrome.

A

Damage mainly affects the arms
It affects coordinated movements
Speech becomes very hesitant and slow (staccato)

38
Q

What are the main signs of cerebellar disorders?

A

Ataxia– general impairments in movement coordination and accuracy
Dysmetria– inappropriate force and 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

39
Q

State a hereditary and acquired cause of the symptoms listed above.

A

Hereditary – Friedreich’s Ataxia

Acquired – Multiple Sclerosis