Motor: basal ganglia

Question 1

What is the difference between the basal ganglia and the cerebellum?

Answer 1

The basal ganglia inhibits the motor cortex’s connections to voluntary muscles via the thalamus.
The cerebellum, stimulates the action of the motor cortex.

Question 2

What structures does the basal ganglia consist of?

Answer 2

Caudate nucleus
Putamen
Substantia nigra pars compacta and pars reticulata
Subthalamic nucleus
Globus pallidus interna and externa

Question 3

What are the functions of the basal ganglia?

Answer 3

Planning and programming movement
Elaborating associated movement
Coordinating and modifying movements
Performing movements in order

Question 4

Describe the connections to and from the basal ganglia i.e. direct and indirect pathway

Answer 4

Info from primary motor/premotor/supplementary motor cortex is sent to neurones in the striatum (caudate and putamen).
Direct pathway: putamen -> globus pallidus interna + substantia nigra.
Indirect pathway: putamen -> globus pallidus externa -> subthalamic nucleus -> globus pallidus interna
Both then project to the thalamus and back to SMA and PMA for programming of movement

Intrinsic connections from SNc to caudate and putamen nuclei

Question 5

What is the difference in effect of the direct and indirect pathway of the basal ganglia?

Answer 5

Direct pathway EXCITES motor cortex. The substantial nigra feeds back to the striatum and excites dopaminergic neurones. The thalamus excites the cortex.
Indirect pathway INHIBITS motor cortex

Question 6

Which are the inhibitory and excitatory neurotransmitters of the basal ganglia?

Answer 6

Inhibitory: GABAnergic
Excitatory: Dopaminergic, glutamate

Question 7

Which other cortices apart from motor is the basal ganglia involved with i.e. a sub-cortical loop?

Answer 7

Prefrontal association cortex

Limbic cortex

Question 8

What is the histological presentation of PD?

Answer 8

Loss of dopaminergic nigrostriatal pathway -> Inclusion (Lewy) bodies and aggregates of proteins in neurones

Question 9

Describe the nigrostriatal pathway in PD?

Answer 9

Degeneration of dopaminergic neurones in SNc.
Increased activity of GPi neurones from increased activity of STN.
Less feedback to striatum causes disruption of excitation and inhibition.
More inhibitory signals to VA and VL thalamic nuclei form GPi/SNr causing reduced output from the motor cortex.

Question 10

List the signs of PD

Answer 10

Bradykinesia
Hypomimic face
Akinesia
Stooped posture
'Pill rolling tremor': at rest
Parkinsonian gait
Rigidity

Question 11

What is the cause of Huntington’s disease?

Answer 11

Autosomal dominant genetic condition

Mutation on chromosome 4 of huntingtin gene

Question 12

What is the pathology of Huntington’s?

Answer 12

Loss of GABAnergic neurones in the striatum
Decreased inhibition of STN
Less inhibition of GPi/SNr complex (inhibitory to motor cortex)
Excessive excitatory input
Hyperkinetic disease

Question 13

What is choreic movement?

Answer 13

Rapid jerky involuntary movements starting in the hands and face;
Speech impairment
Difficulty swallowing
Impaired gait
Dementia and cognitive decline

Question 14

What are the different divisions of the cerebellum horizontally and sagittally?

Answer 14

Horizontal divisions; anterior, posterior, flocculonodular

Sagittal; vermis, intermediate hemisphere, lateral hemisphere

Question 15

Which side of the body does the cerebellum control?

Answer 15

Connects to the ipsilateral side of the body and therefore contralateral cerebral hemisphere

Question 16

What is the floccunodoluar lobe often referred to as and what does it do and its stimuli?

Answer 16

Vestibulocerebellum
Regulation of gait, posture (spatial orientation) and balance
Coordination of head movements to eye movements.

Receives input from vestibular nuclei and semicircular canals.
Visual input from superior colliculi and visual cortex.

Question 17

What is the spinocerebellum?

Answer 17

Consists of the vermis and intermediate hemisphere
Axial portions of the body, trigeminal , auditory and visual input project to the vemis.
Distal body and limb movements project to the intermediate hemisphere (dorsal column proprioception and spinocerebllar tract).

Coordination of speech
Adjusts muscle tone
Limb movements

Question 18

What is the cerebrocerebellum?

Answer 18

Consists of the lateral hemisphere
Involved in skilled movements, attention, processing of language
Emotional control

Question 19

What are the three layers of the cerebellar cortex?

Answer 19

Molecular layer (outer layer containing axons of granule cells and dendrites of purkinje cells)
Purkinje cells
Granule cells

Question 20

What are the fibre types found in the cerebellar cortex?

Answer 20

Mossy fibres; enter at granular cell layer, synapse with purkinje cells
Climbing fibres; enter at purkinje cell layer (from inferior olivary nucleus). Compare inputs and project to the deep cerebellar nuclei -> thalamus, postural and vestibular cortex

Question 21

What are the three deep nuclei in the cerebellar cortex and where do they project to?

Answer 21

Fastigial nucleus; vestibular and reticular nuclei for balance
Interposed and dentate nucleus; thalamus and red nucleus to control voluntary movements

Question 22

What are the three sources of input into the cerebellum?

Answer 22

Mossy fibres from spinocerebellar pathways
Mossy fibres from pons bringing info from cerebral cortex
Climbing fibres from inferior olive

Question 23

What is ataxia?

Answer 23

Poor coordination, brain is unable to coordinate posture, strength and direction of limb movements

Question 24

What is Romberg’s sign?

Answer 24

Romberg positive: imbalance when eyes are closed

[Cerebellar lesions will result in negative romberg sign]

Question 25

Describe the presentation of vestibulocerebellar or flocculonodular syndrome

Answer 25

Ataxic gait
Absence of Romberg’s sign
Nystagmus (uncontrolled eye movements)

Question 26

Spinocerebellar syndrome: presentation and cause

Answer 26

Degeneration and atrophy associated with chronic alcoholism
Abnormal gait
Wide-based stance
Hypotonia

Question 27

Cerebrocerebellar or lateral hemisphere syndrome: presentation and cause

Answer 27

Tremor and clumsy movements e.g. dysmetria
Coordination problems (dysdiadokinesia)

Question 28

What is dysdiadokinesia?

Answer 28

Inability to perform rapid alternating movements e.g. rapidly pronating and supinating hands and forearm

Question 29

What is scanning speech?

Answer 29

Staccato speech

Question 30

What is an intention tremor and how is this assessed?

Answer 30

Increasing oscillating limb closer to the target

Use nose-finger tracking to assess