8. Motor Disorders

Question 1

what is the basal ganglia?

Answer 1

The basal ganglia consists of a number of subcortical nuclei. The grouping of these nuclei is related to function rather than anatomy – its components are not part of a single anatomical unit, and are spread deep within the brain.

Question 2

What structures form the basal ganglia?

Answer 2

Striatum (caudate nucleus and putamen), globus pallidus, subthalamic nucleus, substantia nigra

Question 3

What forms the striatum?

Answer 3

caudate nucleus and putamen - linked via grey matter bridges

Question 4

What is the Substantia nigra pars compacta

Answer 4

SNc in midbrain, source of dopamine in the midbrain

Question 5

what are the 2 parts of the Globus pallidus?

Answer 5

• Internal and external segment

Question 6

what forms the lentiform nucleus?

Answer 6

Putamen + globus pallidus (anatomically but

not functionally related)

Question 7

what is the Subthalamic nucleus?

Answer 7

(small area sitting beneath the thalamus)

in the diencephalon

Question 8

how does the basal ganglia communicate with the motor cortex ?

Answer 8

via the thalamus. Increased thalamic activity causes increased cortical activity and vice versa

Question 9

What is the major function of the basal ganglia?

Answer 9

Take the motor plan from the prefrontal cortex and determine the most appropriate set of movements that will facilitate this plan. - reinforcing appropriate movements and removing inappropriate movements
i.e. flexion or extension etc.

Question 10

What are the 2 pathways of the basal ganglia communicates with the cortex and what are they responsible for?

Answer 10

Direct pathway - facilitates appropriate movements (excitatory on cortex)
Indirect pathway - inhibits inappropriate movements (inhibitory on cortex)

Question 11

What is involved in the direct pathway? State whether excitatory or inhibitory.

Answer 11

Cortex → Putamen ┫GPi ┫Thalamus → Cortex

→ excitatory (glutamate)
┫inhibitory

Question 12

What is involved in the indirect pathway.

Answer 12

Cortex → Putamen ┫GPe ┫STN → GPi ┫Thalamus → Cortex

Question 13

What is the effect of dopamine on the direct and indirect pathway and via which receptors?

Answer 13

Dopamine released from the substantia nigra acts on the putamen:
- excites the direct pathway via excitatory D1 receptors
- Inhibits the indirect pathway by activating inhibitory D2 receptors
Hence overall excitation on the cortex

Question 14

If SNc is affected unilaterally (rare), will the signs be unilateral or contralateral?

Answer 14

Basal ganglia regulate ipsilateral motor cortex, hence if SNc is affected unilaterally (rare) there will be contralateral signs due to decussation of the corticospinal tract

Question 15

what causes Parkinson’s disease?

Answer 15

• Caused by degeneration of dopaminergic neurones in SNc
• reduced excitation of the direct pathway
• reduced inhibition of the indirect pathway
• decreased movement as reduced cortical activity

Question 16

What are the signs and symptoms of Parkinson’s?

Answer 16

• (pill rolling) tremor
• (lead pipe) rigidity
• Bradykinesia
• Hypophonia
• Micrographia
• Trouble starting and stopping
• Psychiatric features - Dementia, Depression

Question 17

why does Parkinson’s cause tremor?

Answer 17

may be related to dysfunction of indirect pathway which would normally suppress unwanted movements

Question 18

why does Parkinson’s cause bradykinesia?

Answer 18

Slow movements due to loss of cortical excitation

Question 19

why does Parkinson’s cause Hypophonia?

Answer 19

quiet speech = bradykinesia of larynx and tongue

Question 20

why does Parkinson’s cause Micrographia?

Answer 20

small handwriting = bradykinesia in hands

Question 21

What is Huntington’s Chorea and what causes it?

Answer 21

Autosomal dominant, progressive disorder
- Early stages associated with loss of inhibitory projections from striatum to GPe
• This leads to hyperkinetic features (increased movement as the brakes have been taken off the thalamus)

Question 22

describe how the basal ganglia pathway is affected in huntingtons chorea?

Answer 22

degeneration of inhibitory influences from putamen to GPe –> GPe activity increase which inhibit STN so STN activity decreases so decreased stimulation of GPi so decreased inhibition of thalamus so thalamus activity increases and thus cortical activity increases

Question 23

what is the clinical presentation of Huntington’s chorea?

Answer 23

• choreiform movements
• Dystonia
• Loss of co-ordination
• Cognitive decline and behavioural disturbances

Question 24

Define choreifrom movements and dystonia.

Answer 24

Choreiform: repetitive dance like and rapid, jerky, involuntary movement
Dystonia: uncomfortable contractions of agonists and antagonists simultaneously leading to odd postures caused by over activity in agonist/antagonist muscle circuits and loss of co-ordination between these

Question 25

What is the clinical presentation of huntington’s disease due to?

Answer 25

Lesion of the indirect pathway (between putamen and GPe)

- indirect pathway then becomes excitatory on the cortex - hyperkinesia

Question 26

What is hemiballismus and what causes it?

Answer 26

Sudden jerky movements
- caused by lesions in the subthalamic nucleus
- STN normally excites the GPi which inhibits the thalamus
- therefore reduced excitation of inhibitory neurones (increased movement)
- reduced inhibition of inappropriate movements
 Can be caused by sub-cortical stroke (lacunar infarct)
 Causes unilateral explosive (‘ballistic’) movements

Question 27

Which side do unilateral basal ganglia lesions affect and why?

Answer 27

The contralateral side

• basal ganglia communicates with the ipsilateral cortex
• ipsilateral cortex gives off contralateral motor neurones

Question 28

What are the 2 parts of the cerebellum and which parts of the body are they related to?

Answer 28

 Midline vermis and two laterally placed hemispheres

 Vermis deals with trunk, hemispheres with the ipsilateral side of the body

Question 29

What structure connects the cerebellum to the brainstem?

Answer 29

Cerebellar peduncles

• superior peduncle to the midbrain
• middle peduncle to the pons
• inferior peduncle to the medulla

Question 30

what does the cerebellum sit above and what is the relevance of this?

Answer 30

Sits above the fourth ventricle
• Cerebellar lesions (e.g. tumours) can cause
hydrocephalus

Question 31

what is the role of the cerebellum?

Answer 31

 Obscure!
 However, has a clear role in the sequencing and co-ordination ofmovements
 Uses sensory information to decide upon the most appropriate sequence of movements to perform an action

Question 32

describe how the basal ganglia and cerebellum work to complete a task

Answer 32

• basal ganglia determine the most appropriate set of movements that will facilitate the plan
• The cerebellum looks at the position of the limbs currently and determines an appropriate sequence to conduct the motor plan in

Motor plan – ‘pick up a cup of tea’
Basal ganglia say ‘you need to flex your fingers and inhibit finger extension, flex your wrist and inhibit wrist extension and flex your elbow and inhibit elbow extension
Cerebellum says ‘you need to move the fingers first, then the wrist and finally the elbow’

Question 33

what are the inputs to the cerebellum?

Answer 33

 cerebellum has profuse sensory inputs from proprioceptive neurones and the sensory cortices
 Cerebellum receives sensory input from ipsilateral spinal cord and contralateral sensory cortices.

Question 34

what side will be affected in cerebellar lesions?

Answer 34

Its outputs are to the contralateral motor cortex. Hence, ipsilateral signs of cerebellar damage due to decussation of corticospinal pathway

Question 35

WHat are the symptoms of cerebellar lesion?

Answer 35

DANISH:

• dysdiadochokinesia
• ataxia
• nystagmus
• intention tremor
• slurred speech (dysarthria)
• hypotonia

Question 36

Define dysdiadochokinesia.

Answer 36

Impaired ability to perform rapid alternating movements

Question 37

Define ataxia.

Answer 37

Unsteady gait as a result of difficulty sequencing lower limb muscle contractions as well as loss of unconscious proprioception from lower limbs

Question 38

How is intention tremor tested for?

Answer 38

Finger to nose test

Question 39

What is the Romberg test?

Answer 39

Test for sensory ataxia

• patient stood up straight with eyes closed (remove vision, used for balance)
• if they fall then positive sign
• falling suggests loss of proprioception (dorsal column)

Question 40

define nystagmus?

Answer 40

Flickering eye movements due to malcoordination of extraocular muscles

Question 41

define intention tremor?

Answer 41

A tremor that worsens as a target is approached