S6: motor disorders

Question 1

List the structures which form the basal ganglia

Answer 1

Substantia nigra – source of dopamine in the midbrain
Striatum (caudate nucleus & putamen)
Globus pallidus (internal & external segment)
Lentiform nucleus = putamen + globus pallidus
Subthalamic nucleus

Question 2

What is the function of the basal ganglia?

Answer 2

Reinforcing appropriate movements and removing inappropriate movements
Direct pathway reinforces appropriate movements
Indirect pathway edits out inappropriate movements

Question 3

Describe the action of dopamine on the motor cortex

Answer 3

Facilitates movement by exciting the motor cortex
Excites the direct pathway by stimulating excitatory D1 receptors on striatal neurones
Inhibits the indirect pathway by activating inhibitory D2 receptors on striatal neurones

Question 4

Describe lesions to the basal ganglia

Answer 4

Bilateral – neurogenerative disease (means a symmetrical lesion)
Basal ganglia regulate ipsilateral cortex, hence if SNc is affected unilaterally (rare) there will be contralateral signs due to decussation of the CST

Question 5

Describe Parkinson’s disease

Answer 5

Caused by degeneration of dopaminergic neurones in SNc

Therefore, lost the dopamine-driven facilitation of movement via both pathways

Question 6

Outline the symptoms and signs of Parkinson’s disease

Answer 6

Tremor
Rigidity 
Bradykinesia – slow movements due to loss of cortical excitation 
Hypophonia (quiet speech)
Psychiatric features

Question 7

Describe Huntington’s chorea

Answer 7

Autosomal dominant, progressive disorder
Early onset, 30-50 years old
Early stages associated with loss of inhibitory projections from striatum to GPs

Question 8

Outline the symptoms and signs of Huntington’s chorea

Answer 8

Chorea (dance-like movements due to increased motor cortex activation)
Dystonia (uncomfortable contractions of agonists and antagonists)
Loss of coordination
Cognitive decline and behavioural disturbances

Question 9

Describe hemiballismus

Answer 9

Rare disorder
Caused by damage to subthalamic nucleus which normally inhibits the thalamus via GPi
Can be caused by sub-cortical stroke (lacunar infarct)
Causes unilateral explosive movements

Question 10

Describe the anatomy of the cerebellum

Answer 10

Midline vermis and two laterally placed hemispheres
-vermis deals with trunk, hemispheres with the ipsilateral side of the body
Communicates with the rest of the CNS via the cerebellar peduncles (superior -> midbrain, middle -> pons & inferior -> medulla)
Sits above the fourth ventricle -> cerebellar lesions can cause hydrocephalus

Question 11

What is the normal function of the cerebellum?

Answer 11

Uses sensory function to decide upon the most appropriate sequence of movements to perform an action
Hence, cerebellum has profuse sensory inputs from proprioceptive neurones and the sensory cortices

Question 12

Describe lesions to the cerebellum

Answer 12

Cerebellum receives sensory input from ipsilateral spinal cord and contralateral sensory cortices
Its outputs are to the contralateral motor cortex
Therefore, it will cause ipsilateral signs and symptoms

Question 13

Outline the signs of cerebellar disease

Answer 13

Dysdiadochokinesia – difficulty with rapidly alternating movements
Ataxia – unsteady gait
Nystagmus – flickering eye movements
Intention tremor – worsens as a target is approached
Slurred speech – miscoordination of laryngeal and tongue musculature
Hypotonia