Motor Disorders

Question 1

What are basal ganglia

Answer 1

-

Question 2

What is the SNc

Answer 2

Substantia nigra pars compacta (SNc, source of dopamine in the midbrain)

Question 3

What is the striatum

Answer 3

 Striatum (receives input from SNc and cortex)
• Caudate nucleus (c-shaped nucleus lining lateral
ventricle) • Putamen
Caudate + putamen = striatum (functionally related)

Question 4

Desribe the globus pallidus

Answer 4

Globus pallidus

• Internal and external segment ss

Question 5

What is the lentiform ucleus

Answer 5

Putamen + globus pallidus = lentiform nucleus (anatomically but
not functionally related)

Question 6

What is the subthalamic ucleus

Answer 6

Subthalamic nucleus (small area sitting beneath the thalamus)

Question 7

How do basal ganglia communicate with motor cortex

Answer 7

The basal ganglia communicate with the motor cortex via the

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

Question 8

Describe the normal function of the basal ganglia

Answer 8

Normal function
 Unclear! And not a priority in your learning
 Probable role in reinforcing appropriate movements and
removing inappropriate movements. Think about a simple behaviour like picking up a cup of tea – you need to facilitate appropriate movements (e.g. elbow flexion) and suppress inappropriate movements (e.g. elbow extension)

Question 9

What do the direct and indirect pathways do

Answer 9

Direct pathways reinforces appropriate movements (excitatory to motor cortex)
 Indirect pathway edits out inappropriate movements (inhibitory to motor cortex)

Question 10

How does dopamine facilitate movement

Answer 10

Dopamine facilitates movement by exciting the motor cortex (excites direct pathway by stimulating excitatory D1 receptors on striatal neurones taking part in the direct pathway, inhibits indirect pathway by activating inhibitory D2 receptors on striatal neurones taking part in the indirect pathway) ss

Question 11

Are basa ganglia signs ipsilateral or contralateral

Answer 11

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 12

What is Parkinson’s disease caused by

Answer 12

Parkinson’s disease

 Caused by degeneration of dopaminergic neurones in SNc
 Therefore have lost the dopamine-driven facilitation of
movement via both pathways

Question 13

What are teh symptoms and signs of Parkinson’s

Answer 13

Symptoms and signs:
• Tremor (unclear mechanism, but may be related to dysfunction of indirect pathway which would normally suppress unwanted movements)
• Rigidity (unknown mechanism, may be related to lack of co-ordination between agonists and antagonists)
• Bradykinesia (best understood mechanism. Slow movements due to loss of cortical excitation)
• Hypophonia (quiet speech = bradykinesia of larynx and tongue)
• Decreased facial movement / mask-like facies (bradykinesia of face)
• Micrographia (small handwriting = bradykinesia in hands)
• Dementia (possible progression of currently unknown
causative agent (e.g. protein aggregates))
• Depression (basal ganglia also have a role in cognition
and mood)

Question 14

What is Huntington’s disease

Answer 14

Huntington’s chorea
 Autosomal dominant, progressive disorder
 Early onset around 30-50 years old
 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 15

What are the features of Huntington’s disease

Answer 15

Features
• Chorea (dance-like movements due to increased motor cortex activation)
• 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)
• Loss of co-ordination (similar to above presumably)
• Cognitive decline and behavioural disturbances (related
to role of basal ganglia in higher metal functions)

Question 16

Wat is hemiballismus

Answer 16

Hemiballismus
 Rare disorder
 Can be 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 (‘ballistic’) movements

Question 17

Describe the anatomy of the cerebellum

Answer 17

Cerebellum
o Anatomy
 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 (different to the cerebral peduncles!)
• Superior cerebellar peduncle connects to midbrain
• Middle cerebellar peduncle connects to pons
• Inferior cerebellar peduncle connects to medulla
 Sits above the fourth venricle
• Cerebellar lesions (e.g. tumours) can cause
hydrocephalus

Question 18

What are the oral functions of the cerebellum

Answer 18

Normal functions
 Obscure! And not a priority in your learning
 However, has a clear role in the sequencing and co-ordination of
movements
 Uses sensory information to decide upon the most appropriate
sequence of movements to perform an action
 Works with basal ganglia which decide most appropriate
movements. Cerebellum then sequences these movements. So, to develop the picking up a cup of tea example: basal ganglia say that elbow flexion, shoulder flexion, finger flexion and wrist flexion are most appropriate. Cerebellum then puts these in most appropriate sequence based upon current position of limb (maybe finger flexion followed by wrist extension followed by elbow then shoulder depending upon position).
 Hence, cerebellum has profuse sensory inputs from proprioceptive neurones and the sensory cortices
 Cerebellum receives sensory input from ipsilateral spinal cord and contralateral sensory cortices. Its outputs are to the contralateral motor cortex. Hence, ipsilateral signs of cerebellar damage due to decussation of corticospinal pathway

Question 19

What are signs of cerebellar disease

Answer 19

Signs of cerebellar disease  Dysdiadochokinesia
• Difficulty with rapidly alternating movements (presumably as a result of a problem with sequencing pronation-
supination-pronation-supination…)  Ataxia
• Unsteady gait as a result of difficulty sequencing lower limb muscle contractions as well as loss of unconscious proprioception from lower limbs
 Nystagmus
• Flickering eye movements due to malcoordination of extraocular muscles
 Intention tremor
• A tremor that worsens as a target is approached
 Slurred speech (dysarthria)
• Caused by malcoordination of laryngeal and tongue
musculature  Hypotonia
• Unclear mechanism