Session 6: Motor Disorders

Question 1

Answer 1

Question 2

Answer 2

Question 3

What is the basal ganglia made of?

Answer 3

Substantia nigra pars compacta

Striatum

Lentiform nucleus

Subthalamic nucleus

Question 4

What makes up the striatum?

Answer 4

The caudate and putamen

Question 5

What makes up the lentiform nucleus?

Answer 5

The putamen and the globus pallidus

Question 6

What are the parts of the globus pallidus?

Answer 6

Globus pallidus interna

Globus pallidus externa

Question 7

Function of the basal ganglia.

Answer 7

Communicates with the motor cortex in order to reinforce appropriate movements and also inhibit inappropriate movements.

An example is raising a glass:

Need to reinforce appropriate movements which would be elbow flexion and shoulder flexion.

Need to inhibit inappropriate movements which would be elbow extension and shoulder extension.

Question 8

Basal ganglia communicates with the motor cortex via two pathways.

Which?

Answer 8

Direct pathway

Indirect pathway

Question 9

Function of direct pathway.

Answer 9

Reinforces appropriate movement.

Question 10

Function of indirect pathway.

Answer 10

Inhibit inappropriate movement

Question 11

Explain the functions of the cerebellum.

Answer 11

Communicates with the motor cortex as well as with proprioception.

Proprioception receptors send an afferent ascending signal via the spinocerebellar tract to the cerebellum. This is in order for the cerebellum to know the position of the limbs in space.

This is important in order for what the cerebellum is about to do next:

Select the appropriate sequence of movements.

Question 12

Where is dopamine produced?

Answer 12

Substantia nigra pars compacta

Question 13

Explain the action of dopamine in the basal ganglia.

Answer 13

Dopamine acts on D1 receptors on striatal neurones in order to excite the direct pathway.

Dopamine also acts on D2 receptors which inhibits the indirect pathway (leading to a net excitatory signal)

Question 14

What will a basal ganglia lesion affect?

Answer 14

It will affect the contralateral side of the body.

Question 15

Why does a basal ganglia lesion lead to a contralateral presentation?

Answer 15

Because the basal ganglia circuit where it communicates with the motor cortex communicates with the ipsilateral side.

This means that there is no decussation in the communication between basal ganglia and motor cortex.

When a motor signal is then sent down via the corticospinal tract it will cause a contralateral presentation.

Question 16

Are most basal ganglia lesions usually contralateral?

If not, what are they?

Answer 16

No, they are usually bilateral due to neurodegeneration.

Question 17

What will a cerebellar lesion affect?

Answer 17

The ipsilateral side of the lesion.

Question 18

Explain why a cerebellar lesion present with ipsilateral symptoms.

Answer 18

Because the cerebellum communicates with the contralateral cerebral hemisphere. This is via the corticopontine pathway where the afferent fibre synapse in the pontine nucleus and then in the pons the fibres will decussate and communicate with the contralateral cerebellum.

There is then a signal going back to the motor cortex via the cerebello-thalamo-cortical pathway where there is decussation again.

Lastly the response is via the corticospinal pathway which also decussate to the same side as the lesion.

Question 19

What is Parkinson’s disease?

Answer 19

Caused by degeneration of dopaminergic neurones in SNc leading to lower levels of dopamine.

Question 20

What is the consequence of the lower levels of dopamine?

Answer 20

There is less excitation of the direct pathway and also less inhibition of the indirect patway.

This leads to less motor activity.

Question 21

Symptoms and signs of Parkinson’s disease.

Answer 21

Pill rolling tremors

Lead pipe rigidity aka cog-wheel rigidity

Bradykinesia where there are problems with initiating and terminating movement.

Hypophonia

Decreased facial movement / mask-life facies

Micrographia

Dementia

Depression

Question 22

Why does bradykinesia happen in Parkinson’s?

Answer 22

Due to loss of cortical excitation

Question 23

Treatment of Parkinson’s.

Answer 23

Levodopa which is converted into dopamine in the brain.

Deep brain stimulation (e.g. of subthalamic nucleus)

Question 24

What is Huntington’s chorea?

Answer 24

An autosomal dominant and progressive disorder that usually presents in 30-50 years of age.

This is due to the loss of the inhibitory projections from striatum to GPe.

Question 25

What are the consequences of the loss of inhibitory projections from stiatum to GPe?

Answer 25

Hyperkinetic features since the 'brakes' have been taken off the thalamus.

Question 26

Signs and symptoms of Huntington's chorea.

Answer 26

**Bilateral** chorea (dance-like movements) Dystonia Loss of co-ordination Cognitive decline and behavioural disturbances

Question 27

Why does chorea occur in Huntington's?

Answer 27

Increased motor cortex activation

Question 28

Why does dystonia occur in Huntington's?

Answer 28

Uncomfortable contractions of agonists **and** antagonists **simultaneously** leading to odd postures and pain.

Question 29

What is hemiballismus?

Answer 29

Usually caused by damage to subthalamic nucleus.

Question 30

What is the consequence of damage to the subthalamic nucleus?

Answer 30

It normally inhibits the thalamus by stimulation of GPi. If there is damage there will be increased excitation of the motor cortex.

Question 31

What can hemiballismus be caused by?

Answer 31

Sub-cortical stroke also called a lacunar infarct.

Question 32

Symptoms and signs of hemiballismus.

Answer 32

Similar to Huntington's where there is involuntary commonly called **ballistic** movements. The difference here is that the ballistic movements are **unilateral**.

Question 33

Anatomy of the cerebellum.

Answer 33

Midline vermis and two laterally placed hemispheres

Question 34

Functions of the vermis.

Answer 34

Deals with cerebellar movements of the trunk.

Question 35

Functions of the cerebellar hemispheres.

Answer 35

Deals with cerebellar movements of the ipsilateral sides of the body.

Question 36

How does the cerebellum communicate with the cerebrum?

Answer 36

Via the cerebellar peduncles. There are three peduncles: Superior, middle and inferior which communicate with the midbrain, pons and medulla respectively.

Question 37

What does the cerebellum sit on top of?

Answer 37

The 4th ventricle

Question 38

What is the relevance of the cerebellum sitting on top of the 4th ventricle?

Answer 38

A lesion of the cerebellum can cause hydrocephalus due to compression of the 4th ventricle.

Question 39

Signs of cerebellar disease/lesion.

Answer 39

DANISH Dysdiadochokinesia Ataxia Nystagmus Intention tremor Slurred speech Hypotonia

Question 40

What is dysdiadochokinesia?

Answer 40

Difficulty with rapidly alternating movements

Question 41

Explain the cerebellar ataxia.

Answer 41

Unstead gait as a result of difficulty sequencing lower limb muscle contractions.

Question 42

How do you distinguish between sensory and cerebellar ataxia?

Answer 42

By doing Rhomberg's test.

Question 43

Explain Rhomberg's test.

Answer 43

Tell the patient to close their eyes. If the patient falls over that is a positive Romberg's test and a sign of **sensory ataxia.** If the test is negative then it can be **cerebellar ataxia.**

Question 44

What is nystagmus?

Answer 44

Rapidly moving eyes with vertigo This is due to malcoordination of the extraocular muscles.

Question 45

What are intention tremors?

Answer 45

Low frequency tremors

Question 46

Why does slurred speech occur in cerebellar lesions?

Answer 46

Malcoordination of laryngeal and tongue musculature.