S6) Motor Disorders

Question 1

What are the components of the motor pathway?

Answer 1

• Corticospinal tract
• Corticobulbar tract
• Extrapyramidal tracts

Question 2

Describe the anatomical location of the cerebellum

Answer 2

• Located in the posterior cranial fossa
• Separated from the occipital and parietal lobes by the tentorium cerebelli
• Separated from the pons by the 4th ventricle

Question 3

What is the role of the cerebellum?

Answer 3

It has an important role in motor control and coordination

→ work with basal ganglia to detriment correct actions and sequence

→ profuse sensory inputs from proprioceptive neurones and sensory cortices

Question 4

Describe the components of the cerebellum

Answer 4

• Consists of:

I. Vermis which regulates trunk musculature

II. Two lateral cerebellar hemispheres which regulate distal structures i.e. limbs

• Tracts are ipsilateral in the cerebellum

Question 5

Describe how the cerebellum communicates with the brainstem via the cerebellar peduncles

Answer 5

• Superior cerebellar peduncle attaches cerebellum to midbrain
• Middle cerebellar peduncle attaches cerebellum to pons
• Inferior cerebellar peduncle attaches cerebellum to medulla

Question 6

What are the 6 different symptoms of cerebellar disease?

Answer 6

• Dysdiadochokinesis (can’t do rapid, alternating movements)
• Ataxia (gait abnormality)
• Nystagmus, involuntary movements of the eye)
• Itention tremor (tremor when pointing to something)
• Slurred speech
• hypotonia

Question 7

What is the basal ganglia?

Answer 7

• The basal ganglia is the area of the brain known to be involved in motor function
• It stimulates motor activity in the cerebral cortex

Question 8

Identify some important structures found in the basal ganglia

Answer 8

• Caudate nucleus - long term memory and learning (Alzheimer’s disease), control of voluntary movement
• Lentiform nucleus – made up of putamen, globus pallidus externa and globus pallidus interna
• Substantia nigra – made up of pars compacta and pars reticularis
• Subthalamic nucleus below the thalamus

Question 9

What composes the striatum?

Answer 9

Question 10

What composes the lentiform nucleus?

Answer 10

Question 11

Where is the output of the basal ganglia?

Answer 11

The output of the basal ganglia is via the thalamus

Question 12

What type of neurons are found in the striatum?

Answer 12

Most of the neurons in the striatum are GABAergic inhibitory

Question 13

Describe the structure of the substantia nigra

Answer 13

Substantia nigra is made up of pigmented neurons called the pars compacta dorsally, and a ventral strip called the pars reticularis

Question 14

What type of neurons are found in the pars compacta?

Answer 14

Dopaminergic neurons found in substantia nigra pars compacta

Question 15

The circuitry of basal ganglia is arranged in direct and indirect pathways to the thalamus.

Describe the layout and components of the direct pathway

Answer 15

• Direct pathway is overall excitatory to thalamus and cortex without dopamine
• Addition of dopamine from SNc encourages stimulation of cortex

Question 16

The circuitry of basal ganglia is arranged in direct and indirect pathways to the thalamus.

Describe the layout and components of the indirect pathway

Answer 16

• Indirect pathway is overall inhibitory to thalamus and cortex without dopamine
• Addition of dopamine from SNc promotes stimulation of cortex

Question 17

Identify four symptoms of basal ganglia disorders

Answer 17

• Abnormal motor control
• Altered posture
• Altered muscle tone
• Dyskinesia

Question 18

What is Parkinson’s disease?

Answer 18

• Parkinson’s disease is a chronic, progressive movement disorder characterised by a triad of

bradykinesia (slow movements due to reduced cortical excitation)

tremor (not sure)

rigidity (lack of coordination between muscles)

hypophonia (bradykinesia of larynx and tongue)

• It is caused by the degeneration of the substantia nigra causes deficiency of dopamine

Question 19

Describe the effect of Parkinson’s on the direct pathway of the circuitry of the basal ganglia

Answer 19

• In Parkinson’s, there is a deficiency in dopamine
• Hence, there is less dopamine to stimulate the direct pathway leading to less inhibition of the inhibition on the thalamus

Question 20

Describe the effect of Parkinson’s on the indirect pathway of the circuitry of the basal ganglia

Answer 20

• In Parkinson’s, there is a deficiency in dopamine
• Hence, there is less dopamine to inhibit the indirect pathway so there is more inhibition on the thalamus

Question 21

Identify the three cardinal symptoms of Parkinson’s disease

Answer 21

• Resting tremor
• Bradykinesia
• Hypertonia (rigidity)

Question 22

Identify five other associated features of Parkinson’s disease

Answer 22

• Hypophonia
• Reduced facial expression
• Micrographia
• Dementia
• Depression

Question 23

What is Huntington’s disease?

Answer 23

- Huntington’s disease is an autosomal dominant, progressive neurodegenerative disorder associated with cell loss within the basal ganglia and cortex

early stage is to do with loss of inhibitory projections from striatum to GPe = hyperkinetic features

• The onset of disease is around 30-50 years

Question 24

Illustrate the effect of Huntington’s on the indirect pathway of the circuitry of the basal ganglia

Answer 24

Question 25

Identify 5 symptoms of Huntington’s disease

Answer 25

• Chorea → dance like movements
• Dystonia → uncomfortable contractions of agonists and antagonists
• Incoordination
• Cognitive decline
• Behavioural difficulties

Question 26

What is hemiballismus?

Answer 26

- Hemiballismus is a rare movement disorder associated with dysfunctional contralateral subthalamic nuclei (inhibits thalamus via GPi) damage

• It results in unilateral abnormal movement and is often secondary to sub-cortical stroke

Question 27

Illustrate the effect of hemiballismus on the indirect pathway of the circuitry of the basal ganglia

Answer 27

Question 28

what does the globes pallidus consist of

Answer 28

internal and external segment

Question 29

what two structures form the lentiform nucleus

Answer 29

• putamen
• globus pallidus

Question 30

what structure does the basal ganglia use to communicate with the motor Cortex?

Answer 30

thalamus, increased thalamus activity will increase cortical activity

Question 31

what is the function of the basal ganglia?

Answer 31

→ determines most appropriate set of movements and order of movements:
→ compromised of the indirect and direct pathway

→ Basal ganglia: appropriate movements

→ cerebellum: appropriate order

Question 32

what does the direct pathway do?

Answer 32

→ reinforces appropriate movements → excitatory to thalamus to stimulate the cortex

1. Substantia nigra releases dopamine to stimulate putamen
2. double inhibition (GABA) via GPi and thalamus
3. stimulates thalamus
4. glutamate stimulate the cortex

black arrow = inhibition purple = stimulate blue bubble = grey mater arrows = white matter/ axons

Question 33

what Is the role of the indirect pathway

Answer 33

→ edits out inappropriate movements → inhibits the motor cortex

1. overal STN is stimulated
2. this excites GPi (globus pallidus internal segment)
3. this then inhibits the thalamus
4. reduces cortex

Question 34

what type of receptors are involved in the direct and indirect pathway

Answer 34

excitatory D1 receptors

inhibitory D2

Question 35

what are the inputs and outputs of the cerebellum and how does this effect its signs of damage

Answer 35

inputs: ipsilateral spinal cord and contralateral sensory cortices
output: contralateral motor cortex
damage: ipsilateral signs of cerebellar damage due to decussation of corticospinal pathway

Question 36

signs of cerebellar disease

Answer 36