6 Disorders of the motor system and Parkinson's disease

Question 1

what structured form the lentiform nucleus?

Answer 1

globus pallidus (interna and externa) 
putamen

Question 2

what is a DAT SCAN?

Answer 2

DaTscan is a tool used to confirm the diagnosis of Parkinson’s disease. It is a specific type of single-photon emission computed tomography (SPECT) imaging technique that helps visualize dopamine transporter levels in the brain. high levels will show as red/blue. low levels as green.

Question 3

what are the basal ganglia?

Answer 3

The basal ganglia are situated at the base of the forebrain and top of the midbrain. The basal ganglia are associated with a variety of functions, including control of voluntary motor movements, procedural learning, habit learning, eye movements, cognition, and emotion.

Question 4

what are the key components of the basal ganglia?

Answer 4

caudate nucleus
putamen
globus pallidus
subthalamic nucleus

Question 5

what 2 components form the striatum?

Answer 5

the caudate and the putamen

Question 6

what is the substantia nigra?

Answer 6

The substantia nigra is a part of the midbrain. Sits deep to the cerebral peduncles. Contains dopaminergic neurones that send their axons up to the striatum in the nitro-striata pathway.

Question 7

how is the putamen connected to the caudate nucleus?

Answer 7

via grey matter bridges

Question 8

what does the striatum receive input from?

Answer 8

the cortex

substantia nigra

Question 9

what is the function of the basal ganglia?

Answer 9

Probable role in reinforcing appropriate movements and

removing inappropriate movements.

Question 10

how does dopamine facilitate movement?

Answer 10

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)

Question 11

if the substantia nigra is affected unilaterally, how will this manifest?

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 the underlying pathology in parkinsons disease?

Answer 12

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

Question 13

what are the signs and symptoms of parkinsons disease?

Answer 13

• 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 faces (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 huntingtons chorea?

Answer 14

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)

Question 15

what are the features of huntingtons disease?

Answer 15

• 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

what is hemiballismus?

Answer 16

a basal ganglia syndrome resulting from damage to the subthalamic nucleus in the basal ganglia. Hemiballismus is a rare hyperkinetic movement disorder, that is characterized by violent involuntary limb movements, on one side of the body, and can cause significant disability.

Question 17

what can cause hemiballismus?

Answer 17

Can be caused by sub-cortical stroke (lacunar infarct) causing damage to the subthalamic nucleus

Question 18

what is the structure of the cerebellum?

Answer 18

midline vermis and two laterally placed hemispheres

Question 19

how do the cerebellar hemispheres communicate with the rest of the CNS?

Answer 19

through the cerebellar peduncles

Question 20

what is the function of the different cerebellar peduncles?

Answer 20

• Superior cerebellar peduncle connects to midbrain
• Middle cerebellar peduncle connects to pons
• Inferior cerebellar peduncle connects to medulla

Question 21

why can cerebellar lesions cause hydrocephalus?

Answer 21

as the cerebellum sits above the fourth ventricle and a lesion here can occlude the cerebral aqueduct causing hydrocephalus

Question 22

what is the function of the cerebellum?

Answer 22

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.

Question 23

what inputs does the cerebellum receive?

Answer 23

cerebellum has profuse sensory inputs from

proprioceptive neurones and the sensory cortices

Question 24

what are the outputs of the cerebellum?

Answer 24

outputs are to the

contralateral motor cortex

Question 25

does damage to the cerebellum manifest ipsilaterally or contralaterally?

Answer 25

ipsilaterally as the corticospinal tract between the PMC and the cerebellar hemisphere decussates. the sensory input into the cerebellum is ipsilateral.

Question 26

what are the signs of cerebellar disease?

Answer 26

DANISH

• Dysdiadochokinesia
• Ataxia
• Nystagmus
• Intention tremor
• Slurred speech (dysarthria)
• Hypotonia

Question 27

how is the thalamus associated with the basal ganglia?

Answer 27

when the basal ganglia are communicating back with the PMC, impulses have to move through the thalamus.

Question 28

the cerebellum receives sensory input from 2 sources, what are they?

Answer 28

contralateral primary sensory cortex
ipsilateral impulse from the spino-cerebellar tract in the spinal cord. carry information from proprioreceptors in the muscles

Question 29

what is the corticospinal pathway?

Answer 29

a motor pathway running from the primary motor cortex, through the internal capsule and decussates at the medulla before travelling down the spinal cord to the level of the target muscle. Then synapses at the LMN.
chain of 2 neurones that mediate movement and behaviours.

Question 30

what is the corticostriatal pathway?

Answer 30

a pathway that starts at the primary motor cortex. projects down to the ipsilateral striatum (putamen and caudate nucleus). allows motor plan to be analysed by the basal ganglia before the results being sent back to the PMC

Question 31

what is the pallidothalamocortical pathway?

Answer 31

a pathway from the globus pallidus via the thalamus to the pmc. llows motor plan to be analysed by the basal ganglia before the results being sent back to the PM. works alongside the corticostriatal pathway to create a loop

Question 32

what is the nigrostriatal pathway

Answer 32

pathway between the substantia nigra and the striatum. substantia nigra sits in the midbrain, axon projects up to the striatum to provide a source of dopamine to the basal ganglia

Question 33

what is the corticopontocerebellar pathway.

Answer 33

allows the pmc to communicate the motor plan to the cerebellum. 1st neurones is from the pmc to the pons to synapse on a neurone of the pontine nuclei. These then decussate to the contralateral cerebellar hemisphere

Question 34

what is the cerebello-thalamo-cortico pathway?

Answer 34

neurones in the cerebellum communicate with the contralateral thalamus to send an impulse of the correct sequence of the motor plan. 2nd neurone from thalamus to the pmc.

Question 35

what is the spinocerebellar pathway?

Answer 35

collects information from muscle spindle fibres. sensory pathway travels up in the dorsal spinocerebellar tract to the ipsilateral cerebellar hemisphere

Question 36

the internal capsule is a continuation of which structure?

Answer 36

the corona radiata

Question 37

what can be found at the genu of the internal capsule?

Answer 37

the axons of the facial UMN