6a.) Movement Disorders & Basal Ganglia Flashcards
What are the basal ganglia?
Regions of grey matter situated deep to cortex in cerebral hemispheres and in midbrain
State the basal ganglia
- Caudate nucleus
- Putamen
- Globus pallidus
- Subthalamic nucleus
- Substantia nigra pars compacta
Where is the caudate nucleus found?
C shaped nucleus lining the/lying lateral to the lateral ventricle
Wher is the globus pallidus found?
Immediately medially (squished close together with) to the putamen
Where is the putamen found?
Lateral to the globus pallidus (but also squished against it) and connected to caudate nucleus by grey matter bridges
Where is the substantia nigra found?
Midbrain (mickey mouse’s eyebrows)
Where is the subthalamic nucleus found?
Inferior to thalamus
State the two regions of the substantia nigra
- Substantia nigra pars compacta (more dorsal)
- Substanita nigra pars reticulata (more ventral)
Which basal ganglia is a source of dopamine in the midbrain?
Substantia nigra pars compacta (SNc)
Which two basal ganglia make up the striatum?
Caudate and the putamen
Which two basal ganglia make up the lentiform nucleus?
Putamen and globus pallidus
Is the striatum (made up of caudate nucleus and putamen) functionally related?
Yes
*Caudate & putamen were originally a single structure however axons of the corticospinal system descended down and punctured through causing them to become partially separted (still connected by grey matter bridges)- this is why they are called the striatu due to their striated appearance
Are the structures in the lentiform nucleus (putamen & globus pallidus) functionally related?
No, they are structurally related but NOT ANATOMICALLY related
State the two segments of the globus pallidus
- Internal segment
- External segment
Where does the striatum receive input from?
- Substantia nigra compacta
- Cortex
The basal ganglia communicate with the motor cortex via the…..?
Thalamus
*Can think of thalamus as the bouncer/door man- to talk to the cortex you have to go through the thalamus
The thalamus is always excitatory/inhibitory on the cortex
Which one?
Excitatory
Discuss the role of the basal ganglia
Their role is unclear however we think that they have a role in reinforcing appropriate movements and removing inappropriate movements e.g. to pick up a cup of tea, you need to do certain movemtns such as finger flexion (finger extension wouldn’t allow you to pick up the cup). There are two pathways:
- Direct pathway: faciliates appropriate movements (excitatory to the motor cortex)
- Indirect pathway: inhibits inappropriate movements (inhibitory to the motor cortex)
Describe the role of dopamine in the basal ganglia and their relations/functions with the motor cortex
Dopamine facilitates movements by exciting the motor cortex:
- Dopamine excites the direct pathway by activating excitatory D1 receptors on striatal neurones in the direct pathway
- Dopamine inhibits indirect pathway by activating inhibitory D2 receptors on striatal neurones in the indirect pathway
What is the main role of the basal ganglia?
Stimulate motor cortex
Which side of cortex do basal ganglia regulate?
Basal ganglia regulate the ipsilateral cortex
Explain the pathophysiology of P
Chronic and progressive movement disorder caused by degeneration of dopaminergic neurones in the substantia nigra compacta; hence, the dopamine-driven facilitation of movement via both pathways (direct and indirect) is lost.
State, and explain, 8 symptoms of Parkinsons disease
- Tremor: unclear mechanism but may be due to dysfunction of indirect pathway which would usually supress unwanted movements
- Rigidity: uknown mechanism, may be related to lack of coordination between agonists and antagonists
- Bradykinesia: slow movements due to loss of cortical excitation
- Hypophonia: quiet speech due to bradykinesia of layrnx and tongue
- Decreased facial movement/mask like facies: bradykinesia of face
- Micrographia: small handwriting due to bradykinesia in hands
- Dementia: possible progression of currently unknown causative agent e.g. protein aggregates
- Depression: basal ganglia also have role in cognition and mood
What type of tremor is seen in Parkinsons?
Pill rolling tremor
Describe the gate of someone with Parkinson’s disease
Parkinsonian (also known as festinating) gait:
- Slow to start
- Then will shuffle
- Slow/find it difficult to stop
- Slow to turn
- Flexion of trunk/limbs/neck
What type of rigidity is seen in Parkinsons disease?
Lead pipe rigidity
State the inheritance pattern of Huntington’s chorea
Autosomal dominant
At what age is Huntingtons chorea onset?
Early onset at about 30-50 years old
Describe the pathophysiology of Huntington’s chorea
Progressive degeneration of neurones in brain. The early stages are asscoiated with loss of inhibitory projections from striatumto GPe (globus pallidus external segment). This leads to hyperkinetic features because we have lost inhibition to the thalamus
State, and explain, four symptoms of Huntington’s chorea
- Chorea: dance like movements due to increased motor cortex activation
- Dystonia: uncomfortable contractions of agonists and antagonists simultaneously leading to odd postures caused by overactivity in agonist/antagonist muslces and loss of coordination between these
- Loss of coordination: similar to above (idea that lost coordination of agonists and antagonists)
- Cognitive decline and behavioural disturbances: basal ganglia have role in higher metnal functions
What is hemiballismus? (include its pathophysiology)
Rare movement disorder caused by damage to the subthalamic nucleus which normally inhibits the thalamus via GPi; it causes unilateral explosive (ballistic) movements
What are ballistic movements?
Ballistic movement can be defined as muscle contractions that exhibit maximum velocities and accelerations over a very short period of time. They exhibit high firing rates, high force production, and very brief contraction times.
State one possible cause of hemiballismus
Sub-cortical stroke (lacunar infarct)
Does hemiballismus affect both sides?
No, affects one side; the side contralateral to the damaged subthalamic nucleus
Do basal ganglia lesions affect the contralateral or ipsilateral side? Discuss.
- Basal ganglia regulate the ipsilateral cortex; however, the motor cortex regulates the contralteral muscles (as our motor corticospinal tracts decussate). Hence, unilateral basal ganglia lesions will affect the contralateral side
- *NOTE: unilateral basal ganglia lesions are rare; often basal ganglia lesions are bilateral due to neurodegeneration*
Describe the anatomy of the cerebellum
- Two cerebellar hemispheres
- Midline vermis separates the two hemispheres
Describe which part of body each of the following parts of the cerebellum deals with:
- Vermis
- Hemispheres
- Vermis: trunk
- Hemispheres: ipsilateral side of body
Broadly, what is the role of the cerebellum in motor function?
Remember, basal ganglia determine what is appropriate.
- Cerebellum looks at current position of limbs and determines an appropriate sequence to conduct motor plan in
- “sequencing and coordination of movements”
How does the cerbellum communicate with the rest of the CNS?
Cerebellar peduncles
How many cerebellar peduncles are there?
Name each one and state what each one connects with?
- Superior cerebellar peduncle: midbrain
- Middle cerebellar peduncle: pons
- Inferior cerebellar peduncle: medulla
Where is the cerebellum in relation to the 4th ventricle?
Explain how cerebellar lesions can cause hydrocephalus?
Occlude 4th ventricle- impaired drainage of CSF
Basal ganglia and cerebellum work together; true or false?
True
Why does the cerebellum need vast sensory inputs from proprioceptive neurones and sensory cortices?
In order to determine the best motor sequence, it needs to know the current position of the limb
Describe the sensory inputs the cererbellum
- Sensory input from ipsilateral spinal cord
- Sensory input from contralteral sensory cortices
State, and explain, 6 signs of cerebellar disease
*THINK DANISH
- Dysdiadochokinesis:difficulty with rapidly alternating movements (presumabley due to proble with sequencing pronation-supination-pronation etc..)
- 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 muslces
- Intention tremor: tremor that worsens as target is approached
- Slurred speech (dysarthria): caused by malcoordination of laryngeal and tongue musculature
- Hypotonia: unclear mechanism
Alongside the 6 signs of cerebellar disease, what symptoms may a patient with cerebellar disease present with?
Vomitting, vertigo, difficulty walking
How may an occlusion of the three cerebellar arteries present?
Present similar to a cerebellar lesion:
- Dysdiadochokinesis
- Ataxia
- Nystagmus
- Intention tremor
- Slurred speech (dysarthria)
- Hypotonia
What kind of reflexes may someone with a cerebellar lesion have?
Pendular reflexes due to hypotonia
Describe why cerebellar lesions cause ipsilateral signs of cerebellar disease
- Cerebellum receives sensory input from ipsilateral spinal via dorsal spinocerebellar tract (regarding current position of limbs)
- Cerebellum also receives sensory input from contralateral cortex via the cortico-pontine pathway and the pontocerebellum pathway- regarding what the motor cortex proposes to do (allowing the cerebellum to determine an appropriate sequence)
- Cerebellum hemisphere projects back to contralateral cortex (with a proposed sequence of actions)
- Motor fibres from primary motor cortex project to appropriate muscle fibres via the lateral corticospinal tract- which decussates in medulla
- Since information from cerebella hemisphere has crossed midline to twice, cerebellar disease has signs on ipsilatera side
Describe lateralisation of the cerebellum
Explain, using a diagram, why basal ganglia lesions present on contralateral side
Idea that inputs to basal ganglia come from ipsilateral cortex and outputs from basal ganglia go to ipsilateral cortex. Then lateral cortical spinal tract decussates so symptoms are on contralateral side
