Motor Control II - Role of the Cerebellum and Basal Ganglia Flashcards
What is the role of the cerebellum?
- closely involved with brainstem mechanisms
- control of muscle tone
- sensorimotor coordination
- motor learning
What is the role of the basal ganglia?
- integrated of sensory and motor information
cortex –> basal ganglia –> cortex loop (via thalamus)
Neither the cerebellum nor basal ganglia project……
beyond the brain
What 2 motor disorders are associated with the basal ganglia?
Parkinson’s Disease
Huntington’s Disease
What are the 3 anatomical and functional components of the cerebellum? In what regions of the cerebellum are they found?
- spino-cerebellum (medial region of cerebellum)
- vestibulo-cerebellum (caudal region of cerebellum)
- cerebro(ponto)-cerebellum (lateral hemispheres)
Describe the connections and functions of the spino-cerebellum
- sensory input from the spinal cord
- output to the reticular formation and red nucleus
- then to motor cortex
- then output to spinal cord
- control of axial musculature and posture
What is the result of damage to the spino-cerebellum?
- hypotonia
- ataxia (unsteady, staggering gait)
- dysmetria (inaccurate termination of movement and ‘intention tremor’
Describe the connections and functions of the vestibulo-cerebellum
- input from and output to vestibular nucleus
- contro over posture/balance, also eye movement
What is the result of damage to the vestibulo-cerebellum?
slow saccades = fast tracking ocular movement impaired
nystagmus = due to failed vestibulo-oculomotor integration
ataxia = unsteady, staggering gait
Describe the connections and functions of the cerebro(ponto)-cerebellum
- an intracerebral motor loop
- cortex–>pons–>cerebellum –> dentate nucleus –> ventrolateral thalamus –> cortex
- instructs M1 regarding movement direction, timing and force
- compares intended movements with actual movements and sends compensatory instructions to M1
What is the result of damage to the cerebro(ponto)-cerebellum?
- incoordination/ataxia
- dysmetria - intention tremor - inaccruate termination of movement
- asynergy - uncoordiatned agonist and antagonist muscles
- dysarthria - inarticulate speech - poor oesophageal muscular control
List the components of the circuitry of the cerebellar cortex
parallel fibres purkinje cell granule cell layer white matter (mossy fibres, climbing fibres) ---> deep cerebellar nuclei
What are the inputs into the circuitry of the cerebellar cortex?
- climbing fibres input from inferior olive - excitatory and act on Purkinje cells
- mossy fibres from brainstem nuclei - indirectly excite Purkinje cells via parallel fibres of Granule cells
What are the outputs of the cerebellar cortex circuitry?
only purkinje cells - project to deep cerebellar nuclei
What do deep cerebellar nuclei do?
- compare input from mossy and climbing afferent input
from mossy and climbing afferent input
before = via collaterals form axons to purkinje cells
after = cerebellar processing via inhibitory purkinje cell output
–> error signal
What is the mechanism behind motor memory?
- granule cell parallel fibre - purkinke cell synapses
- shows use dependent plasticity
- thought to be involved in motor learning
What are the 4 functions of the cerebellum?
1, regulates posture indirectly by adjusting output of major descending motor pathways
- acts as a comparator identifying and correcting discrepancies between intended movement actual movement
- acts as a timer, sequencing motor activation resulting in smooth performance
- role in motor memory and in instigating learned motor sequences when appropriate
What are the basal ganglia?
Which nuclei are included?
- a group of associated subcortical nuclei
Striatum = putamen, caudate nucleus, nucleus acucmbens
Globus Pallidus
Substantia Nigra
Subthalamic Nuclei
Draw the basic basal ganglia circuit
Colour code
see lecture
Describe the direct and indirect pathways
draw diagram and explain inhibition/disinhibition
DIRECT = acts to facilitate movement
INDIRECT = acts to inhibit movement
What is the neurotransmitter for the:
- excitatory pathways
- inhibitory pathways
- modulatory pathways
- excitatory pathways = GLUTAMATE
- inhibitory pathways = GABA
- modulatory pathways = DOPAMINE
What is the effect of dopamine on the
- direct pathway
- indirect pathway
DIRECT
- dopamine acts on excitatory D1 receptors to further reduce BG output and facilitate movement
INDIRECT
- dopamine acts on inhibitory D2 receptors, reduces Stn activity and BG output and also facilitates movement
What leads to motor dysfunction?
- imbalance between the direct and indirect pathways
Give examples of hypo and hyperkinetic disorders
Hypokinetic - Parkinson's Hyperkinetic - Huntington's - Hemiballism - Tardive Dyskinesia
What affect does Parkinson’s have on the basal gala pathway?
- dopamine loss in nigro-striatal pathway
- excessive inhibition of thalami-cortical pathway
- driven by increases in activity in the sub thalamic nucleus
What affect does Huntington’s have on the basal ganglia pathway?
- loss on striatal output neurones in indirect pathway
- suppression of STN
- predominance of direct pathway
- decrease BG output
- overactive thalamocortical pathway
- involuntary movement
What are the symptoms of the Parkinson’s disease
rigidity
bradykinesia
tremor
What are the symptoms of Huntingtons disease?
excessive choreiform movements
- uncontrollable, relatively rapid motor patterns distrust normal motor activity
What is the cause of hemiballism?
- damage to subthalamic nucleus (usually by unilateral intracerebral thrombosis
What is the effect of hemiballism?
violent flailing movements of limbs contralateral to damaged side
What is the cause of tardive dyskinesia?
- increased dopamine receptor sensitivity, due to long-term exposure to antipsychotic dopamine receptor antagonist drugs
What is the effect of tardive dyskinesia?
- uncontrolled movement, especially of facial and trunk muscles
