Motor Pathways: Basal Ganglia and Cerebellum Flashcards
What is the collective term given to the basal ganglia and cerebellum?
Extrapyramidal system
What is the function of the basal ganglia>
Elaborating associated movements (e.g. swinging arms when walking)
Moderating + coordinating movement (suppressing unwanted movement)
Performing movements in order
Where is the basal ganglion located?
White matter in the middle of the brain
What is the basal ganglia composed of?
Caudate nucleus
Lentiform nucleus (globus pallidus + putamen)
Subthalamic nucleus
Substantia nigra
Where do the projections go after leaving the basal ganglion structures?
To the thalamus
Then to the cortex (supplementary motor area + primary motor area = 2 regions involved in movement preparation + planning)
What causes Parkinson’s disease?
Neuronal degeneration of dopaminergic neurones that originate in the substantia nigra + project to the striatum
State the 5 main motor signs of Parkinson’s disease.
Bradykinesia: slow movement Akinesia: difficulty initiating movements Hypomimic face: expressionless face Tremor at rest Rigidity: increase in muscle tone
Describe the Parkinsonian gait.
Walking slowly, small steps, shuffling feet, reduced arm swing
Stooped posture with head + body bent forwards + downwards
What is Huntington’s disease caused by?
Abnormality on chromosome 4 (autosomal dominant)
CAG repeat
Caused by the degeneration of GABAergic neurones in the striatum (1st the caudate, then the putamen)
What are the consequences of the pathology of Huntington’s with regards to the circuitry of the basal ganglia?
Inhibitory effect of the indirect pathway no longer keeps the direct pathway under control so the cortex will be hyperexcitable.
Patients will continuously have abnormal movements because the cortex is continuously sending involuntary commands for movements.
What are the 6 main signs of Huntington’s disease and how does the disease progress?
Choreic movements: rapid, jerky, involuntary movements of the body (hands + face affected 1st, increases over time until patients are totally incapacitated)
Speech impairment
Difficulty swallowing
Unsteady gait (due to involuntary activity)
Cognitive decline
Dementia.
State the 3 layers of the cerebellar cortex.
Granular cell layer (many small neurones involved in processing) Purkinje cells (large projecting cells with huge dendritic trees) Molecular layer (outer, not many neurones)
Describe the input to the cerebellum
Inferior olive projects to Purkinje cells via Climbing fibres
All other input to granular cells via mossy fibres + then onwards via parallel fibres
Functionally, the cerebellum can be divided in three. What are these three divisions?
Vestibulocerbellum
Spinocerebellum
Cerebrocerebellum
What is the role of the vestibulocerebellum?
Regulation of gait, posture + equilibrium
Coordination of head movements with eye movements
What are the roles of the spinocerebellum?
Coordination of speech
Adjustment of muscle tone
Coordination of limb movement
Which part of the cerebellum is part of the cerebrocerebellum?
Lateral hemisphere
What are the 5 main functions of the cerebrocerebellum?
Coordination of skilled movements Cognitive function Attention Processing of language Emotional control
State 3 syndromes caused by dysfunction of different parts of the cerebellum.
Vestibulocerebellar syndrome
Spinocerebellar syndrome
Cerberocerebellar syndrome
What are the symptoms of vestibulocerebellar syndrome?
Similar to vestibular disease
Gait ataxia
Tendency to fall (even when sitting with eyes open)
What behavioural habit is spinocerebellar syndrome associated with?
Chronic alcoholism
Describe the symptoms of spinocerebellar syndrome.
Mainly affects legs
It causes abnormal gait + a wide-based stance
Describe the symptoms of cerebrocerebellar syndrome.
Mainly affects arms + coordinated movements (tremor)
Speech becomes very hesitant + slow (staccato)
What are the 5 main signs of cerebellar disorders?
Ataxia: general impairments in movement coordination + accuracy
Dysmetria: inappropriate force + distance for target-directed movements
Intention tremor: increasingly oscillatory trajectory of a limb in a target directed movement (nose-finger tracking)
Dysdiadochokinesia: inability to perform rapid alternating movements
Scanning speech: staccato, due to impaired coordination of speech muscles
State a hereditary and acquired cause of cerebellar dysfunction
Hereditary – Friedreich’s Ataxia
Acquired – Multiple Sclerosis
What is the striatum composed of?
Caudate
Putamen
External global palidus
Which 3 areas in basal ganglia nuclei are commonly affected by disease?
Nigro-striatal system= PD
Striatum->Globus pallidus (int.)= HD
Subthalamic nucleus->Globus pallidus (int.)= Ballism
Describe the cerebellar output
All output from Purkinje cells via deep nuclei
