Basal ganglia and cerebellum Flashcards
As well as modulating motor control, what function are basal ganglia and cerebellum thought to be linked to?
Learning
Where are the basal ganglia located?
In the white matter in the middle of the brain
What structures does the basal ganglia consist of?
Striatum, globus pallidus, substantia nigra and subthalamic nucleus
What does the striatum consist of
Caudate and putamen
What are the two segments of the globus pallidus
External (GPext) or lateral segment
Internal (GPint) or medial segment
What are the two parts of the substantia nigra?
Consists of the pars compacta (SNc) and pars reticula (SNr)
What is the function of the basal ganglia?
Planning and programming movement
Elaborating associated movements (swinging arms when walking)
Smoothness of complex action
Involved in moderating and coordinating movements
Describe the start of the circuit of basal ganglia
They start in the cerebral cortex (primary motor, premotor, supplementary, somatosensory and parietal) and these neurones go to the striatum (caudate and putamen)
What are the two pathways of the circuits after the striatum?
The direct pathway and indirect pathway
What is the direct pathway?
Putamen -> Globus pallidus internal segment and substantia nigra
What is the indirect pathway?
Putamen -> Globus pallidus external segment -> Subthalamic nucleus -> Globus pallidus internal segment
What effect does the direct pathway have on the motor cortex?
Excitatory
What effect does the indirect pathway have on the motor cortex?
Inhibitory
What modulates the functions of the pathways?
Nigro-striatal pathway
Where do these projections go once they exit the basal ganglia?
Thalamus then they go back to the cortex to the supplementary motor area and primary motor area
How are the basal ganglia also involved in cognitive function?
There are cortical loops that go through the basal ganglia and connects the basal ganglia with the prefrontal association cortex and limbic cortex. They’re involved in selecting and enabling various cognitive, executive and emotional programmes that are stored in these cortical areas
What causes Parkinson’s disease?
Neuronal degeneration of the Substantia Nigra Pars Compacta, it is caused by the progressive depletion of dopamine neurones
When do clinical signs appear in Parkinson’s?
When about 80% of the dopamine cells in the substantia nigra have died
When there is loss of nigra-striatal dopaminergic neurones in the caudate and putamen which leads to a loss of connection between the striatum and substantia nigra pars compact, what happens?
Excitation of the motor cortex is reduced
What are the signs of parkinson’s disease?
Akinesia, parkinsonian gait and stooped posture
What is akinesia?
When it is difficult to initiate movements because they’ve lost the feedback between the basal ganglia and cortex
What is Huntington’s disease and what causes it?
It is a neurodegenerative disorder that is caused by an abnormality on chromosome 4, it is autosomal dominant.
What does the abnormality on chromosome 4 cause?
Degeneration of GABAnergic neurones in the striatum which means that excitatory effect of the direct pathway is no longer controlled by inhibitory pathway
What are the main sign’s of Huntington’s?
Choreic movements- Rapid, jerking, involuntary movements
Which parts of the body are affected first in Huntington’s?
Hands and face
What are the three horizontal lobes of the cerebellum?
Anterior, posterior and flocculonodular
What are the three coronal zones of the cerebellum?
Vermis- in the middle
Intermediate hemisphere
Lateral hemisphere
What are the three layers in the cerebellar cortex, starting with the most internal?
Granule cells
Purkinje cells
Molecular layer
What does the molecular layer contain?
Axons of the granule cells and dendrites of the Purkinje cells
What are the three deep nuclei in the cerebellum?
Fastigial
Interposed
Dentate
What is the fastigial nucleus involved in?
Control of balance and is connected with vestibular nuclei
What are the interposed and dentate nuclei involved in?
Both are involved in voluntary movement and are connected to the thalamus and red nucleus
What are the three sources of input to the cerebellum?
Mossy fibres- that bring information from the cerebral cortex and pons
Mossy fibres from the spinocerebellar tract
Climbing fibres from the inferior olive
What is the function of the vestibulocerebellum (flocculonodular lobe)?
Involvement with balance, posture and regulation of gait
Also involved in coordination of head movements with eye movements
What is the function of the spinocerebellum?
Coordination of speech, adjustment of muscle tone and coordination of limb movement
What is the function of the cerebrocerebellum?
Coordination of skilled movements, cognitive function, attention, processing of language and emotional control
Overall, what are the 4 main functions of the cerebellum?
Balance and posture, coordination of voluntary movement, cognitive functions and motor learning
What occurs in vestibulocerebellar syndrome?
Patients tend to lose their balance with gait ataxia and a tendency to fall
What is spinocerebellar syndrome highly associated with as a cause?
Chronic alcoholism
What occurs in spinocerebellar syndrome?
It mainly affects the legs and causes an abnormal gait or a wide stance
What occurs in cerebrocerebellar syndrome?
It mainly affects the arms and affects coordinated movements, speech becomes very slow and hesitant
What are the 5 main signs of cerebellar disorders?
Ataxia Dysmetria Intention tremor Dysdiadochokinesia Scanning speech- staccato
What is dysmetria?
Inappropriate force and distance on target directed movements
What is an intention tremor?
Increasingly oscillatory trajectory of a limb in a target directed movement
What the balls is dysdiadochokinesia?
Inability to perform rapidly alternating movements
How is intention tremor assessed clinically?
Nose-finger tracking
