Flashcards in Basal Ganglia and Cerebellum Deck (61):
Do the basal ganglia modify the signals of upper and motor neurones?
No, they only modify the signals from upper motor neurones, they have no direct connection to lower motor neurones.
Which part of the brain is the cerebellum part of?
What are the folds on dorsal surface of the cerebellum called?
Folia - to give the cerebellar cortex a large surface area.
What is the white matter of the cerebellum called?
What are the two functions of the cerebellum?
Comparator functions - detecting "motor error" (the difference between the intended movement and the actual movement carried out), detecting discrepancies and sending feedback to the thalamus, so the movement can be corrected and coordinated
Motor memory - storing learned movements, any complex skill that becomes automatic after time and practice e.g driving a car
What are the three major sections of the cerebellum, based on the source of the input?
Spinocerebellum - input direct from spinal cord
Cerebrocerebellum - inputs from cerebral cortex
Vestibulocerebellum - (includes nodulus and floculus) inputs from vestibular nuclei in brainstem
What is the function of the cerebrocerebellum?
Regulates highly skilled movements involving complex sequences of movements e.g speech
What is the function of the spinocerebellum?
The central part (vermis) is involved in movements of the axial (trunk) muscles.
The lateral parts are involved in movements of the distal muscles (e.g limbs).
What is the function of the vestibulocerebellum?
Involved in movements controlling posture and balance.
What is the superior cerebellar peduncle for?
Transmits neurones between the cerebellum and midbrain, it is entirely efferent (output of cerebellum), so carries the contralateral dentatorubrothalamocortical tract.
What is the middle cerebellar peduncle for?
It transmits neurones between the cerebellum and pons. It is entirely afferent, so is where the cerebellum receives inputs.
What is the inferior cerebellar peduncle for?
It transmits neurones between the cerebellum and medulla oblongata. It is a mixture of afferent and efferent pathways, it is where the cerebellum receives contralateral input from the inferior olive (climbing fibres) and also ipsilateral information from the spinal cord and vestibular nuclei.
What are the three inputs received by the cerebellum?
1) Motor inputs - from motor cortex to pontine nuclei of relay neurones, where they decussate to reach cerebellum through contralateral middle cerebellar peduncle
2) Sensory inputs - ipsilaterally received from muscle proprioceptors, vestibular nuclei, visual and auditory through the inferior cerebellar peduncle, conveying information about position and motion
3) Inferior olive in the medulla oblongata - transmits information to contralateral hemisphere through inferior cerebellar peduncle, conveys modulation on timing, learning, memory
What is the major way information is transmitted out of the cerebellum?
Major output structures are the deep cerebellar nuclei. Information is sent from the deep cerebellar nuclei to the cortex via the thalamus, providing the feedback loop for the comparative functions of the cerebellum.
The information is sent contralaterally through the superior cerebellar peduncle.
Which of the deep cerebellar nuclei relays information from the vestibulocerebellum?
Fastigial nucleus (or direct to spinal cord) for balance and eye movement.
Which of the deep cerebellar nuclei relays information from the central spinocerebellum?
Fastigial nucleus, for motor execution of the axial (proximal/trunk) descending systems.
Which of the deep cerebellar nuclei relays information from the lateral spinocerebellum?
Interposed nucleus, for motor execution of the distal (limbs) descending systems.
Which of the deep cerebellar nuclei relays information from the cerebrocerebellum?
Dentate nucleus, to the motor and premotor cortex for motor planning.
What are the three layers of the cerebellar cortex?
Molecular, Purkinje, Granule.
What are the 2 input cells in the cerebellar cortex?
Climbing fibre (from inferior olive)
Mossy fibre (from all other inputs)
What are the output cells of the cerebellar cortex?
Purkinje cells (have large cell bodies in Purkinje layer and large branched dendrites in molecular layer)
What are the interneurones in the cerebellar cortex?
Granule cells, basket cells, stellate cells, golgi cells.
What are parallel fibres?
Parallel fibres are the branches of Granule cells in the molecular layer, which run parallel to the cerebellar cortex, and synapse with the dendrites of Purkinje cells.
What is the function of climbing fibres?
They carry input from the inferior olive. They carry error signals so when the movement fails to meet the target/expectations, they can correct it by altering the effectiveness of the parallel inputs to the Purkinje cells (inhibitory).
So they are part of the comparative function, and modify outputs of the Purkinje cells to adjust movements.
What is the function of mossy fibres?
They carry inputs from the cerebra cortex via pontine nuclei and the middle cerebellar peduncle, and inputs from the spinal cord and vestibular nuclei via the inferior cerebellar peduncle. They synapse with granule cells in the Granule layer.
What is the function of granule cells?
To send information to Purkinje cells via parallel fibres.
What is the neurotransmitter released by Purkinje cells at their synapse with the deep cerebellar nuclei?
Gamma aminobutyric acid (GABA)
`Will movement errors be contralateral or ipsilateral to the damaged hemisphere of the cerebellum?
Ipsilateral (because the cerebellum receives ipsilateral input from muscle proprioceptors, vestibular nuclei, auditory and visual)
What effects result from damage to the vestibulocerebellum (nodulo-flocular lobe)?
Disturbances of balance and eye movements
What effects occur from damage to the central spinocerebellum?
Postural and gait ataxia (wide based gait with small shuffling movements)
What effects occur from damage to the lateral spinocerebellum?
Upper limb ataxia and dysarthria
What effects occur from damage to the cerebrocerebellum?
Impairments in highly skilled sequences of learned movements.
What is cerebellar ataxia?
Jerky, imprecise, uncoordinated movements
What is dyssynergia?
Loss of synergistic multi-jpont movements, so joints have to be moved one at a time.
What is dysmetria?
Inability to judge distances, so movements overshoot e.g past-pointing
What is dysdiadochokinesis?
Inability to perform rapid alternating movements e.g tapping the table with alternating hands
What is intention tremor?
Shaking when trying to move but no tremor when at rest (also seen with lesion in the rubrospinal tract)
What is ataxic dysarthria?
Which part of the cerebellum is particularly damaged by alcohol abuse, and what are the effects caused?
Anterior cerebellum, which includes part on lateral spinocerebellum concerned with lower limbs.
Leads to wide staggering gait, but little impairment of arm or hand movements.
Why don't we laugh when we tickle ourselves?
Cerebellum acts as a gate and alerts primary somatosensory cortex to planned movement, so it dampens down any sensations caused by the movement, so the brain knows it's just you tickling yourself and doesn't get excited.
What are the components of the basal ganglia?
Putamen, globus pallidus pars internal and pars external, caudate nucleus, substantia nigra, subthalamic nucleus
What are the two parts of the substantia nigra, and which is input and which is output?
Pars compacta = input
Pars reticulata = output
What makes up the striatum (input zone)?
Caudate nucleus and putamen
Which three parts of the basal ganglia make up the output zone?
Globus pallidus, subthalamic nucleus, substantia nigra pars reticulata
(The most lateral nuclei are the input zone and the deeper nuclei are the output zone)
What is the function of the basal ganglia?
Selection and maintenance of voluntary movements.
They suppress unintended movement due to constitutive firing of neurones, by tonic inhibition.
They keep intended movement going.
They modulate the initiation and termination of motor commands.
(They also have a role in non motor functions like cognition, working memory, attention)
What are the three pathways by which the basal ganglia receive inputs, and what are the neurotransmitters?
1) Corticostriatal pathway - inputs from cerebral cortex to striatum, neurotransmitter is glutamate
2) Nigrostriatal pathway - inputs from pars compacta of substantia nigra to striatum, neurotransmitter is dopamine
3) Medium spiny neurones - neurones in the striatum that receive inputs
What are the two places where outputs of the basal ganglia go?
1) cerebral cortex via the thalamus
2) eye movements go to the superior colliculi
What are the two pathways forming the corticostriatal loops?
1) Direct pathway - D1 receptors in striatum activated, output via globus pallidus internal segment, tonic inhibition of thalamus lifted
2) Indirect pathway - D2 receptors in striatum activated, output via globus pallidus external segment and subthalamic nucleus, thalamus is tonically inhibited
What is the direct pathway of the basal ganglia?
Motor cortex sends excitatory signal to striatum so striatum increases inhibition of globus pallidus internal segment. Dopamine released from the substantia nigra binds to D1 receptors in the striatum and increases the inhibition of the globus pallidus internal segment by the striatum, so the tonic inhibition of the thalamus is lifted, the cortex is excited and movement is initiated.
What effect does the substantia nigra have on the direct and indirect pathways?
Stimulates the direct pathway, inhibits the indirect pathway.
What is the indirect pathway of the basal ganglia?
Motor cortex sends excitatory signals to striatum which activates inhibitory neurones from striatum to globus pallidus external segment. The striatum inhibits the globus pallidus external segment, which lifts the inhibition on the globus pallidus internal segment and on the subthalamic nucleus. The subthalamic nucleus excites the globus pallidus internal segment which inhibits the thalamus. The cortex is not excited and movement is inhibited.
The substantia nigra releases dopamine which activates the D2 receptors of the striatum and this decreases the inhibition of the globus pallidus external segment by the striatum.
What sort of movement disorder is Parkinson's?
Hypokinesia - paucity of movement
What is the global prevalence, and peak onset age, of Parkinson's?
Global prevalence = 1 in 500
Peak onset age = 60
What are the four clinical characteristics of Parkinson's?
Tremor of hands (with periodicity)
Rigidity of muscles
What is the neuropathology of Parkinson's disease?
The degeneration of the dopaminergic neurones in the substantia nigra that project to the striatum (nigrostriatal pathway), decreasing dopamine availability.
This means the stimulation of the direct pathway is reduced and the inhibition of the indirect pathway is reduced, so the tonic inhibition on the thalamus is increased so there is difficulty in starting and stopping movements.
What are the five treatments used for Parkinson's?
1) Levodopamine (L-dopa) - increases systemic dopamine but can can cross BBB so increases dopamine in the neurones of the substantia nigra that are still alive
2) Dopamine agonists to activate D1 and D2 receptors in the striatum (side effects = sudden sleepiness)
3) Foetal cell transplants - mesencephalic cells (stem cells) transplanted into putamen
4) Deep brain stimulation - implanted electrode to inactivate the globus pallidus or subthalamic nucleus or thalamus using high frequency stimulation
5) Surgery to remove part of the globes pallidus (pallidotomy) or thalamus (thalamotomy)
What are the side effects of L-dopa?
Dyskinesia, drug resistance, psychosis.
What is the cause of Huntingdon's disease?
It's a genetic disorder, a mutation on chromosome 4 means the output neurones of the striatum to the globus pallidus external segment are lost, so cortical motor areas are over stimulated.
What type of disorder is Huntingdon's and what are the symptoms?
It is a hyperkinesia disorder, and the symptoms are excessive uncontrollable jerky movements (chorea).
How do the drugs used to treat Huntingdon's and Hemiballismus work?
They deplete dopamine.