BASAL GANGLIA AND CEREBELLUM Flashcards
What are the functions of the cerebellum?
- Coordination of planned, voluntary multi-joint movements, balance and muscle tone.
- Comparator function: Detects difference in “motor error” i.e. between intended movement and actual movement.
- Motor memory: Stores learned movement. Consciousness to unconsciousness, e.g. riding a bicycle
describe the external structure of the cerebellum?
the dorsal surface is highly folded into folia. it is divided into 2 lobules.
where are the white and grey matter found in the cerebellum?
Grey matter – located on the surface of the cerebellum. It is tightly folded, forming the cerebellar cortex.
White matter – located underneath the cerebellar cortex.
what are the 3 functional divisions of the cerebellum?
cerebrocerebellum (dentate nuclei)
spinocerebellum (interposed and fastigial nuclei)
vestublocerebellum (fastigi nuclei or direct)
describe the cerebrocerebellum?
Inputs come from cerebral cortex. Involved in the regulation of highly skilled movements. Both on lateral sides
describe the spino-cerebellum?
Recieves direct input from spinal cord. Lateral part involved in movements of distal muscles. Central part (vermis) concerned with movements of proximal muscles.
describe the vestibulocerebellum?
Includes nodulus and flocculus. Receives inputs from vestibular nuclei in brainstem. Involved in movements underlying posture and balance.
how is the cerebellum attached to the brainstem?
by the cerebellar peduncles at the level of the pins
which pathways do the superior, middle and inferior cerebellar peduncles take?
superior= efferent middle= afferent inferior= afferent and efferent
describe the main motor inputs to the cerebellum?
the motor inputs from the cerebral cortex bring information into the cerebellum via the pontine nuclei which then project over the cerebellar midline via the middle cerebellar peduncle over to the opposite cerebellar hemisphere
describe the main sensory inputs to the cerebellum?
Sensory inputs come from the same side of the body, they ascend from the spinal cord and vestibular nucleus
(and visual, auditory, proprioceptor systems).
describe the motor input to the cerebellum via the red nucleus?
what is the function?
Motor inputs from the cerebral cortex project to the red nucleus which, in turn, projects to the inferior olive. The outputs cross over the midline and project to the cerebellar cortex.
modulatory e.g. timing, learning and memory
describe the main outputs from the cerebellum?
The cerebellar cortex contains the neurons which then project to the deep cerebellar nuclei. The neurons then cross the midline and project up to the thalamus via a superior cerebellar peduncle and they then synapse with neurons which project up to the primary motor and pre-motor cortex.
what are deep cerebellar nuclei?
Major output structures embedded in deep white matter. Relay cortical cerebellar information to motor cortex and brainstem to make corrections in movement.
what are the 3 types of deep cerebellar nuclei?
fastigial (medial), 2 interposed and a dentate nucleus (lateral)
what type if disorder is Parkinson’s?
a hypokinesia disorder which causes a reduction in moveemnt
disease is progressive
what is the peak onset age for Parkinson’s?
60 years old
what is the cause of parkinsons?
it is largely idiopathic but can be genetic
what are the clinical characteristics of parkinsons?
trap tremor of hands rigidity of muscles akinesia postural probelsm
what is the neuropathology of parkinson’s?
Degeneration of neurons in substantia nigra that project to striatum. Decrease in dopamine availability. Results in decreased activity of the direct pathway and increased activity of indirect pathway= reduction of movement.
what would the post-mortem of a parkinsons patient show?
Degeneration of pigmented cells (dopamine-utilising neurons) in substantia nigra pars compacta.
what are the 4 treatment options for parkinsons?
L-DOPA
dopamine agonists
foetal cell transplants
deep brain stimulation/surgery
how can dancing and music help with parkinson’s?
It enhances audio perception and movement synchronization
Rhythm in music acts as external cue, replacing internal timing function that is impaired in Parkinson’s disease this helps compensate for loss of control by the extrapyramidal system.
what is L-DOPA?
levodopa is a precursor of dopamine. . Boosts dopamine levels in substantia nigra neurons still alive.
what are the side effects of L-DOPA?
drug resistance, involuntary movements (dyskinesia), psychosis
what do dopamine agonist do?
what is a side effect?
Stimulate postsynaptic dopamine receptors in striatum. But many side effects, e.g. sudden sleepiness.
what is foetal cell transplant?
Transplantation of foetal mesencephalic cells (stem cells) into putamen. Similar to dopamine replacement therapy. Some success. Ethics questionable.
what is deep brain stimulation?
: Implanted electrode to inactivate the globus pallidus / Subthalamic nucleus / thalamus using high frequency stimulation
what is deep brain surgery?
Remove part of globus pallidus (pallidotomy) or thalamus (thalamotomy).
other than parkinsons, what are 2 common neuropathology’s affecting the basal ganglia?
huntingtons
hemibalismus
outline Huntington’s disease?
• Genetic disorder (chromosome 4, Huntingtin gene). Loss of output neurons of striatum. This reduces the inhibition of the subthalamic nucleus and reduced excitation of globus pallidus internal segment. This leads to a decrease in tonic inhibition of the thalamus. Results in cortical motor areas being over-activated.
outline hemiballismus?
Rapid, flinging and violent movements of limbs (ballismus) on one side of body (hemi).
Neuropathology: Damage to subthalamic nucleus
Treatment: Similar to Huntington’s – deplete dopamine levels
what are the 3 layers of the cerebellum?
granule cell layer (deepest), purkinje cell layer and molecular layer (most superficial)
what are the 2 types of axons that enter the cerebellum?
mossy fibres and climbing fibres
where do climbing fibres arise from?
inferior olivary nucleus
where do mossy fibres arise from?
all cerebellar inputs other than inferior olivary nucleus e.g. motor cortex and spinal cord
what are the interneurones within the cerebellum?
granule cells, stellate cells, Golgi cells and basket cells
where do granule cells received input from?
mossy fibres
what are the output cells from cerebellum?
purkinje cells
where do purkinje fibres axons synapse? which neurotransmitter do they use?
inhibit the cells in the deep cerebellar nuclei
GABA
what do mossy fibres synapse with?
granule cells which then synapse with dendrites on purkinje cells
what do climbing fibres synapse with?
deep cerebellar nuclei and Purkinje cells.
what is the function of climbing fibres?
a central role in motor behaviors.
what do granule cells do?
send axons from granular layer to molecular layer where they split into 2 and head in opposite directions
what are parallel fibres?
the axons on neighbouring granule cells line up to form parallel lines
what is the structure of prukinje cells?
dendrites which form massive tree-like structures in the molecular layer. the dendritic trees span out perpendicularly to the parallel fibres and form numerous synapses with them.
how do climbing fibres interact with purkinje cells?
they tightly wrap around purkinje cells, forming hundreds of synapses with it
what are the 2 modes of firing by purkinje cells?
simple spikes- when they are stimulated by the parallel fibres of granule cells
complex spikes- when they are stimulated by climbing fibres so there is simultaneous activation of hundreds of synapses
what can damage to the cerebellum lead to?
1) loss of coordination of motor movement (asynergia)
2) the inability to judge distance and when to stop (dysmetria)
3) the inability to perform rapid alternating movements (adiadochokinesia)
4) movement tremors (intention tremor)
5) staggering, wide based walking (ataxic gait)
6) tendency toward falling
7) weak muscles (hypotonia)
8) slurred speech (ataxic dysarthria)
9) abnormal eye movements (nystagmus)
which side of the body would movement errors occur after damage to the cerebellum?
the same side- ipsilateral
what problems would arise after damage to the vestibulocerebellum?
Disturbances of balance and eye movements
what problems would arise after damage to the spinocerebellum?
Impaired gait, e.g. wide-based gait with small shuffling movements
what problems would arise after damage to the cerebrocerebellum?
Impairments in highly skilled sequences of learned movements
what problems would arise after damage to the superior cerebellar artery?
postural, upper limb and gait ataxia
what problems would arise after damage to the inferior cerebellar artery?
trunk ataxia
what is cerebellar ataxia?
Movements become jerky, imprecise and uncoordinated
what is dyssynergia?
loss of synergistic multi-joint movement
what is dysmetria?
Inability to judge distance
what is dysdiadochokinesia?
Inability to perform rapid, alternating movements
what are intention tremors?
Tremor when trying to move
what is ataxic dysarthria?
Slurred speech
what does cerebellar damage from alcohol look like?
Damage specifically affects movement of lower limbs (represented in anterior spinocerebellum) due to somatotropic arrangement
Wide and staggering gait but little impairment of arm or hand movements
what is the basal ganglia?
a group of subcortical nuclei including... caudate nuclei putamen globus pallidus substantia nigra sub-thalamic nucleus
what is the striatum?
the caudate nuclei and putamen
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what are the main input nuclei of the basal ganglia?
caudate nucleus and putamen (striatum)
what are the main output nuclei of the basal ganglia?
globus pallidus and substantia nigra (pars reticulata)
what are the functions of the basal ganglia?
control of movement
selection and maintenance of voluntary movements
inhibitory influence of motor systems
non-motor functions i.e. cognition, working memory etc
what is the primary input pathway for the basal ganglia?
Corticostriatal pathway
what is the nigrostriatal pathway?
inputs from the substantial nigra pars compacta enter the striatum via dopamine
what are the 2 main output pathways of the basal ganglia?
- striatum sends info to substantia nigra pars reticulata which sends outputs to the superior colliculus to control eye movements
- striatum sends info to the globus pallidus internal segment which projects up to the thalamus and then motor cortex to control limb and turn movements.
what is the function of the basal ganglia direct pathway?
accelerator to increase movement by removing tonic inhibition
what is the function of the basal ganglia indirect pathway?
brake. it decreases movement by increasing tonic inhibition
what is the effect of dopamine acting on D1?
it activates the direct pathway
what is the effect of dopamine acting on D2?
inhibits the indirect pathway
describe the direct pathway?
Command from cerebral cortex excites striatum, this inhibits globus pallidus (internal segment) to reduce the tonic inhibition of the thalamus. This allows the thalamus to excite motor cortex, initiating movement
how does the substantia nigra facilitate the direct pathway?
via D1 receptors in the striatum
describe the indirect pathway?
The cerebral cortex excites the striatum which inhibits the globus palidus (external segment) which in turn reduces the inhibition on the internal segment of the globus pallidus which increases the tonic inhibition of the thalamus. The external segement of the globus palidus also excites the subthalamic nucelus which increases tonic inhibition of the globus palidus internal segment. Overall, this reduces excitation of the motor cortex and inhibits movement.
how does the substantia nigra facilitate the indirect pathway?
via D2 receptors on the striatum
