The cerebellum and motor learning Flashcards
What is the role of the cerebellum?
Maintenance of balance and posture
Coordination of voluntary movements
Motor learning
Cognitive functions
Which level of the motor control hierarchy is the cerebellum involved in?
Middle level
Tactics
Along with the motor cortex
What is another name to describe the cerebellum?
The great comparator
Describe what the cerebellum does to perform its function
Compares what you intend to happen to what is actually happening
Sends out a correction signal involving planning, initiation and execution for an event you intend on occuring.
Describe the location of the cerebellum
Posterior to 4th ventricle
Posterior to brainstem
Inferior to occipital lobe
Describe the structure of the cerebellum
3 lobes - anterior, posterior, flocculonodular
Arbor vitae
Cerebellar nucleus
Lobes separated by vermis
List the functional subdivisions of the cerebellum
Vestibulocerebellum
Spinocerebellum
Cerebrocerebellum
How many somatotopic maps of the body are found in the spinocerebellum?
2
Which nuclei are found in the lobes of the cerebellum?
Fastigial
Interposed
Dentate
Describe the cerebellar outputs of the fastigial nucleus
Medial descending systems - motor execution
Describe the cerebellar outputs of the interposed nucleus
Lateral descending systems - motor execution
Describe the cerebellar outputs of the dentate nucleus
areas 4 and 6 - motor planning
Describe the cerebellar outputs of the vestibular nucleus
balance and eye movements
What is the importance of the spinocerebellum?
Control of posture and muscle tone
Give some examples of effects of lesions to cerebrocerebellum pathway
Dysmetria Dysnergia Dysdiadochokinesia Intentional tremor Dysarthria
What is dysmetria?
Movement is not stopped in time
What is dysnergia?
Decomposition of complex movements
What is dysdiadochokinesia?
Reduced ability to perform rapidly alternating movements
What is an intentional tremor?
Tremor arising when trying to perform a goal directed movement
What is dysarthria?
Articulation incoordination
Incoordination in respiratory muscles, muscles of the layrnx etc.
Uneven speech strength and velocity
Give the effect to lesions in the vestibulocerebellar pathway
Nystagmus - involuntary, rhythmic, repeated oscillations of one or both eyes in any or all directions of view.
Movement of the eyes maximises the ability to focus the eyes on one point (fixation)
Give an effect of a lesion to the spinocerebellar pathway
Gait ataxia (unsteadiness when walking) and disturbance of limb tone (hypotonia) and posture
Describe cerebellar inputs and outputs
Inputs:
- Mossy fibres from spinal cord and brainstem
- Climbing fibres from inferior olivary nucleus
Outputs:
- Deep cerebellar nuclei to thalami, vestibular nuclei and red nucleus
What is the output of purkinje cells?
Deep cerebellar nuclei
How many climbing fibres are there per purkinje cell?
1 but many synapses (divergence)
Describe the relationship between parallel fibres and purkinje cells
1 Parallel fibre per purkinje cell but one or few synapses on each (convergence)
List the layers of neuron classes
Molecular layer
Purkinje cell layer
Granule cell layer
Describe feedback during motor learning
Motor cortex and red nucleus generate signals via the corticopontinecerebellar tract.
Proprioceptive feedback from muscles and joints via the spinocerebellum and the vestibulocerebellum pathways.
Actual response is compared with desired response via the cerebrocerebellum inputs from the supplementary motor cortex and the primary motor cortex to produce error signals.
Describe a feedback loop
Error signal is the difference between desired input and the output. The feedback comes from the output.
Describe the feedforward loop
Movements that are too fast to be corrected by feedback are executed using predictions of their outcome based on experiences. Crucial for learning new motor skills e.g riding a bicycle, playing tennis, driving.
Advanced informaiton is used to generate the desired output and this fedforward to generate the output. Waiting for a feedback from the output would be too low.
The error signals derive mainly from sensory information e.g direction of ball whist playing tennis, error in playing a musical instrument will sound wrong. The error signals are sent via the inferior olivary nucleus which then lead onto the climbing fibres
Describe the complex spikes of the cerebellum
The combination of the climbing fibres (error signal/complex spikes, background firing rate is 20-50Hz) and the mossy fibres (desired signal/simple spikes, Background firing rate 50-100Hz) will alter the output of the purkinje cell till you get a desired response.
As a task is being learned, there are lots of complex and simple spikes. As complex spikes decrease, it changes the connections between the parallel fibres and the purkinje cells resulting in a reduction in effect from the simple spikes. The long-term reduction in activation of the purkinje cells to a given task is an example of plasticity.
List some genetic causes of cerebellar dysfunction
Inherited (rare)
Frederich’s ataxia
Spinocerebellar degeneration
(Ataxia may occur if major connections disrupted)
Ataxia-telengiectasia
Von Hippel Lindau
Give some causes of acquired symmetrical ataxia
Alcohol Metabolic (B12/Thyroid/Coeliac) Drugs (eg phenytoin) Degenerative (familial, MSA) Immune (paraneoplastic)
Describe the vascular anatomy of the cerebellum
Branches of basilar artery: Vertebral SCA AICA PICA
When is ataxia more profound?
if cerebellar nuclei,
brainstem nuclei or white matter tracts involved (MS)
than cerebellar cortex as some degree of plasticity
