The cerebellum and motor learning Flashcards
Role of the cerebellum
- Maintenance of balance and posture
- Coordination of voluntary movements
- Motor learning
- Cognitive functions
Principle of organisation of the cerebellum
- It compares movement intended to movement actually occurring
Cerebellar peduncles
- Superior cerebellar peduncle
- Middle cerebellar peduncle
- Inferior cerebellar peduncle
Functional subdivisions of the cerebellum
- Vestibulocerebellum
- Spinocerebellum
- Cerebrocerebellum
What separates the cerebellum into two
- Vermis
Location of the dentate nuclei
- Cerebellar hemispheres
Location of interposed nucleus
- Paravermal or intermediate zone
Location of fastigial nucleus
- Vermis
Role of fastigial nucleus
- Medial descending systems –> motor execution
Role of interposed nucleus
- Lateral descending systems –> motor execution
Role of dentate nucleus
- Areas 4 and 6 –> motor planning
Role of vestibular nucleus
- Balance and eye movements
Lobes of the cerebellum
- Anterior
- Posterior
- Flocculonodular
Effects of lesions to the cerebrocerebellum pathway
- Dysmetria, dysnergia, dysdiadochokinesia, intentional tremor and dysarthria
What is dysmetria
- movement is not stopped in time (overshoot)
What is dsynergia
- 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 the respiratory muscles, muscles of the larynx, etc uneven speech strength and velocity
What is limb ataxia
. Limb ataxia is present when a limb that has no deficits in strength wobbles during movement or misses its target
Steps of vestibular-ocular pathway reflex
1) Detection of rotation of fluid movement in canal
2) Excitation of extraocular muscles on one side
3) Inhibition of extraocular muscles on the other side
4) Compensating eye movement
Muscles used in the vestibular-ocular reflex
- Lateral rectus - Abducens nucleus(pons)
- Medial rectus - oculomotor nucleus(midbrain)
Effect of lesions to the vestibulocerebellar pathway
- Nystagmus
What is nystagmus
- Involuntary, rhythmical, repeated oscillations of one or both eyes, in any or all directions of view
- Movement of the eyes minimises the ability to focus the eyes on one point(fixation)
Effect of lesions in the spinocerebellar pathway
- Gait ataxia(unsteadiness of walking), and disturbance of limb tone(hypotonia) and posture
Cerebellar inputs
Mossy fibres and climbing fibres
Origin of mossy fibres
- From spinal cord and brainstem
Origin of climbing fibres
- From inferior olivary nucleus
Cerebellar outputs
- Deep cerebellar nuclei to
1) Thalami
2) Vestibular nuclei
3) Red nucleus
Layers of the cerebellar cortex(out to in)
- Molecular layer
- Purkinje cell layer
- Granule cell layer
- White matter
Where does the corticopontinecerebellar tract receive signals from
- Motor cortex
- Red nucleus
How does the cerebellum receive proprioceptive feedback
Via
- Spinocerebellum and vestibulocerebellum pathways
How is the actual response compared with desired response
- via the cerebrocerebellum inputs from the supplementary motor cortex and the primary motor cortex to produce error signals
What is the feedback loop
- Error signal is the difference between desired input and the output. The feedback comes from the output
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
What are error signals mainly derived from
- error signals derive mainly from sensory information e.g direction of ball whist playing tennis, error in playing a musical instrument will sound wrong
What are error signals sent via
- The inferior olivary nucleus which then lead onto the climbing fibres
What can alter the output of the purkinje cell
- 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.
Why is there a long-term reduction in activation of the purkinje cells to a given task
· 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.
Genetic causes of cerebellar dysfunction
· Inherited (rare) · Frederich’s ataxia · Spinocerebellar degeneration · (Ataxia may occur if major connections disrupted) · Ataxia-telengiectasia · Von Hippel Lindau
Haemangioblastomas(VHL)
Causes of acquired symmetrical ataxia
· Eg- · Alcohol · Metabolic (B12/Thyroid/Coeliac) · Drugs (eg phenytoin) · Degenerative (familial, MSA) · Immune (paraneoplastic)
Arteries supplying the cerebellum
Superior cerebellar artery (SCA)
Anterior inferior cerebellar artery (AICA)
Posterior inferior cerebellar artery (PICA)
Where are SCA and AICA branches of
- Basilar artery
What is PICA a branch of
- Vertebral artery
Venous drainage of the cerebellum
- Superior and inferior cerebellar veins
Where do the superior and inferior cerebellar veins drain into
- Superior petrosal sinus
- Transverse sinus
- Straight dural venous sinuses
Manifestations of cerebellar dysfunction
DANISH D - Dysdiadochokinesia (difficulty in carrying our rapid, alternating movements) A - Ataxia N - Nystagmus(coarse) I - Intention tremor S - Scanning speech H - Hypotonia
When is ataxia more profound in cerebellar dysfunction
- Often more profound if cerebellar nuclei, brainstem nuclei or white matter tracts involved(MS) than cerebellar cortex as some degree of plasticity
Path of climbing fibres
- neuronal projections from the inferior olivary nucleus located in the medulla oblongata
- Axons pass through the pons and enter the cerebellum via the inferior cerebellar peduncle where they form synapses with the deep cerebellar nuclei and Purkinje cells.
- Each climbing fiber will form synapses with 1–10 Purkinje cells.
