Cerebellum and motor learning Flashcards
Cerebellum function [4]
Maintains balance and posture
Co-ordinates voluntary movements
- Compares movement intended to movement actually occuring
Motor learning
Cognition
Cerebellar peduncles
Connects the cerebellum to the midbrain.
Three sections:
- Superior: output to the cerebral cortex via thalamic nuclei
- Middle: Connects to the pons via pontine nuclei
- Inferior: Spinocerebellar tract and inferior olive fibres
Lobes of the cerebellum
- Anterior
- Posterior
- Flocculonodular
Vestibulocerebellum
Functional division of the cerebellum
- Located in the flocculonodular lobe
Function:
- Contains vestibular nuclei involved in balance and eye movements
Vestibulocerebellum pathways
Inputs:
- Receives from the semicircular canals of the ear
- Receives afferent fibres from the vestibular nuclei.
Outputs:
- Sends fibres to the vestibular nuclei
- Medial vestibular nuclei leads to vestibulospinal tract
- Lateral vestibular nuclei branches synapse at extra-occular muscle nuclei
Spinocerebellum
- Structure
- Function
Composed of the vermis and paravermis- contains two somatotopic maps of the body
- Vermis: Fastigial nucleus—-> medial descending systems
- Paravermis: interposed nucleus—> lateral descending systems
Function:
- Motor execution: controls muscle tone and posture
Spinocerebellum paths
Inputs:
- Spinocerebellar tracts
Outputs:
- Reticulospinal tract
- Vestibulospinal tract
Cerebrocerebellum
- Structure
- Function
Composed of the lateral aspect of the cerebral hemispheres.
- Contains dentate nucleus
Function:
- Dentate nucleus communicates with cortical areas 4+6= motor planning
Cerebrocerebellum paths
Input
- Corticopontine tract [primary motor cortex to pontine nuclei]
- Pontocerebellar tract [pontine nuclei to cerebellar cortex]
Output
- Cortex to dentate nuclei
- Dentate nuclei to thalamic nuclei
- Thalamus to primary motor cortex
Lobar anatomy of cerebellum
Vermis
- Contains fastigial nucleus
Paravermis
- Contains interposed nucleus
Hemisphere
- Contains dentate nucleus
Superior cerebellar peduncle pathways
Exit for outputs to:
- Thalamus [ from dentate nucelus]
- Red nucleus [interposed nucleus]
- Vestibular nuclei [fastigial nucleus]
Middle cerebellar peduncle pathways
Contains input from the pontocerebellar tract [from corticopontine tract]
Inferior cerebellar peduncle pathways
Allows entry of outputs from:
- Inferior olive tract
- Spinocerebellar tract
Dysmetria
Type of ataxia
- Lack of co-ordination
- Overshoot or undershoot for the intended position of: hand, arm, leg, eye.
- Movement is not stopped in time
Dsynergia
The inability to conduct complex movements
- Movements are uncoordinated and abrupt
Dysdiadochokinesia
- Defintion
- Location of lesion
Type of ataxia
Reduced ability to conduct rapidly alternating movements
- Lesion in cerebellar hemisphere or frontal lobe
Intentional tremor
Tremor that arises when trying to perform a visually guided or deliberate movement.
Caused by lesion in vestibular nuclei [i.e in the superior cerebellar peduncle]
Dysarthria
Incoordination of the respiratory muscles
- Of the larynx, etc
Causes unclear articulation of speech
Vestibular-ocular pathway
Pathway from the vestibular apparatus in the ear to the extra-ocular muscles
- Vestible—> CN VIII–>vestibular nucleus in the pons
- Fibres from the vestibular nucleus crosses —-> enters abducens nucleus
- Abducens nerve from the nuclei—> lateral rectus
- Fibres from abducens nuclei—> occulomotor nuclei—-> medial rectus
Nystagmus
- Definiton
- Pathway lesion
Involuntary, rhythmic, oscillations of one or both eyes
- In all directions of views
Prevents eye fixation
Can be caused by lesion of the vestibulocerebellar pathway
Spinocerebellar tract lesion effects
Gait ataxia
- Unsteady walking
Hypotonia of the limbs and posture
Cerebellar inputs and outputs
Inputs:
- Mossy fibres: from brainstem [pontine, middle cerebellar peduncle] and spinal cord [spinocerebellar tract, inferior cerebellar peduncle]
- Climbing fibres: from inferior olivary nucleus in brainstem.
Outputs, from deep cerebellar nuclei, via superior cerebellar peduncle:
- Thalami
- Vestibular nuclei
- Red nucleus
Cerebellar cortex layers
Molecular layer
Purkinje cell layer
- Contains many parallel fibres to each cell
Granule cell layer
- Contains granule cells and golgi cell
White matter layer
- Contains moss fibres and climbing fibres
- Climbing fibre to one purkinje cell but contains many synapses
Inputs and outputs of the Purkinje cells
Inputs
- Convergence from parallel fibres [from granule cell] to purkinje dendrites
- One climbing fibre to a purkinje cell that diverges
Output
- To deep cerebellar nuclei
Feedback loop - motor learning
- Desired output
- Erro signal—-> effector muscle—> output
Feedback signal comes from the output—> leads to correction
Feedforward loop
Movements too fast to be corrected by feedback
- Done via predictions of pervious outcomes
Advanced information generates desired output —> fed foward to generate an output
Error signals
Derives from sensory information
- Sent via infeiror olivary nucelus —> climbing fibres
Genetic cause of cerebellar dysfunction
Frederich’s ataxia
Spinocerebellar degeneration
Ataxia-telengiectasia
Von Hippel Lindau
Acquired symmetrical ataxia causes
Alcohol
Metabolic [Low B12, thyroid, ceoliac disease]
Drugs [like phenytoin]
Degenerative disease
Immune
Cerebellar motor loop
- Axons from: Area 4 +6
- Somatosensory cortex
- Posterior parietal cortex
- –> Converge into the pontine nuclei - Projections of the pontine nuclei enters the cerebellum
- Projections from cerebellum—> ventral lateral nucleus in thalamus
