The Cerebellum and Motor Learning Flashcards
Cerebellum: Function:
- receives sensory info
- influences motor function
- involved in motor learning and higher
function - not involved in interpretation or
discrimination - does not initiate movement
Cerebellar Anatomy:
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Label the diagram below.
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Three lobes of the cerebellum are
- anterior
- posterior
- flocculonodular
The two hemispheres of the cerebellum are connected in the midline by the
vermis
Functional organisation of the cerebellum:
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Internal structure of the Cerebellum:
- outer layer is the cerebellar cortex
- white matter tracts
- deep cerebellar nuclei:
- fastigial nucleus medially
- dentate nucleus laterally
- interposed nucleus in between the
globose and emboliform nucli
Cerebellar Afferents travel
- directly from the spinal cord
- via the brainstem nuclei
All input into the cerebellum is
excitatory
Afferent pathway to the cerebellum:
- sensory information from muscle
spindles or golgi tendon organs in
skeletal muscle travels to the cerebellum
through - direct ipsilateral pathways (dorsal
spinocerebellar, cuneocerebellar and
ventral spinocerebellar - synapses with brainstem nuclei (inferior
olivary nuclei) and passes over to the
contralateral cerebellar cortex cia the
inferior peduncle
Three direct ipsilateral pathways for sensory information from the muscle cells to cerebellum:
- dorsal spinocerebellar tract: info on
individual muscles of legs - cuneocerebellar tract: info on individual
muscles of arms - ventral spinocerebellar tracts: whole
limb, synergy of movement
Vestibular nuclei relays info from
the vestibular system to the cerebellum
Reticular Formation Nucleus: Function:
modulating spinal reflexes acting on extensors
Red Nucleus: Function:
relays info from cerebral cortex to cerebellum via the inferior olivary nucleus
Inferior Olivary Nucleus: Function:
integrates signals from spinal cord and the cerebral cortex
Deep Pontine Nuclei: Function:
fibers from all regions of the cerebral cortex synapse with deep pontine nuclei to connect to the contralateral cerebellum via transverse fibers
Tectum Nuclei: Function:
fibers from inferior and superior colliculus provide auditory and visual input to the cerebellum via deep pontine nuclei
Cerebellar Output
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Functional part: Vestibulocerebellum:
- involved in balance/eye movement
- input from vestibular nuclei to the
folocculonodular lobe - output via vestibular nuclei and co-
ordinates with visual cortex, superior
colliculus and reticular formation nuclei
Vestibulocerebellum:
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Functional Part: Spinocerebellum:
- vermal and paravermal cortex
- inputs from spinocerebellar tracts and
brainstem nuclei - vermis: output via fastigial nucleus and
medial descending tracts affecting
motor execution - paravermis:
- output via interposed nuclei and
lateral descending tracts affecting
motor execution
- output via inferior olivary nucleus to
red nucleus and cerebral cortex for
motor control and learning
Spinocerebellum:
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Functional Part: Pontocerebellum/Cererbrocerebellum:
- remaining lateral part, largest volume
- main input via deep pontine nuclei,
giving rise to transverse pontin fibers
that enter cerebellum by contralateral
middle cerebellar pepduncle - output via dentate nucleus
- role in motor planning, control etc
- role in cognition, speech, behaviour
All output from the cerebellum to the deep cerebellar nuclei is ———-
inhibitory
All output from the deep cerebellar nuclei is
excitatory
All messages from the cerebellum are coded by
excitation and inhibition
What are the two main types of fibers that input into the cerebellum?
- mossy fibers
- climbing fibers
Cerebellar Cortex: 3 Layers:
- molecular layer
- purkinje cell layer: output from the
cerebellar cortex to deep nuclei
(inhibitory) - granule cell layer (outermost layer)
Output from the cerebellum occurs via the (2):
deep cerebellar nuclei or vestibular nuclei
Somatotopic Representation of the cerebellum:
area on the body that corresponds to a particular part of the nervous system
Cerebellum: Granular Layer: Cell Types:
- mainly granule cells (dendrites receive
mossy fiber afferents) - golgi cell dendrites contact terminals of
mossy fibers and dendrites of granule
cells in cerebellar glomerulus
Granular Layer:
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Granule Cells:
- in granule layer
- 3-5 dendrites from granule cell receive
mossy fiber afferents - axon ascends to cortex surface
- bifurcates in molecular layer
- parallel fibers contact the purkinje cell
dendrites and excite the purkinje cells
Golgi cells:
- granular layer
- inhibitory GABA-ergic
- receives afferents from parallel fibers
and from mossy fibers - contacts dendrites of granule cells and
terminals of mossy fibers
Cerebellar: Purkinje Cell Layer:
- contains purkinje cell
- one cell layer thick
- thick dendrites project to the molecular
layer - axon descends to deep cerebellar nuclei
or vestibular nuclei - output is inhibitory
Cerebellar Cortex: Molecular Layer:
- dendrites of purkinje cells
- terminal branches of climbing fibers
- parallel fibers of granule cells
- 2 types of interneurons: basket cells and
stellate cells, which make inhibitory
contact with purkinje cells to sharpen
the focus
Climbing Fibers:
- from inferior olivary nucleus
- branches may synapse with deep
cerebellar nucleus (stimulatory) - ascends to molecular layer of cerebellar
cortex - synapses with dendrites of one purkinje
cell - one climbing fiber to one purkinje cell,
purkinje cell output is inhibitory
Mossy Fibers:
- branches in granular layer can directly
stimulate deep cerebellar nucleus - end in mossy fiber rosettes, held by
dendrites of granule cells - granule cells then influence purkinje
cells through parallel fibers - also contact golgi cell dendrites
Action of mossy fibers and climbing fibers on purkinje cells lead to
motor learning
Synaptic plasticity of purkinje cells in cerebellum initiated by
the repetition of an action
Symptoms affecting movement and tone are less likely to cause symptoms if dysfunction is in
the cerebellar cortex
Cerebellar dysfunction symptoms are worse if what structure if affected?
the cerebellar nuclei
If the paravermal cerebellar hemisphere is affected what symptoms would be seen?
affects ipsilateral function (connections via interposed nuclei or dentate nuclei)
If the cerebellar vermis is affected what symptoms would be seen?
affects trunk, axxial muscles and eye movements
Cerebellar Dysfunction: Symptoms:
- uncoordinated movements
- tremor
- unsteadiness
- oscillopsia
- slurring of speech
Cerebellar Dysfunction: Signs:
- finger nose incoordination
- dysdiadokokinesia
- heel shin incoordination
- gait ataxia
- hypotonia
- nystagmus
- staccato speech
A space occupying lesion or vascular lesion in one hemisphere of the cerebellar dysfunction.
Symptoms and signs?
- ipsilateral past pointing, dysdiadokinesia
- intention tremor
- lateral hemisphere projects via dentate
nucleus to cerebral cortex via thalamus - feedback to motor cortex disrupted
- affects intentional movements
Alcoholic Cerebellar Degeneration:
- affects
- symptoms
- signs
- affects midline anterior vermis and
paravermis - legs>arms incoordination
- truncal ataxia most marked
- nutritional deficiency leads to
degeneration of purkinje cells more
marked in regions discussed - axial muscles represented more
medially, close to vermis - legs represented in the anterior
paravermal region
Medulloblastoma affecting the fastigial nucleus and vermis symptoms and signs?
- truncal ataxia due to midline vermis
involvement - nystagmus as connections via fastigial
and vestibular nuclei
