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CEREBELLUM
INTRO
Crucial for coordination, accuracy, efficiency of movement
No direct access to motorneurons or to spinal cord
Indirect role
Gather and integrate signals from
- relevant sensory modalities
- pre-motor interneuron pools
Modulate other descending pathways
Air traffic control analogy (can fly without it, but uncoordinated, unsafe)
Cerebellar lesions produce:
No paralysis
No sensory loss
Ataxia (incoordination)
GROSS STRUCTURE
Surface features
Hemisphere
Vermis
Flocculo-nodular lobe
Folia
Peduncles
One per brainstem division (lesions in each division can produce ataxia
by affecting these fibers)
Input vs. output fibers (by peduncle)
Middle mainly input; superior mainly output; inferior both
Internal anatomy
Cortex
White matter
Deep nuclei
Dentate
Interpositus (= globus + emboliform)
Fastigial
MICROSCOPIC ANATOMY
Layers of cortex
Molecular layer
Granule-cell layer
Purkinje cell layer
Purkinje cells as sole cortical output
Input fibers
Mossy fibers
 granule cell
 parallel fibers (granule cell axons)
Climbing fibers
 direct contacts onto Purkinje cells
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Interneurons
Several (basket, stellate, Golgi)
Basket-cell example
Lies in molecular layer
Parallel fiber inputs
Inhibit Purkinje soma and hillock
Lateral inhibition (flanks a "beam" of Purkinje cells excited by their
parallel fibers)
Purkinje cells are inhibitory
Sculpting of high resting activity of deep nuclei
INPUT PATHWAYS
Logic - what need for coordination
Muscle / joint (from SPINAL CORD)
Cutaneous (from CORD)
Interneuron pool status (from CORD)
Orientation with respect to gravity; movement (VESTIBULAR)
Ongoing motor plans with respect to complex extrapersonal space (from
NEOCORTEX)
These classes of information target different cerebellar regions
Vestibulo-cerebellum (flocculo-nodular lobe and vermis)
Spino-cerebellum (vermis and para-vermal hemisphere)
Cerebro-cerebellum (cerebellar hemisphere)
Spinal inputs
SPINOCEREBELLUM
Vermis
Paravermal
Topography (axial structures represented at midline vermis)
IPSILATERAL relationship of cerebellum to spinal cord and body
DORSAL SPINOCEREBELLAR TRACT
Afferents: Class I and II; muscle, joint, cutaneous
Dorsal columns
Clarke's column (thoracic)
Lateral funiculus (relatively dorsal there, hence the tract's name)
Inferior cerebellar peduncle
Spinocerebellum
CUNEO-CEREBELLAR TRACT
Upper-limb equivalent of dorsal spinocerebellar tract
Afferents same
Relay: external cuneate nucleus (medulla)
VENTRAL SPINOCEREBELLAR TRACT
Origin: interneuron pools
Does carry some crude sensory information
But mainly "premotor" signals (status of interneurons)
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Decussation
Lateral funiculus
Relatively ventral there, hence tract name
Superior peduncle
Cerebellum
Crossed pathway? Doesn't fit rule, but
- some recross
- axial representation which typically gets bilateral input
ROSTRAL SPINOCEREBELLAR TRACT
Upper-limb equivalent of ventral spinocerebellar
Vestibular inputs to cerebellum
Secondary sensory mainly
Some primary (from Scarpa's ganglion)
Cerebellar targets
Vestibulocerebellum
Vermis
Cerebral Cortical inputs to cerebellum
Pathway indirect via pontine nuclei
Cerebellar targets
Hemisphere (cerebro-cerebellum)
Paravermis (convergence with spinal input)
Major component of cortico-brainstem fibers
Of fibers in cerebral peduncle
- fully 50% participate in corticopontine pathway
- only 5% contribute to corticospinals
Explains why medullary pyramid so much smaller than cerebral
peduncle
Decussation of ponto-cerebellar fibers
Preserves cortical and cerebellar lateralities
Transverse fibers visible in sections
Inferior olive
All above systems terminate as mossy fibers
Olive as sole climbing-fiber source
Inputs to olive
Spinal
Brainstem (midbrain)
Cerebral cortex
Olivo-cerebellar fibers are crossed (decussating)
Reticular formation
Diverse functions
Partly, feedback from origin of one descending path used by cerebellum
Other output relays also feed back (e.g., vestibular nuclei; cerebral
cortex; red nuclei).
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FUNCTIONAL ZONES OF CEREBELLUM (refer to table)
Inputs distinguish (see above)
Outputs to deep nuclei differ, which in turn relate them to different…
- muscle groups (preferential targeting of axial; proximal limb/girdle; or
distal muscle groups)
- functional association (balance/posture; gait; fine manipulation)
- descending pathways
REGION
ZONE
DIVISION
Flocculonodular
Vermis
Flocculonodular
Median
Vestibulocerebellum
Paravermal
Paramedian or
Intermediate
Hemisphere
Lateral
Spinocerebellum
Cerebrocerebellum
DEEP
NUCLEUS
Vestibular
nuclei
Fastigial
Interpositus
Dentate
INPUTS
MUSCLES
FUNCTION
Vestibular
(1º and 2º)
Spinal (trunk) and
vestibular
Spinal (limb) &
corticopontine
Axial
Equilibrium
Posture
Equilibrium Posture
Corticopontine
All, especially
distal limb
Axial
Limb
Posture
Gait
Global, especially fine
movement, planning
CEREBELLUM
Cerebral
Cortex
Lateral
Paramedian
Median
Flocculo-nodular
Dentate
Interpositus
Fastigial
Vestibular nuclei
Thalamus
(VL)
Red
Nucleus
Reticular
Formation
Spinal
Cord
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