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Cell Bio 10- Cerebellum
Cerebellum has no direct connections to lower motor neurons
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Cerebellar lesions result in a characteristic type of irregular uncoordinated movement, ataxia
Lesions can be localized easily:
1. Ataxia is ipsilateral to the side of a cerebellar lesion
2. Midline lesions of the cerebellar vermis or flocculonodular lobes mainly cause unsteady gait (truncal
ataxia) and eye movement abnormalities
3. Lesions lateral to the cerebellar vermis mainly cause ataxia of the limbs (appendicular ataxia)
Deep Cerebellar Nuclei
Dentate nuclei: receive projections from the lateral cerebellar hemispheres (active just before voluntary movements)
Emboliform & globose nuclei: receive inputs from the intermediate part (active during and in relation to the movement)
Fastigial nuclei: receive inputs from the vermis
Cell Bio 10- Cerebellum
Cerebellar Input and Output pathways
INPUT-1: Mossy fibers, ascend through the cerebellar white matter and form excitatory synapses on granule cells
Granule cells’ axons form parallel fibers, each of these fibers form excitatory synapses with numerous Purkinje Cells.
 All output from the cerebellar cortex is carried by the axons of Purkinje cells
Purkinje cells form inhibitory synapses onto deep cerebellar nuclei and vestibular nuclei
INPUT-2: Climbing fibers arise from neurons in the contralateral inferior olivary nucleus. They wrap around the cell body
and proximal dendritic tree of Purkinje cells, forming powerful excitatory synapses
A single climbing fiber will branch to supply about 10 Purkinje cells; however each Purkinje cell is excited by just
one climbing fiber
Cell Layers of Cerebellar Cortex
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Mossy fibers excite granule cells, which excite the inhibitory Purkinje cells.
Climbing fibers excite Purkinje cells directly
Purkinje cells have fanlike dendritic trees, parallel fibers pass through these, then basket cell axons pass
perpendicular to the parallel fibers
All axons projecting upward are excitatory
All axons projecting downward are inhibitory
The outputs of the deep cerebellar nuclei are excitatory
Cell Bio 10- Cerebellum
Outputs from the lateral cerebellar hemisphere (below) via the dentate nucleus (involved in motor planning)
Output from the intermediate cerebellar hemisphere (above) (involved in the control of ongoing movements of distal
extrem.
Output from the cerebellar vermis and flocculunodular lobe (below) (vermis: proximal trunk movement;
flocculonodular: vestibule-ocular control)
Cell Bio 10- Cerebellum
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Somatotopic Organization of Multimodal Inputs to the Cerebellum
Noradrenergic inputs from the locus coeruleus and serotonergic inputs from the raphe nuclei project diffusely
throughout the cerebellar cortex
o These inputs play a neuromodulatory role
Finger-Nose-Finger Test
In ataxia, the movements have an irregular, wavering course that seems to consist of continuous overshooting,
overcorrecting, and then overshooting again around the intended trajectory
Appendicular ataxia: Coordinated actions of agonist and antagonist muscles acting on multiple joints, including
the shoulder, elbow, and wrist, are required to smoothly perform this movement in a normal fashion
Truncal Ataxia: Lesions confined to the cerebellar vermis affect primarily the medial motor systems. Patients
with such lesions therefore often have a wide-based, unsteady “drunklike” gait
Appendicular ataxia: Lesions of the intermediate and lateral portions of the cerebellar hemisphere affect the
lateral motor systems. Therefore, these patients have ataxia on movement of the extremities