Circuitry

The basic cerebellar circuits begin with Purkinje cells that receive excitatory input direcdy from ■ climbing fibers and from parallel fibers of granule cells.

i Purkinje cell axons project to and inhibit the deep cerebellar nuclei or the vestibular nuclei in an orderly fashion (Figure IV-6-3).

• Purkinje cells in the flocculonodular lobe project to the lateral vestibular nucleus.

• Purkinje cells in the vermis project to the fastigial nuclei.

• Purkinje cells in the intermediate hemisphere primarily project to the interposed (globose and embofiform) nuclei.

• Purkinje cells in the lateral cerebellar hemisphere project to the dentate nucleus.

Red nucleus (midbrain)

F recentral gyrus

Deep Cb ! .nuclei (Ty Fastigialj nucleus Interpositus \

nucleus ^^ 0 Dentate nucleus v^y

Purkinje cell axons

Vermis

Lateral hemisphere Paravermal hemisphere ^

\ f~~' t j Rubrospinal V tract Corticospinal tract

Figure IV-6-3. Cerebellar Efferents

Table IV-6-4. Major Efferents From the Cerebellum

Cerebellar Areas

Deep Cerebellar Nucleus

Efferents to:

Function

Vestibulocerebellum (F1 occulo n o dul ar lobe)

Fastigial nucleus

Vestibular nucleus

Elicit positional changes of eyes and trunk in response to movement of the head

Spinocerebellum

(Intermediate hemisphere)

Interpositus nucleus

Red nucleus

Reticular formation

Influence LMNs via the reticulospinal and rubrospinal tracts to adjust posture and effect movement :

Pontocerebellum (Lateral hemispheres)

Dentate nucleus

Thalamus, then Cortex

Influence on LMNs via the corticospinal tract, which effect voluntary movements, especially sequence and precision

Clinical Correlate

Anterior vermis lesions are usually the result of degeneration from alcohol abuse and are present with gait ataxia, Posterior vermis lesions result from medulloblastomas or ependymomas and present with truncal ataxia.

Efferents from the deep cerebellar nuclei leave mainly through the SCP and influence ail upper motoneurons. In particular, axons from the dentate and interposed nuclei leave through the SCP, cross the midline, and terminate in the ventrolateral (VL) nucleus of the thalamus.

The VX- nucleus of the thalamus projects to primary motor cortex and influences the firing of corticospinal and corticobulbar neurons.

Axons from other deep cerebellar nuclei influence upper motoneurons in the red nucleus and in the reticular formation and vestibular nuclei.

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