Functional Organization of the Cerebellum

The cerebellum is an important member of the central motor control system. As with the basal ganglia, the cerebellum forms part of extensive motor loops concerned with the initiation and coordination of movement. The cerebellum appears to be an integrating center for afferent sensory and other inputs. There are about 40 times the numbers of afferent inputs than there are efferent outputs from the cerebellum. The cerebellum receives afferents from ascending spinal tracts, the cerebral cortex, the eye, and from the vestibular apparatus.

Functionally, the cerebellum can usefully be considered as three separate compartments or modules, each consisting of an area of cerebellar cortex together with its associated deep-lying white matter and nuclei. These are the vestibulocerebel-lum, spinocerebellum and the pon-tocerebellum. The vestibulocerebellum consists of the flocculonodular node together with the adjacent areas of the ver-mis (vermian lobule 9).

The vestibulocerebellar cortex receives afferents from the vestibular nucleus and the ipsilateral vestibular ganglion. This module is called the archicere-bellum (see also p. 18), since it is phylo-genetically the oldest part of the cerebellum. The vestibulocerebellar outflow is concerned chiefly with the orientation of the head and body in space, and with certain eye movements.

The spinocerebellar module consists of the intermediate and adjacent vermian zone. The module receives its inputs from ascending spinocerebellar and cuneo-cerebellar tracts. Fibers that enter the ver-mian zone project collaterals to the fastigial nucleus. Those that enter the intermediate zone send collaterals to the globose and emboliform nuclei. The spinocerebellar outputs are concerned with the control of axial and limb musculature.

The pontocerebellar module (also called the cerebrocerebellar or neocere-bellar module) is the largest zone, and consists of the lateral area. This module receives most of its inputs as crossed afferents from the basal pontine nuclei through the middle cerebellar peduncle. A major pathway exists from the cerebral cortex to the ipsilateral pontine nucleus and incoming afferents project collaterals to the dentate nucleus. Another important afferent pathway is the olivocerebellar pathway from the principal inferior olivary nucleus. The pontocerebellum, which is phylogenetically the newest module, is important in the planning and timing of movements of the hand and forearm. It sends corticonuclear projections to the dentate nucleus, which in turn projects to the cerebral cortex. The dentate nucleus, also, is the source of cerebellar efferent fibers to the cerebral cortex.

The inputs to the cerebellum are topographically organized; the same area of the body may be represented in more than one area of the cerebellum. This has been called fractured somatotopy. This phenomenon may be due, at least in part, to the fact that the cerebellum receives inputs from several different sources. Sensory information may be fed directly to the cortex, or may arrive after being processed in, for example, the cerebral cortex, and be sent to another cerebellar cortical area.

Spinocerebellum Somatotopy

intermediate zone spinocerebellum primary fissure pontocerebellum (lateral zone) vestibulocerebellum cerebellar functional subdivisions intermediate zone spinocerebellum primary fissure pontocerebellum (lateral zone) vestibulocerebellum spinocerebellar-pontocerebellar overlap

Cerebellar Somatotopy

paramedian lobe flocculus paramedian lobe flocculus somatotopic organization in primate cerebellar cortex

tract

origin

via peduncle

cuneocerebellar

lateral cuneate nucleus

inferior

corticocopontocerebellar

pontine nuclei

middle

dorsal spinocerebellar

spinal cord

inferior

reticulocerebellar

reticular formation

inferior

olivocerebellar

accessory and inferior olive

inferior

ventral spinocerebellar

spinal cord

superior

trigeminocerebellar

trigeminal nerve

inferior

tectocerebellar

inferior and superior colliculi

superior

some principal inputs to the cerebellum

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  • gildo fiorentino
    How is the cerebral cortex organized?
    7 years ago

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