Cerebellar afferents

Information relevant to the role of the cerebellum in motor regulation comes from the cerebral cortex, the brainstem, and from the muscle receptors in the periphery. The information is conveyed to the cerebellum mainly via the middle and inferior cerebellar peduncles.

• Inferior Cerebellar Peduncle: The inferior cerebellar peduncle goes from the medulla to the cerebellum. It lies behind the inferior olivary nucleus and can sometimes be seen on the ventral view of the brainstem (as in Figure 7). This peduncle conveys a number of fiber systems to the cerebellum. These are shown schematically in this diagram of the ventral view of the brainstem and cerebellum. They include the following:

• The posterior (dorsal) spino-cerebellar pathway conveys proprioceptive information from most of the body. This is one of the major tracts of the inferior peduncle. These fibers, carrying information from the muscle spindles, relay in the dorsal nucleus of Clarke in the spinal cord (see Figure 32). They ascend ipsilaterally in a tract that is found at the edge of the spinal cord (see Figure 68). The dorsal spino-cerebellar fibers terminate ipsilaterally; these fibers are distributed to the spino-cerebellar areas of the cerebellum.

• The homologous tract for the upper limb is the cuneo-cerebellar tract. These fibers relay in the accessory (external) cuneate nucleus, located in the lower medulla (see Figure 67B and Figure 67C). This pathway is not shown in the diagram.

• The olivo-cerebellar tract is also carried in this peduncle. The fibers originate from the inferior olivary nucleus (see Figure 6, Figure 7, Figure 67, and Figure 67B), cross in the medulla, and are distributed to all parts of the cerebellum. These axons have been shown to be the climbing fibers to the main dendritic branches of the Purkinje neurons. • Other cerebellar afferents from other nuclei of the brainstem, including the reticular formation, are conveyed to the cerebellum via this peduncle. Most important are those from the medial (and inferior) vestibular nuclei to the vestibulocerebellum. Afferents from the visual and auditory system are also known to be conveyed to the cerebellum.

• Middle Cerebellar Peduncle: All parts of the cerebral cortex contribute to the massive cor-tico-pontine system of fibers (also described with Figure 48). These fibers descend via the anterior and posterior limbs of the internal capsule, then the inner and outer parts of the cerebral peduncle, and terminate in the pontine nuclei. The fibers synapse and cross, and go to all parts of the cerebellum via the middle cer-ebellar peduncle (see Figure 6 and Figure 7). This input provides the cerebellum with the cortical information relevant to motor commands and the planned (intended) motor activities.

• Superior Cerebellar Peduncle: Only one afferent tract enters via the superior cerebellar peduncle (see below). This peduncle carries the major efferent pathway from the cerebellum (discussed with Figure 57).

Additional Detail

One group of cerebellar afferents, those carried in the ventral (anterior) spino-cerebellar tract, enters the cerebellum via the superior cerebellar peduncle. These fibers cross in the spinal cord, ascend (see Figure 68), enter the cerebellum, and cross again, thus terminating on the same side from which they originated.

Fronto-pontine fibers

Temporo-pontine fibers Parieto-pontine fibers Occipito-pontine fibers

Inferior cerebellar peduncle Medial vestibular nucleus

Dorsal spino-cerebellar tract Dorsal nucleus of clarke —

Cortico-bulbar (and Cortico-spinal) fibers

Fronto-pontine fibers

Cortico-bulbar (and Cortico-spinal) fibers

Temporo-pontine fibers Parieto-pontine fibers Occipito-pontine fibers

Vestibulo Cerebellum

Ponto-cerebellar fibers

Middle cerebellar peduncle

Inferior cerebellar peduncle Medial vestibular nucleus

Dorsal spino-cerebellar tract Dorsal nucleus of clarke —

Inferior olivary nucleus

Olivo-cerebellar fibers

Ponto-cerebellar fibers

Middle cerebellar peduncle

Inferior olivary nucleus

Olivo-cerebellar fibers

FIGURE 55: Cerebellum 2 — Cerebellar Afferents

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