The Spinocerebellar Module

The spinocerebellum (paleocerebellum) is so called because the vermian and intermediate zones receive important inputs from the ventral and dorsal spinocere-bellar tracts. Through these inputs, the cerebellum monitors body position and movement. These zones also receive afferents from the upper extremities via the cuneocerebellar tract. The cerebellum also receives inputs from the contralateral accessory olivary nuclei. The cerebellum integrates this information and projects it to the cerebral cortex via the thalamus. The impulses that travel up to the cerebellar cortex in the ascending spinocerebellar tract are arranged in topographical order. The parts of the body are faithfully relayed in topographical order to the ipsilateral cerebellar cortex.

The spinocerebellum exerts control over axial musculature through the efferent outputs from the vermian cortex and the fastigial nuclei. It controls limb movements through outputs to the globose and emboliform nuclei. Afferent information coming from the cerebellar cortex into the emboliform and globose nuclei is arranged in topographical order. Note that the para-vermian cortical areas project to both nuclei, while the vermian cortex projects to the fastigial nuclei. From the fastigial nuclei, outputs cross to the contralateral vestibular and accessory olivary nuclei, and into the midbrain reticular formation. The fastigial nucleus also projects con-tralaterally to send fastigiospinal fibers down through the spinal cord, where they terminate in the medial ventral horn. The information sent from the cerebellar cortex to the ipsilateral fastigial nucleus is arranged in topographical order. Fibers from the anterior part of the vermian cerebellar cortex enter the fastigial nucleus at its top or rostral end, while those from the posterior vermian cerebellar cortex enter the fastigial nucleus at its caudal end.

The emboliform and globose nuclei (also called anterior and posterior interposed nuclei, respectively) send efferent projections via the superior cerebellar peduncle to the contralateral side of the brain.

Some fibers, the cerebellorubral fibers, ascend and terminate in the red nucleus, while others ascend further to the ventral lateral nucleus of the thalamus. The system consisting of the red nucleus, together with its descending rubrospinal fibers and the primary motor cortex, with its descending corticospinal fibers, together control contralateral spinal ventral horn motoneurons that drive the distal limbs.

Other emboliform and globose nuclear efferents project caudally and descend to the midbrain reticular formation (cere-belloreticular fibers), while others project to the contralateral olivary nuclei. The reticular formation and the accessory olivary nuclei in turn project reciprocally back to the emboliform and globose nuclei.

In summary, the role of the spinocere-bellum is the maintenance of body posture as an antigravity regulatory system. The spinocerebellum controls the level of muscular tension or tone required to maintain posture while standing or moving.

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Lateral Vestibular Nuclei And Red Nuclei


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