Superior Cerebellar Peduncle (Brachium conjunctivum)
Most of the efferent cerebellar pathways run through the superior cerebellarpeduncle. The only afferent bundle en-tering it is the anterior spinocerebellar tract. The efferent fibers of the superior cerebellar peduncle enter the midbrain tegmentum at the level of the inferior colliculi and cross in the decussation of the superior cerebellarpeduncle (B5) to the opposite side, wherethey divide into a descending (B6) and an ascending limb (B7). The descending fiber bundles originate from the fastigial nucleus (B8) and the globose nucleus (B9). They ter-minate in the medial nuclei of the reticular formation (B10) in pons and medulla ob-longata, where they synapse to form the ret-iculospinal tract. Thus, cerebellar impulsesare transmitted to the spinal cord via two pathways, namely, the reticulospinal tract and the vestibulospinal tract. From both tracts, interneurons affect the anterior horn cells.
The fibers of the stronger ascending limb originate predominantly from the dentate nucleus (B11), but partly also from the em-boliform nucleus. They terminate in two areas: (1) in the red nucleus (B12), its sur-roundings, and various nuclei of the mid-brain tegmentum (Edinger – Westphal nu-cleus, accessory oculomotor nucleus, Dark-shevich’s nucleus, etc.) that connect the cerebellum to the extrapyramidal system, and (2) in the dorsal thalamus (B13) from where the impulses are passed on to the cerebral cortex, mainly to the motor cortex.
These connecting tracts create a large neu-ronal circuit; cerebellar impulses affect the cerebral cortex via brachium conjunctivum and thalamus. The cerebral cortex, in turn, affects the cerebellum via the corticopon-tocerebellar and cortico-olivocerebellar systems. Thus, motor cortex and cerebellum are under mutual control.
Anterior spinocerebellar tract (Gowers’tract) (B14). The fibers originate in the pos-terior horn where fibers primarily from the tendon organs synapse. The postsynaptic bundles run crossed or uncrossed; however, they do not enter the inferior cerebellar peduncle but extend as far as the upper margin of the pons, where they turn and enter through the superior cerebellar peduncle (C). They terminate as mossy fibers in vermis and intermediate zone of the anterior lobe and in the uvula.