Pontocerebellar fibers

The pontocerebellar fibers are the second-order fibers of the corticopontocerebellar tract. They arise from the nuclei pontis as the second leg of the path of the corticopontocerebellar tract (the first part being the corticopontine fibers which synapse in the nuclei pontis), and deecussate (cross-over) in the pons before passing through the middle cerebellar peduncle to reach and terminate in the contralateral posterior lobe of cerebellum (neocerebellum). It is part of a pathway involved in coordination of voluntary movements.

The middle cerebellar peduncle consists entirely of pontocerebellar fibers; it is the largest pathway of the cerebellum.

Anatomy
The fibers are horizontally oriented, forming bundles which pass dorsally through the pons among the nuclei pontis and interweaving with the perpendicularly orietned corticospinal fiber.

Termination
The pontocerebellar fibers terminate throughout the cerebellar cortex except the flocculonodular lobe in an arrangement corresponding to the cortical origin of the pathway: efferents of the primary motor cortex project to the vermis and paravermal zone; efferents of the premotor, somatosensory, and association cortex project to the cerebellar hemisphere cortex. Additionally, the fibers also issue collaterals to the dentate nucleus.

Pathway
The entire pathway begins and ends in the cerebral cortex, and its entire course is the following:

(Motor and sensory areas of) cerebral cortex → corticopontine fibers → (ipsilateral) nuclei pontis (synapse) → pontocerebellar fibers (decussation within pons) → middle cerebellar peduncle → (contralateral) (cerebellar cortex and (collaterals) dentate nucleus of) posterior lobe of cerebellum (synapse) → cerebellothalamic tract → superior cerebellar peduncle → mesencephalon (midbrain) (decussation of tract at level of inferior colliculus) → (ipsilateral) (ventral lateral nucleus of) thalamus → (ipsilateral) motor (cerebral) cortex (predominately premotor cortex and primary motor cortex)

Clinical significance
Damage to the pontocerebellar fibers (or nuclei pontis) will result in contralateral ataxia: due to the double decussation of the pathway along its entire course, it terminates in the motor cortex of the same cerebral hemisphere in which it began; the motor latral corticospinal tract then decussates once during its descend to control movement of the opposite side of the body.