Pontocerebellar fibers
The pontocerebellar fibers are the second-order neuron fibers of the corticopontocerebellar tracts that cross to the other side of the pons and run within the middle cerebellar peduncles, from the pons to the contralateral cerebellum.[1] They arise from the pontine nuclei as the second part of the corticopontocerebellar tract (the first part being the corticopontine fibers which synapse in the pontine nuclei), and decussate (cross-over) in the pons before passing through the middle cerebellar peduncles to reach and terminate in the contralateral posterior lobe of the cerebellum (neocerebellum).[2] The middle cerebellar peduncle consists entirely of pontocerebellar fibers and is the largest pathway of the cerebellum.[2] The fibers are horizontally oriented, forming bundles which pass dorsally through the pons among the pontine nuclei and interweave with the perpendicularly oriented corticospinal fibers.[2] The entire pathway begins and ends in the cerebral cortex, and its entire course is the following:[2] (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) Damage to the pontocerebellar fibers (or pontine nuclei) 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 lateral corticospinal tract then decussates once during its descent to control movement of the opposite side of the body.