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Nerve Tracts in the Anterior Brainstem

Surgical Correlation


Nerve tracts in the anterior brainstem. The midbrain crus cerebri contains descending cortical motor fibers that form the corticospinal, corticobulbar, and corticopontine tracts. The latter synapse on deep pontine nuclei, which then send second-order pontocerebellar fibers across the midline to enter the middle cerebellar peduncle and terminate in the contralateral cerebellum. This cortico-ponto-cerebellar pathway helps to influence and maintain coordinated motor function between the cerebrum (primarily frontal lobe) and cerebellum. The corticospinal tract descends through the basis pons and enters the medullary pyramid before decussating within the pyramidal decussation to descend into the spinal cord. The right trochlear nerve can be seen wrapping around the cerebral peduncle from its origin on the dorsal surface of the midbrain. The trigeminal nerves emerge from the anterolateral pons, while the abducens and facial-vestibulocochlear nerve bundles emerge, respectively, from the anterior and lateral pontomedullary junction.  (Image courtesy of PA Rubino)