Corticomesencephalic tract

Structure

The corticomesencephalic tract originates from the frontal eye field in the caudal part of the middle frontal gyrus and the inferior frontal gyrus (Brodmann's area 8). It runs rostral to the pyramidal tract in the posterior limb of the internal capsule. Then, it courses posteriorly toward the nuclei of the oculomotor nerve (III), trochlear nerve (IV) and abducens nerve (VI), the three cranial nerves that mediate eye movements. At the level of the caudal midbrain, corticomesencephalic fibers descend through the tegmentum in the medial lemniscus toward the oculomotor (III) and the trochlear (IV) nuclei on the contralateral (opposite) side. However, the fibers to the abducens (VI) nucleus do not terminate directly onto the nucleus. Instead, they terminate onto the paramedian pontine reticular formation (PPRF). The PPRF contains excitatory “burst” neurons that transmit the pulse to the ipsilateral (the same side of the body) abducens nucleus.