ⓘ Corticomesencephalic tract. In neuroanatomy, corticomesencephalic tract is a descending nerve tract that originates in the frontal eye field and terminate in th ..

                                     

ⓘ Corticomesencephalic tract

In neuroanatomy, corticomesencephalic tract is a descending nerve tract that originates in the frontal eye field and terminate in the midbrain. Its fibers mediate conjugate eye movement.

                                     

1. Structure

The corticomesencephalic tract originates from the frontal eye field in the caudal part of the middle frontal gyrus and the inferior frontal gyrus Brodmanns 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.

                                     

2. Function

The fibers of the corticomesencephalic tracts are involved in the control of the conjugate eye movement. The fibers to the oculomotor III nucleus control the medial rectus, superior rectus, inferior rectus, and inferior oblique muscles. Fibers to the trochlear IV nucleus control the superior oblique muscle. Fibers to the paramedian pontine reticular formation PPRF project to the abducens VI nucleus, which controls the movement of the lateral rectus muscle. Also, fibers to the paramedian pontine reticular formation mediates the movements with the oculomotor III and trochlear IV nerves through the medial longitudinal fasciculus MLF. The MLF coordinates the interaction between the oculomotor III and the abducens VI nuclei, which create bilateral conjugate horizontal eye movements.

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