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Anatomy Atlases: Atlas of Microscopic Anatomy: Section 1 - Cells Atlas of Microscopic Anatomy: Section 17 - Central Nervous System

Plate 17.337 Pons- Mesencephalic Junction

Ronald A. Bergman, Ph.D., Adel K. Afifi, M.D., Paul M. Heidger, Jr., Ph.D.
Peer Review Status: Externally Peer Reviewed

Trochlear nerve coronal

Plate 17.337 Pons- Mesencephalic Junction

Human, 10% formalin, Pal-Weigert, 2.9 x.


Brachium conjunctivum: Massive outflow tract of the cerebellum. Fibers are seen just prior to and beginning decussation. Fibers project, after decussation, into the red nucleus and ventrolateral nucleus of the thalamus. Lesions in this tract result in a disorder of coordinated movement.

Pontocerebellar tract: The same structure seen at more caudal levels.

Corticospinal, corticopontine, corticobulbar tracts: The same structures seen at more caudal levels. Cut in cross section as they descend to lower caudal levels.

Pontine nuclei: Scattered between pontocerebellar fibers and the corticospinal, corticopontine, and corticobulbar tracts.

Brachium pontis: Axons of pontine nuclei on their way to the cerebellum.

Medial lemniscus: Continuation of the same structure seen at more caudal levels.

Spinal lemniscus: Continuation of the same structure seen at more caudal levels. Contains spinothalamic and spinotectal fibers.

Lateral lemniscus: Contains cochlear fibers. Located laterally and dorsally on its way to the inferior colliculus and medial geniculate body. Concerned with audition.

Trochlear (CN IV) nerve: Seen exiting from the dorsal aspect of the midbrain after decussating. The fourth cranial nerve supplies the superior oblique extraocular muscle. The only cranial nerve to decussate (cross) completely prior to leaving the neuraxis.

Central tegmental tract: Compact fiber bundle located medial to the brachium conjunctivum. Carries fibers from the midbrain tegmentum, red nucleus, and periaqueductal gray matter to the inferior olivary complex. Note change in position of this tract in more caudal levels.

Medial longitudinal fasciculus: Continuation of same structure seen at more rostral and more caudal levels.

Decussation of trochlear (CN IV) nerve: Axons of neurons in the trochlear nucleus seen decussating prior to exit from the dorsal surface of the neuraxis.  

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