Nucleus of trochlear nerve

The nucleus of trochlear nerve is situated in the lower midbrain, at the level of the inferior colliculus, specifically within the anterior portion of the periaqueductal gray matter. Being a motor nucleus, it is located near the midline, just inferior to the oculomotor nucleus. Notably, the trochlear and oculomotor nerves are the only cranial nerves with nuclei located within the midbrain.

The trochlear nerve nucleus is classified as a general somatic efferent nucleus. It generates somatic motor nerve fibers that follow an unusual path: after leaving the nucleus, these fibers travel posteriorly, circling around the periaqueductal gray matter, to emerge on the posterior surface of the midbrain. Consequently, the trochlear nerve is the only cranial nerve that arises from the back of the midbrain.

Afferent connections:

The nucleus of trochlear nerve receives several afferent connections:

• Corticonuclear fibers: These upper motor neurons originate from both cerebral hemispheres and synapse with the trochlear nerve nuclei.

• Tectobulbar fibers: The trochlear nerve nuclei receive tectobulbar fibers from the superior colliculus, enabling the relay of information from the visual cortex.

• Medial longitudinal fasciculus (MLF): This structure links the trochlear nerve nucleus to the nuclei of the third, sixth, and eighth cranial nerves, facilitating coordinated eye and head movements.