Trochlear nucleus
The trochlear nucleus is the motor nucleus of the trochlear nerve. It is located in the medial midbrain.
Structure
The trochlear nucleus is located in the midbrain, at an intercollicular level between the superior colliculus and inferior colliculus. As with all motor nuclei of cranial nerves, it is located near the midline. It is embedded within the medial longitudinal fasciculus. It is situated immediately below the nucleus of the oculomotor nerve .The trochlear nucleus is unique in that its axons run dorsally and cross the midline at the trochlear decussation in the midbrain before emerging from the brainstem posteriorly/dorsally. In other words, trochlear nucleus on one side gives rise to the trochlear nerve on the contralateral side. A lesion of the trochlear nucleus thus affects the contralateral eye, whereas lesions of all other cranial nuclei affect the ipsilateral side.