The nucleus of the trochlear nerve exists in the caudal midbrain. This cranial nerve is unique from all others because it’s fibers cross the midline prior to exiting the brainstem and they exit from the dorsal surface of the brainstem.
The trochelar nerve is a somatic motor neuron.
CN IV controls the superior oblique muscle which abducts, depresses and internally rotates the eye. If damaged the eye drifts upward leading to vertical diplopia. This manifests when reading the newspaper or walking down stairs.
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