The trochlear nerve (cranial nerve IV) innervates the superior oblique muscle in the superior orbital fissure. It plays a primary role in oculomotor control. It depresses and intorts the eye, pulling it laterally. The trochlear nerve acts in conjunction with the oculomotor nerve to enable eye movement in all directions.
The nucleus of the trochlear nerve is located in the caudal midbrain below aqueduct and the nucleus of the oculomotor nerve. The axon of the trochlear nerve runs dorsally and crosses the midline before it leaves the brainstem, so that lesions of the nucleus affect the contralateral eye. This contrasts with all other cranial nuclei lesions, which affect the ipsilateral side. It is necessary for normal saccadic eye movement, as well as visual search. It is the common efferent pathway for brain systems that control eye movement and provides for the necessary muscular response. The trochlear nerve receives input from subcortical systems mediated...
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