Trochlear nerve

The trochlear nerve controls the superior oblique muscle of the eye, one of the extraocular muscles, the muscles that move the eye. Paralysis of the trochlear nerve results in rotation of the eyeball upward and outward (and, therefore, double vision). The trochlear nerve is the fourth cranial nerve. (The twelve cranial nerves emerge from or enter the skull as opposed to the spinal nerves which emerge from the vertebral column). The trochlear nerve is the only cranial nerve that arises from the back of the brain stem. It follows the longest course within the skull of any of the cranial nerves.

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trochlear nerve n either of the fourth pair of cranial nerves that arise from the dorsal aspect of the brain stem just below the inferior colliculus and supply the superior oblique muscle of the eye with motor fibers

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the fourth cranial nerves (IV), which supplies the superior oblique muscle, one of the muscles responsible for movement of the eyeball in its socket. The action of the trochlear nerve is coordinated with that of the oculomotor and the abducens nerve.

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nervus trochlearis.