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Trochlear nerve

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noun, plural: trochlear nerves

The cranial nerve that innervates the superior oblique muscle of the eye


Cranial nerves are paired nerves that emerge from the brain and the brainstem. They supply the motor pathways between organs in the face and the upper body, and account for detecting and processing various sensations. One of the cranial nerves is the trochlear nerve, which is also referred to as the fourth cranial nerve or cranial nerve IV (CN IV).

The trochlear nerve is the pair of nerves that innervates the superior oblique muscle (i.e. the fusiform muscle originating in the upper median of the orbit of the eye, and is responsible for abducting, depressing, and internally rotating the eye). Lesions of this nerve will result in the rotation of the eyeball upward and outward (and double vision). It is the smallest cranial nerve based on the number of axons it contains. Nevertheless, it has the greatest intracranial length compared with other cranial nerves. It can also be characterized by being the only cranial nerve that exits from the dorsal of the brainstem. In humans, it is derived from the basal plate of the midbrain during embryonic development.

This cranial nerve works together with the cranial nerve III (oculomotor nerve) and the cranial nerve VI (abducens nerve) in controlling movements of the eyeballs.


  • cranial nerve IV (CN IV)
  • fourth cranial nerve
  • pathetic nerve

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