The Origin(s)

The GSE fibres arise from the trochlear nucleus near nucleus lies near the midline of the midbrain at the level of the inferior colliculus.

The Course

  • Fibres curve laterally and dorsally

  • Exit from the dorsal surface of the brain stem

  • Pass below the inferior colliculus lateral to the crus cerebri

  • Pierce the dura mater to enter the lateral wall of the cavernous venous sinus just below the oculomotor nerve.

  • Enters the orbit through the superior orbital fissure

  • Pass above the common tendinous ring.

  • Within the orbit the trochlear nerve crosses over the levator palpebrae superioris and superior rectus muscles.

Functional Components
  • Predominantly general somatic efferent (motor) to the superior oblique

  • A few afferent fibres from the muscle spindles


Despite its size, this nerve supplies only one muscle - the superior oblique.

Probable cause and sites of injury

Due to its long complicated course, the trochlear nerve is quite vulnerable to injury. Causes include:

•  Midbrain vascular lesions

•  Hydrocephalus with dilatation of the cerebral aqueduct

•  Fracture base of skull

•  Meningeal tumors

•  Cavernous sinus thrombosis

•  Orbital tumors