Summary The Trochlear Nerve (CN IV)

The Trochlear Nerve (CN IV)


 It is the smallest cranial nerve, but has the longest intracranial path
 It only contains somatic motor neurones, so has no sensory function

Anatomical course:
 The trochlear nerve begins at the trochlear nucleus and arises from the
posterior surface of the midbrain (only CN to exit from posterior surface)
 It then passes anteriorly and inferiorly in the subarachnoid space before
piercing the dura adjacent to the posterior clinoid process
 It moves along the lateral wall of the cavernous sinus before entering the orbit
via the superior orbital fissure




Motor function:
 The trochlear nerve only innervates one muscle, the superior oblique
 The tendon of the superior oblique muscle is tethered to the superior nasal
aspect of the frontal bone by a fibrous band called the trochlea
 This allows the superior oblique muscle to perform its complex action of
depressing and intorting the eyeball