Trochlear nerve

The trochlear nerve is the fourth cranial nerve and is the motor nerve of the superior oblique muscle of the eye.

Gross anatomy

Nucleus and cisternal portion

It is the only cranial nerve to exit the brainstem posteriorly, immediately below the inferior colliculus. It then rounds the cerebral peduncles in the ambient cistern coursing, along with the oculomotor nerve, between the superior cerebellar artery and posterior cerebral artery, and pierces the dura in-between the free and attached edge of tentorium cerebelli.

Cavernous sinus portion

Within the cavernous sinus the trochlear nerve is located initially below the oculomotor nerve in the lateral wall of the sinus, although by the time it reaches the superior orbital fissure it is above it (outside the tendinous ring). It is the "Tarts" in the infamous mnemonic.

Orbital portion

Having entered the orbit lateral and superior to the tendinous ring it arches up and medially (see Figure 3) above superior rectus and levator palpebrae superioris to innervate the superior oblique.


Neuroanatomy
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Article Information

rID: 2213
Section: Anatomy
Synonyms or Alternate Spellings:
  • Trochlear nerve (CN IV)
  • Trochlear nerve (IV)

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    Figure 1: brain stem nuclei
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    Figure 2: cavernous sinus
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    Anterior view of ...
    Figure 3: CN IV orbital portion
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