The Trochlear Nerve

Anatomy > Gray's Anatomy of the Human Body > IX. Neurology > 5d. The Trochlear Nerve (N. Trochlearis; Fourth Nerve)

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

The Trochlear Nerve

(N. Trochlearis; Fourth Nerve)

The trochlear nerve (Fig. 776), the smallest of the cranial nerves, supplies the Obliquus superior oculi. It arises from a nucleus situated in the floor of the cerebral aqueduct, opposite the upper part of the inferior colliculus.

From its origin it runs downward through the tegmentum, and then turns backward into the upper part of the anterior medullary velum. Here it decussates with its fellow of the opposite side and emerges from the surface of the velum at the side of the frenulum veli, immediately behind the inferior colliculus.

The nerve is directed across the superior cerebellar peduncle, and then winds forward around the cerebral peduncle, immediately above the pons, pierces the dura mater in the free border of the tentorium cerebelli, just behind, and lateral to, the posterior clinoid process, and passes forward in the lateral wall of the cavernous sinus, between the oculomotor nerve and the ophthalmic division of the trigeminal.

It crosses the oculomotor nerve, and enters the orbit through the superior orbital fissure. It now becomes the highest of all the nerves, and lies medial to the frontal nerve. In the orbit it passes medialward, above the origin of the Levator palpebrae superioris, and finally enters the orbital surface of the Obliquus superior.

http://www.wikimd.org/images/gray/large/image776.gif

FIG. 776– Nerves of the orbit. Seen from above. (Picture From the Classic Gray's Anatomy)

In the lateral wall of the cavernous sinus the trochlear nerve forms communications with the ophthalmic division of the trigeminal and with the cavernous plexus of the sympathetic.

In the superior orbital fissure it occasionally gives off a branch to the lacrimal nerve. It gives off a recurrent branch which passes backward between the layers of the tentorium cerebelli and divides into two or three filaments which may be traced as far as the wall of the transverse sinus.

Function

The trochlear nerve provides motor supply to the superior oblique muscle of the eye,The trochlear nerve carries axons of type GSE, general somatic efferent, which innervate skeletal muscle of the superior oblique muscle.

The superior oblique muscle ends in a tendon that passes through a fibrous loop, the trochlea, located anteriorly on the medial aspect of the orbit. Trochlea means “pulley” in Latin; the fourth nerve is named after this structure.

Additional images

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  Dura mater and its processes exposed by removing part of the right half of the skull, and the brain.

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  Hind- and mid-brains; postero-lateral view.

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  Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.

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  Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ.

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  Trochlear nerve.Deep dissection.Superior view.

External links

• hier-449 at NeuroNames

• oph/697 at eMedicine

- "Trochlear Nerve Palsy"

• MedEd at Loyola Grossanatomy/h_n/cn/cn1/cn4.htm

• lesson3 at The Anatomy Lesson by Wesley Norman (Georgetown University)

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• cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University)

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• Animations of extraocular cranial nerve and muscle function and damage (University of Liverpool)
• Trochlear nerve at Neurolex

Gray's Anatomy

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