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The Oculomotor Nerve

The oculomotor nerve is the third of the twelve cranial nerves.

Anatomy

It consists of both afferent and efferent visual sensory fibers. The word afferent means toward the centre, as in from a peripheral area of a limb to the central nervous system.

The word efferent is the opposite of afferent, meaning away from the centre and toward the periphery; when the stimulus is carried back to the brain from a peripheral area.

Recommended video: Oculomotor, trochlear and abducens nerves
Course of the oculomotor, abducens and trochlear nerves.

Efferent Pathway

The pathway for the efferent fibers is the following (from the initiation in the brain to the termination in the periphery):

Origins

The origin of the primary efferent oculomotor nerve fibers is the nucleus of the oculomotor nerve that exists within the superior colliculus of the encephalic tract, or the brainstem as it is more commonly known.

Oculomotor nucleus - lateral-left view

Oculomotor nucleus - lateral-left view

Secondary efferent oculomotor nerve fibers also contribute to the oculomotor nerve from the accessory nucleus of the oculomotor nerve also known as the Edinger-Westphal nucleus, which is situated adjacent to the primary nucleus mentioned above.

Edinger-Westphal nucleus - lateral-left view

Edinger-Westphal nucleus - lateral-left view

Pathway & Innervation

The primary and secondary fibers bind together and exit the skull through the superior orbital fissure. After that, the primary fibers provide motor innervation for all the extraocular muscles except the superior oblique muscle and lateral rectus muscle, allowing the eye to move within the orbit.

Oculomotor nerve - lateral-left view

Oculomotor nerve - lateral-left view

The secondary fibers branch off at the level of the ciliary ganglion and synapse there. They then continue on to innervate:

  • the ciliary body
  • the Iris
  • the sphincter pupillae muscle which contract the pupil
  • the dilator pupillae muscle which dilate the pupil

Ciliary body

Ciliary body

Afferent Pathway

The pathway for the afferent fibers is the following (from the stimulatory cells in the periphery to the final synapse in the brain): exactly the opposite of the efferent pathway.

Summary

The oculomotor nerve is the third of the twelve cranial nerves and consists of both afferent and efferent visual sensory fibers. The primary efferent fibers originate in the nucleus of the oculomotor nerve, exit the skull through the superior orbital fissure and innervate all the extraocular muscles, except superior oblique and lateral rectus.

The secondary efferent fibers originate from the Edingar-Westphal nucleus, also leave the skull through the superior orbital fissure and innervate the ciliary body, iris, sphincter pupillae, and dilator pupillae.

The afferent pathway is eactly opposite to the efferent pathway, starting from the stimulatory cells in the periphery and reaching the brain. 

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Show references

Reference:

  • Frank H. Netter: Atlas der Anatomie, 5th Edition (Bilingual Edition: English and German), Saunders, Chapter 1, Plate 89, 114-115, 117 and 120, Published 2010.

Author:

  • Dr. Alexandra Sierosławska

Illustrators:

  • Oculomotor nucleus - lateral-left view - Paul Kim
  • Edinger-Westphal nucleus - lateral-left view - Paul Kim
  • Oculomotor nerve - lateral-left view - Paul Kim
  • Ciliary body - Paul Kim
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Related Atlas Images

Oculomotor, trochlear and abducens nerves

Nerves of the orbit

12 cranial nerves

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