Extraocular muscles

From WikiLectures

Extraocular muscles (schematic) by Eshaan Mehmi

There are 7 extra-ocular muscles - 6 of each responsible for moving the eye ball and 1 is responsible for raising the eyelids.

Function of eye muscles

The extra-ocular muscles are:

Levator palpebrae Superioris (most superior extra-ocular muscle)

  • Origin: lesser wing of sphenoid bone (superior-anterior to optic canal)
  • Insertion: superior tarsus of the eyelid
    Lateral view of Eye muscles
    Frontal Section
  • Function: raising the eyelid
  • Innervation: superior division of the oculomotor nerve (CN 3).
  • Unique feature: some of its inferior fibers are smooth muscle fibers - help with eyelid elevation. Innervated by post-ganglionic sympathetic fibers.

Rectus Muscles (superior, medial and lateral)

Origin: the common tendinous ring (all of the muscles)

Insertion: sclera (posterior to corneoscleral junction)

Function: the axis of the orbit and the axis of the eyeball aren’t the same

  • Superior rectus: moves the eyeball superiorly and medially.
  • Inferior rectus: moves the eyeball inferiorly and medially  
  • Lateral rectus: abduction of eyeball
  • Medial rectus: adduction of eyeball

Innervation:

  • All except lateral rectus: oculomotor n. (CN 3)
  • Lateral rectus: abducent nerve (CN 6)

Superior oblique: medial to the levator palpebrae superioris

  • Origin: body of the sphenoid bone.
  • Insertion: tendon pass through trochlea insert in sclera (deep to superior rectus).
  • Function: abducts, depresses and rotates eyeball medially.
  • Innervation: trochlear nerve (CN 4).

Inferior oblique

  • Origin: anterior floor of the orbit (maxilla).
  • Insertion: Runs posterolaterally crossing the inferior rectus insert in sclera (deep to lateral rectus)
  • Function: abducts, elevates and rotated eyeball laterally
  • Innervation: oculomotor nerve (CN 3)