Muscles of Eye Movement

Muscles of Eye Movement

A. Movements of the eye

1. Intorsion

• Is a medial (inward) rotation of the upper pole (12 o'clock position) of the cornea, caused by the superior oblique and superior rectus muscles

2. Extorsion

• Is a lateral (outward) rotation of the upper pole of the cornea, caused by the inferior oblique and inferior rectus muscles.

B. Common tendinous ring

• Is a fibrous ring that surrounds the optic canal and the medial part of the superior orbital fissure.
• Is the site of origin of the four rectus muscles of the eye and transmits the following structures:

• Oculomotor, nasociliary, and abducens nerves , which enter the orbit through the superior orbital fissure and the common tendinous ring.
• Optic nerve, ophthalmic artery, and central artery and vein of the retina , which enter the orbit through the optic canal and the tendinous ring.
• Superior ophthalmic vein plus the trochlear, frontal, and lacrimal nerves , which enter the orbit through the superior orbital fissure but outside the tendinous ring.

C. Muscles of the Orbit

Muscle Superior rectus
Origin Common tendinous ring
Insertion Sclera just behind cornea
Nerve Oculomotor
Actions on Eyeball Elevates; intorts

Muscle Inferior rectus
Origin Common tendinous ring
Insertion Sclera just behind cornea
Nerve Oculomotor
Actions on Eyeball Depresses; extorts

Muscle Medial rectus
Origin Common tendinous ring
Insertion Sclera just behind cornea
Nerve Oculomotor
Actions on Eyeball Adducts

Muscle Lateral rectus
Origin Common tendinous ring
Insertion Sclera just behind cornea
Nerve Abducens
Actions on Eyeball Abducts

Muscle Levator palpebrae superioris
Origin Lesser wing of sphenoid above and anterior to optic canal
Insertion Tarsal plate and skin of upper eyelid
Nerve Oculomotor, sympathetic
Actions on Eyeball Elevates upper eyelid

Muscle Superior oblique
Origin Body of sphenoid bone above optic canal
Insertion Sclera beneath superior rectus
Nerve Trochlear
Actions on Eyeball Turns center of cornea downward and laterally; rotates upper pole of cornea inward (intorsion); depresses adducted eye

Muscle Inferior oblique
Origin Floor of orbit lateral to lacrimal groove
Insertion Sclera beneath lateral rectus
Nerve Oculomotor
Actions on Eyeball Turns center of cornea upward and laterally; rotates upper pole of cornea outward (extorsion); elevates adducted eye

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