Superior rectus muscle
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- innervation: superior branch of the oculomotor nerve (CN III)
- origin: annulus of Zinn (tendinous ring)
- insertion: globe (anterior, superior surface)
- primary function: one of two ocular elevators
- secondary function: one of the two ocular internal rotators
- tertiary function: one of the three ocular adductors
Superior rectus, along with the other rectus muscles, arises from the annulus of Zinn, the common tendinous ring at the apex of the orbit that surrounds the optic canal 1.
Superior rectus is closely related to levator palpebrae superioris, which runs parallel and immediately superior to it and is responsible for elevation of the eyelid.
The primary action of the superior rectus is to elevate the eye (see figure 1) 1. However, because the apex of the orbit is placed medially in the skull, the orbital axis that the superior rectus runs in does not correspond with the optical axis of the eye in its neutral position. This means that the superior rectus has secondary actions of adduction and internal rotation (see figures 2 and 3).
If the eye is abducted by the lateral rectus such that the optical axis lines up with the orbital axis, the superior rectus produces ocular elevation only, and is solely responsible for this movement. Thus, when the physician testing eye movements first asks the patient to follow their finger laterally then superiorly in the familiar H-shape, the superior rectus muscle (and the oculomotor nerve that supplies it) are being directly tested.
If the eye is adducted by the medial rectus, the orbital axis runs almost perpendicular to the optical axis, so the superior rectus no longer produces effective ocular elevation, and instead produces internal rotation and adduction.
Rectus comes from the Latin rectos, meaning straight 1.
- 1. Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. (2013) ISBN: 9781451119459
- 2. Netter FH. Atlas of Human Anatomy. (2018) ISBN: 9780323393225
- 3. Gray's basic anatomy. Churchill Livingstone. ISBN:1455710784. Read it at Google Books - Find it at Amazon
- 4. Imaging of the Head and Neck. Thieme. (2012) ISBN:3131505311. Read it at Google Books - Find it at Amazon