The superior rectus muscle is a muscle in the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...

. It is one of the

extraocular muscles The extraocular muscles (extrinsic ocular muscles), are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the oth ...

. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § ...

, although it also contributes to intorsion and adduction. It is associated with a number of medical conditions, and may be weak, paralysed, overreactive, or even congenitally absent in some people.

Structure

The superior rectus muscle originates from the

annulus of Zinn The common tendinous ring, also known as the annulus of Zinn, or annular tendon, is a ring of fibrous tissue surrounding the optic nerve at its entrance at the apex of the orbit. It is the common origin of the four recti muscles of the group of e ...

. It inserts into the anterosuperior surface of the eye. This insertion has a width of around 11 mm. It is around 8 mm from the corneal limbus.

Nerve supply

The superior rectus muscle is supplied by the superior division of the oculomotor nerve (III).

Relations

The superior rectus muscle is related to the other

, particularly to the

medial rectus muscle The medial rectus muscle is a muscle in the orbit near the eye. It is one of the extraocular muscles. It originates from the common tendinous ring, and inserts into the anteromedial surface of the eye. It is supplied by the inferior division of th ...

and the lateral rectus muscle. The insertion of the superior rectus muscle is around 7.5 mm from the insertion of the medial rectus muscle, around 7.1 mm from the insertion of the lateral rectus muscle, and around 7.9 from the corneal limbus. There is an intermuscular septum between it and the lateral rectus muscle.

Variation

Variations of the superior rectus muscle is rare. It may rarely have two muscle bellies parallel to each other. More rarely, it may be congenitally absent.

Function

The superior rectus muscle elevates,

adducts An adduct (from the Latin ''adductus'', "drawn toward" alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all co ...

, and helps intort (rotate medially) the eye.

Clinical significance

Testing

The superior rectus muscle is the only muscle that is capable of elevating the eye when it is in a fully abducted position.

Exophthalmos

Much of the venous drainage of the orbit and the extraocular muscles passes close to the superior rectus muscle. Obstruction to this venous drainage can cause venous congestion in the eye, which may cause exophthalmos (bulging eye ball). This may be shown with CT scans.

Weakness and paralysis

The superior rectus muscle may be weakened or paralysed by problems with nerve conduction of the oculomotor nerve (III). This may be congenital, often with a familial genetic link, or acquired, most often caused by

head injuries A head injury is any injury that results in trauma to the skull or brain. The terms ''traumatic brain injury'' and ''head injury'' are often used interchangeably in the medical literature. Because head injuries cover such a broad scope of inju ...

Overreaction

Local anaesthetics used in cataract surgery may weaken the

inferior rectus muscle The inferior rectus muscle is a muscle in the orbit near the eye. It is one of the four recti muscles in the group of extraocular muscles. It originates from the common tendinous ring, and inserts into the anteroinferior surface of the eye. It ...

, despite efforts to use minimal anaesthetic and to avoid placing the needle into the muscle. Weakness of the inferior rectus muscle may strengthen the superior rectus muscle, causing it to be overreactive. This may elevate the eye, and prevent its use in normal vision. Treatment may involve eye surgery that weakens or repositions the superior rectus muscle, which generally has good outcomes.

Absence

Very rarely, the superior rectus muscle may be congenitally absent. This may be caused by Apert syndrome. This causes a reduced ability to elevate the eye. It may be treated with eye surgery that uses parts of the

and the lateral rectus muscle to restore the functions normally performed by the superior rectus muscle.

Additional images

File:Gray891.png, The right eye in sagittal section, showing the fascia bulbi (semidiagrammatic). File:Trochlear and frontal nerves.jpg, Superior rectus muscle File:Slide2uu.JPG, Superior rectus muscle File:Slide1abaa.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide2abaa.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide3abab.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide4abab.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide5abab.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide6abab.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide7abab.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide8ababa.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection.

References

External links

* * {{Authority control Muscles of the head and neck Human eye anatomy de:Augenmuskeln#Musculus rectus superior