The superior rectus muscle is a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

in the

orbit In celestial mechanics, an orbit (also known as orbital revolution) 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 ...

. It is one of the

extraocular muscles The extraocular muscles, or extrinsic ocular muscles, are the seven extrinsic muscles of the eye in human eye, humans and other animals. Six of the extraocular muscles, the four recti muscles, and the superior oblique muscle, superior and inferior ...

. It is innervated by the superior division of the

oculomotor nerve The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements o ...

(III). In the primary position (looking straight ahead), its primary function is

elevation The elevation of a geographic location (geography), ''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 equipotenti ...

, 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. 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 ipsilateral

(III). Each superior rectus muscle is innervated by contralateral oculomotor nucleus in the mesencephalon.

Relations

The superior rectus muscle is related to the other

, particularly to the medial rectus muscle 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, and helps intort (rotate the superior pole of the eye 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

(III). This may be

congenital A birth defect is an abnormal condition that is present at childbirth, birth, regardless of its cause. Birth defects may result in disability, disabilities that may be physical disability, physical, intellectual disability, intellectual, or dev ...

, often with a familial genetic link, or acquired, most often caused by head injuries.

Overreaction

Local anaesthetics used in

cataract surgery Cataract surgery, also called lens replacement surgery, is the removal of the natural lens (anatomy), lens of the human eye, eye that has developed a cataract, an opaque or cloudy area. The eye's natural lens is usually replaced with an artific ...

may weaken the inferior rectus muscle, 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 Apert syndrome is a form of acrocephalosyndactyly, a congenital disorder characterized by malformations of the skull, face, hands and feet. It is classified as a branchial arch syndrome, affecting the first Pharyngeal arch, branchial (or pharyn ...

. This causes a reduced ability to elevate the eye. It may be treated with eye surgery that uses parts of the medial rectus muscle 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:Slide4abab.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection. File:Slide6abab.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