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