The inferior rectus muscle is a muscle in the orbit near the eye. It is one of the four

recti 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 ...

in the group of

extraocular muscle 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 ...

s. It originates from the common tendinous ring, and inserts into the anteroinferior surface of the eye. It depresses the eye (downwards).

Structure

The inferior rectus muscle originates from the common tendinous ring (annulus of Zinn). It inserts into the anteroinferior surface of the eye. This insertion has a width of around 10.5 mm. It is around 7 mm from the

corneal limbus The corneal limbus (''Latin'': corneal border) is the border between the cornea and the sclera (the white of the eye). It contains stem cells in its palisades of Vogt. It may be affected by cancer or by aniridia (a developmental problem), amon ...

Blood supply

The inferior rectus muscle is supplied by an inferior muscular branch of the ophthalmic artery. It may also be supplied by a branch of the infraorbital artery. It is drained by the corresponding veins: the inferior muscular branch of the

ophthalmic vein Ophthalmic veins are veins which drain the eye. More specifically, they can refer to: * Superior ophthalmic vein * Inferior ophthalmic vein The inferior ophthalmic vein is a vein of the orbit that - together with the superior ophthalmic vein - ...

, and sometimes a branch of the

infraorbital vein The infraorbital vein is a vein that drains structures of the floor of the orbit. It arises on the face and passes backwards through the orbit alongside infraorbital artery and nerve, exiting the orbit through the inferior orbital fissure to drain i ...

Nerve supply

The inferior rectus muscle is supplied by the inferior 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 of ...

(III).

Development

The inferior rectus muscle develops from the embryonic mesoderm in the orbit of the skull. This is similar 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 ...

Relations

The insertion of the inferior rectus muscle is around 6 mm from the insertion of the medial rectus muscle, and around 8 mm from the insertion of the

lateral rectus muscle Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

. A parasympathetic branch that supplies the

ciliary muscles The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscleSchachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) . in the eye's middle layer, uvea ( vascular layer). It controls accommodation for viewing ...

of the pupil passes close to the inferior rectus muscle.

Variation

Very rarely, the inferior rectus muscle may be congenitally absent. This may cause inferior rectus palsy, where the eye cannot be depressed.

Function

The inferior rectus muscle depresses, adducts, and helps

extort Extortion is the practice of obtaining benefit through coercion. In most jurisdictions it is likely to constitute a criminal offence; the bulk of this article deals with such cases. Robbery is the simplest and most common form of extortion, al ...

the eye. It is the only muscle that is capable of depressing the pupil when it is in a fully abducted position.

Clinical significance

Strabismus

If the inferior rectus muscle is

damaged Damage is any change in a thing, often a physical object, that degrades it away from its initial state. It can broadly be defined as "changes introduced into a system that adversely affect its current or future performance".Farrar, C.R., Sohn, H., ...

, weak, or

paralysed Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 50 ...

, this can cause strabismus. This can lead to elevation of the eye, as the

superior rectus muscle The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is elevation ...

remains stronger. For minor cases, prism glasses can be used to gradually realign the eye. Alternatively for serious cases, it may be surgically corrected by slightly weakening the

(opposite) - this reduces the elevation of the eye, and corrects the strabismus. This procedure may lead to overcorrection of the strabismus, but is otherwise generally successful.

Surgery

Any surgery on the inferior rectus muscle may damage the parasympathetic branches to the

of the pupil. This may cause problems with control of the pupil. Nearby blood vessels and nerves may also be damaged.

Additional images

File:Slide12uu.JPG, Inferior rectus muscle File:Slide2abaa.JPG, Extrinsic eye muscle. Nerves of orbita. Deep dissection.

References

External links

* * ()
Diagram at mun.ca
{{Authority control Muscles of the head and neck Human eye anatomy de:Augenmuskeln#Musculus rectus inferior