Logan Steele
The inferior rectus muscle is one of the four straight muscles of the orbit responsible for the movement of the eye in the cardinal directions. It is one of the six extraocular muscles that control eye movements. The inferior rectus muscle originates from the common tendinous ring, also called the annulus of Zinn, and attaches to the lower anterior surface of the eyeball. The primary action of the inferior rectus is the depression of the eyeball, but it also helps in adduction and external rotation.
| Characteristics | Values |
|---|---|
| Muscle type | One of the four straight muscles of the orbit |
| Muscle group | Extraocular muscles |
| Muscle shape | Narrow and strap-shaped |
| Muscle origin | Common tendinous ring (annulus of Zinn) |
| Muscle insertion | Anteroinferior surface of the eye |
| Muscle insertion width | 10.5 mm |
| Distance from corneal limbus | 7 mm |
| Blood supply | Ophthalmic artery, infraorbital artery |
| Nerve supply | Inferior division of the oculomotor nerve (CN III) |
| Veins for drainage | Inferior muscular branch of the ophthalmic vein, branch of the infraorbital vein |
| Embryonic development | Embryonic mesoderm |
| Function | Depresses, adducts, and exorts the eye |
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Origin and insertion
The inferior rectus muscle is one of the four rectus muscles and six extraocular muscles that control eye movements. It is a narrow, strap-shaped muscle of the orbit that extends over the floor of the orbit. The inferior rectus muscle originates from the common tendinous ring, also called the annulus of Zinn, and attaches at the lower anterior surface of the eyeball. The common tendinous ring is an oval band of connective tissue located at the apex of the orbit, anterior to the optic foramen and the medial part of the superior orbital fissure. The upper and lower areas of the common tendinous ring are thickened bands, sometimes referred to as the upper and lower tendons or limbs. The inferior rectus muscle is joined to the lower tendon or limb of the common tendinous ring, adjacent to the attachments of the medial, lateral, and superior recti muscles.
The inferior rectus muscle inserts into the anteroinferior surface of the eye, specifically into the inferior surface of the sclera just posterior to the junction of the cornea and sclera. 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. The width of the insertion is approximately 10.5 mm, and it is located around 7 mm from the corneal limbus. As the inferior rectus muscle courses anterolaterally across the floor of the orbit, its middle part is thickened and then gradually thinned into a tendon. The tendon ends by inserting obliquely on the anteromedial surface of the eyeball, below the limbus of the cornea.
The inferior oblique muscle crosses over the inferior rectus muscle as it inserts onto the anteromedial part of the sclera, and the fascial sheaths of these two muscles blend together. The blended sheaths then attach to the tarsal plate of the inferior eyelid via the inferior check ligament, which is an anterior expansion of the fused sheaths. The inferior rectus muscle is supplied by the inferior division of the oculomotor nerve (CN III), which enters its superior surface and provides it with general somatic efferent fibres. It receives its arterial blood supply from the ophthalmic artery and the infraorbital artery, which arise from the internal carotid and maxillary arteries, respectively.
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Blood supply
The inferior rectus muscle is supplied with blood by the muscular branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery. The ophthalmic artery, which arises from the internal carotid artery, supplies blood to the inferior rectus muscle through its inferior muscular branch. Additionally, the infraorbital artery, which arises from the maxillary artery, may also contribute to the blood supply of the inferior rectus muscle.
The inferior rectus muscle is one of four rectus muscles, along with the superior, medial, and lateral rectus muscles, which are all extraocular muscles. These muscles originate from the common tendinous ring, also known as the annulus of Zinn, and insert into the globe or eyeball. The ophthalmic artery and the nasociliary nerve pass through the annulus of Zinn, providing blood supply and innervation to the surrounding structures.
The arterial blood supply to the inferior rectus muscle is drained by corresponding veins, including the inferior muscular branch of the ophthalmic vein and, in some cases, a branch of the infraorbital vein. These veins play a crucial role in removing deoxygenated blood and maintaining proper blood circulation in the region.
Surgery on the inferior rectus muscle can be complicated due to the presence of nearby blood vessels and nerves. Damage to these blood vessels during surgery can disrupt the blood supply to the extraocular muscles and the anterior segment of the eye, leading to potential complications. Therefore, surgeons must exercise caution to avoid compromising these vital blood vessels during surgical procedures involving the inferior rectus muscle.
The inferior rectus muscle is also associated with the inferior check ligament, which attaches to the tarsal plate of the lower eyelid. This ligament plays a role in enabling the inferior gaze by coordinating eye movements with eyelid position. The muscle and its associated structures work together to ensure the proper functioning of the eye and its surrounding mechanisms.
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Innervation
The inferior rectus muscle is one of the four rectus muscles and six extraocular muscles that control eye movements. It originates from the common tendinous ring, also known as the annulus of Zinn, and inserts into the anteroinferior surface of the eye. The primary action of the inferior rectus muscle is to depress the eye downwards.
The innervation of the inferior rectus muscle is provided by the oculomotor nerve (CN III), specifically its inferior division. This nerve enters the muscle on its superior surface, supplying it with general somatic efferent fibres. The oculomotor nerve is responsible for the movement of the eye and innervates other muscles involved in eye movement, including the medial rectus, superior rectus, and inferior oblique muscles.
The oculomotor nerve, along with other nerves and blood vessels, passes through the oculomotor foramen, which is enclosed by the tendinous ring. The optic nerve and ophthalmic artery enter the oculomotor foramen from the optic canal, while the superior and inferior divisions of the oculomotor nerve, the abducens nerve, and the nasociliary nerve enter from the superior orbital fissure.
The nerve to the inferior rectus muscle also has a branch known as the caudad branch of the oculomotor nerve. By drawing the eyeball cephalad during the cranial expansion phase, a stretch can be effected. This nerve is crucial for the coordination of eye movements and eyelid position, ensuring the lowering of the eyelid during a downward gaze.
The inferior rectus muscle receives its blood supply from the ophthalmic artery and the infraorbital artery, which arise from the internal carotid and maxillary arteries, respectively. The innervation provided by the oculomotor nerve and its branches is essential for the proper functioning of the inferior rectus muscle and the overall coordination of eye movements.
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Function
The inferior rectus muscle is one of the four rectus muscles, along with the superior, medial, and lateral rectus muscles. These four rectus muscles are straight muscles of the orbit that control the movement of the eye in the cardinal directions. The inferior rectus muscle is primarily responsible for depressing or pushing the eyeball downwards. It originates from the common tendinous ring, also known as the annulus of Zinn, and attaches to the lower anterior surface of the eyeball.
The common tendinous ring is an oval band of connective tissue located at the apex of the orbit, encircling the superior, medial, and inferior margins of the optic canal. The inferior rectus muscle, along with the other rectus muscles, arises from the common tendinous ring and runs anteriorly on the inferior surface of the eye. The muscle then inserts into the anteroinferior surface of the eye, specifically onto the anteromedial part of the sclera, just posterior to the junction of the cornea and sclera. This insertion is typically around 6-8 mm from the insertions of the other rectus muscles.
The inferior rectus muscle has a width of approximately 10.5 mm and is located about 7 mm from the corneal limbus. It is supplied by the inferior division of the oculomotor nerve (CN III), which provides it with general somatic efferent fibers. Additionally, the muscle receives its arterial blood supply from the ophthalmic artery and the infraorbital artery, which arise from the internal carotid and maxillary arteries, respectively.
The contraction of the inferior rectus muscle produces three simultaneous actions: depression, adduction, and external rotation of the eye. It is the only muscle capable of depressing the pupil when it is in a fully abducted position. The inferior rectus muscle works in coordination with other extraocular muscles, such as the superior oblique muscle, to control the complex movements of the eyeball and adjust the direction of gaze.
In summary, the inferior rectus muscle is a crucial component of the eye's extraocular muscles, primarily responsible for depressing the eyeball and coordinating its movements in different directions. It originates from the common tendinous ring and inserts into the anteroinferior surface of the eye, receiving its nerve supply from the oculomotor nerve and arterial supply from the ophthalmic and infraorbital arteries.
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Associated pathologies
The inferior rectus muscle is one of the four rectus muscles, which are a group of straight muscles responsible for eye movement in the cardinal directions. These muscles, along with the superior and inferior oblique muscles, are known as the extraocular muscles. The inferior rectus muscle is responsible for depressing the eye downwards.
The inferior rectus muscle may be congenitally absent, though this is very rare. This condition can cause inferior rectus palsy, where the eye cannot be depressed. Strabismus, or wandering eye, is another pathology associated with the inferior rectus muscle. This can be caused by damage, weakness, or paralysis of the muscle, leading to elevation of the eye as the superior rectus muscle remains stronger.
In cases of minor strabismus, prism glasses can be used to gradually realign the eye. More severe cases may require surgical correction, which involves weakening the superior rectus muscle to reduce the elevation of the eye. While generally successful, this procedure may lead to overcorrection of strabismus. Surgery on the inferior rectus muscle carries the risk of damaging the parasympathetic branches to the ciliary muscles of the pupil, resulting in problems with pupil control. Nearby blood vessels and nerves may also be damaged during surgery.
Congenital absence of the inferior rectus muscle is a rare condition that can cause apparent inferior rectus palsy, particularly when no other cause can be identified. This condition has been successfully managed through surgery in conjunction with intramuscular botulinum toxin injections, leading to significant improvement in function and cosmesis.
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Frequently asked questions
The inferior rectus muscle is a muscle in the orbit near the eye. It is one of the four rectus muscles and one of six extraocular muscles that control eye movements.
The inferior rectus muscle originates from the common tendinous ring, also known as the annulus of Zinn.
The primary function of the inferior rectus muscle is to depress the eye downwards. It also adducts and helps extort the eye.
The inferior rectus muscle is supplied by the inferior division of the oculomotor nerve (CN III) and receives its arterial blood supply from the ophthalmic artery and the infraorbital artery.
If the inferior rectus muscle is damaged, weak, or paralysed, it can cause strabismus, leading to an elevation of the eye as the superior rectus muscle remains stronger. In minor cases, prism glasses can be used to realign the eye, while serious cases may require surgical correction.
