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The inferior rectus muscle is one of the four straight muscles of the orbit responsible for eye movement. 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 primary action of the inferior rectus is to depress the eyeball, but it also works in coordination with other extraocular muscles to control eye movements and adjust the gaze direction. The inferior rectus muscle is innervated by the oculomotor nerve and receives its blood supply from the ophthalmic and infraorbital arteries.
| Characteristics | Values |
|---|---|
| Type | One of the 4 [6] rectus muscles, which are a group of 4 straight muscles of the orbit |
| Function | Controls eye movement in the cardinal directions, primarily depressing the eye (downwards) |
| Secondary Functions | Adduction and external rotation of the eye |
| Origin | Common tendinous ring (also known as the annulus of Zinn) |
| Insertion | Anteroinferior surface of the eye |
| Innervation | Inferior division of the oculomotor nerve (CN III) |
| Blood Supply | Ophthalmic artery and infraorbital artery |
| Drainage | Inferior muscular branch of the ophthalmic vein and sometimes a branch of the infraorbital vein |
| Development | Develops from the embryonic mesoderm in the orbit of the skull |
| Related Conditions | Inferior rectus palsy (inability to depress the eye), strabismus (eye misalignment) |
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What You'll Learn
The inferior rectus muscle is one of the four straight muscles of the orbit
The inferior rectus muscle is a narrow, strap-shaped muscle that extends over the floor of the orbit, passing superior to the infraorbital canal. The primary action of this muscle is to depress the eyeball, causing the cornea and pupil to move inferiorly. This depression of the eyeball is often referred to as downgaze. However, due to the position of the apex of the orbit in relation to the eye, the inferior rectus also has secondary actions of adduction and external rotation.
The inferior rectus muscle is innervated by the oculomotor nerve (CN III), specifically its inferior division, which provides it with general somatic efferent fibres. 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 inferior rectus muscle is involved in controlling the movements of the eyeball and adjusting the direction of gaze, often working in coordination with other extraocular muscles.
The inferior rectus muscle plays a crucial role in eye movements, particularly when a physician is testing for eye movement disorders. During an eye movement test, the patient is asked to follow the physician's finger laterally and then inferiorly in an H-shape pattern. This action directly tests the inferior rectus muscle and the oculomotor nerve that supplies it. Any damage to the oculomotor nerve can result in partial or complete paralysis of the inferior rectus muscle, leading to a condition known as external oculomotor palsy.
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It originates from the common tendinous ring
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 also 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, at the apex of the orbit. The annulus of Zinn is a fibrous thickening of the periosteum from which the rectus muscles originate. It is a funnel-shaped tendinous ring located at the orbital apex and is continuous with the dural sheath of the optic nerve and the periorbita.
The common tendinous ring encircles the superior, medial, and inferior margins of the optic canal and part of the superior orbital fissure. The inferior rectus muscle arises from the inferior part of the common tendinous ring, adjacent to the attachments of the medial, lateral, and superior rectus muscles. The rectus muscles, also known as recti, originate from the annulus of Zinn. This includes the medial, lateral, superior, and inferior rectus muscles.
The annulus of Zinn, or common tendinous ring, is named after Johann Gottfried Zinn (1727-1759), a German anatomist and botanist who became famous for his anatomical research on the eye. His work, "Anatomical Description of the Human Eye" (1755), is considered one of the earliest and best descriptions of the organ and a fundamental work in ophthalmology. The annulus of Zinn serves as the origin of six of the seven extraocular muscles.
The inferior rectus muscle passes along the floor of the orbit, superior to the infraorbital canal, which houses the infraorbital artery. It inserts onto the anteromedial part of the sclera, covered by the inferior oblique muscle. 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 fibers. The primary action of the inferior rectus is the depression of the eyeball, but it also plays a role in adduction and external rotation.
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It attaches to the lower anterior surface of the eyeball
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 also one of the six extraocular muscles that control eye movements. The inferior rectus muscle originates from the common tendinous ring, also known as the annulus of Zinn, and attaches to the lower anterior surface of the eyeball.
The eyeball contains three layers: the outer layer, formed by the cornea and sclera; the middle layer, holding the primary blood supply for the eye and containing the iris and pupil; and the inner layer, which is comprised of the retina. The sclera is the white portion of the eye, making up the back five-sixths of the eye's outer layer. It provides protection for the eye and serves as the attachment for the extraocular muscles, which move the eye. The inferior rectus muscle inserts into the lower part of the sclera, just behind the junction of the cornea and sclera.
The inferior rectus muscle passes along the floor of the orbit, superior to the infraorbital canal, which houses the infraorbital artery. As it inserts onto the anteromedial part of the sclera, the inferior rectus muscle is covered by the inferior oblique muscle. The suspensory ligament of the eyeball is formed by the blended sheaths of the inferior rectus and oblique muscles. This hammock-like sling provides support to the eyeball.
The primary action of the inferior rectus muscle is to depress the eyeball. However, because the apex of the orbit is placed medially in the skull, the inferior rectus also has secondary actions of adduction and external rotation. The inferior rectus muscle works in coordination with other extraocular muscles to control the movements of the eyeball and adjust the direction of the gaze.
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Its primary action is the depression of the eyeball
The inferior rectus muscle is one of the four straight muscles of the orbit responsible for eye movement in the cardinal directions. It is also one of the six extraocular muscles that control eye movements. The inferior rectus muscle originates from the common tendinous ring, also known as the annulus of Zinn, and attaches at the lower anterior surface of the eyeball.
The primary action of the inferior rectus muscle is the depression of the eyeball. This means that it pulls the eye downward without rotating the eye. The inferior rectus muscle works in coordination with other extraocular muscles to control eyeball movements and adjust the direction of the gaze. For example, it works in synergy and opposition with the superior oblique muscle. When the inferior rectus contracts, causing the eye to look down, the superior oblique also contracts to prevent extorsion of the eye.
The inferior rectus muscle passes along the floor of the orbit, superior to the infraorbital canal. As it inserts onto the anteromedial part of the sclera, it is covered by the inferior oblique muscle. In this region, the fascial sheath of the inferior rectus muscle is thickened and fused with the sheath of the inferior oblique muscle. These fused sheaths form the suspensory ligament of the eyeball, a hammock-like sling that provides support to the eyeball.
The inferior rectus muscle is supplied by the oculomotor nerve (CN III), which provides it with general somatic efferent fibers. It receives its arterial blood supply from the ophthalmic artery and the infraorbital artery, which arise from the internal carotid and maxillary arteries, respectively.
The inferior rectus muscle plays a crucial role in eye movement and coordination, working in conjunction with other extraocular muscles to ensure proper eyeball function and gaze direction.
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It is supplied by the inferior division of the oculomotor nerve
The inferior rectus muscle is one of the 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. It originates from the common tendinous ring, also called the annulus of Zinn, and attaches at the lower anterior surface of the eyeball. The primary action of the inferior rectus is depression of the eyeball. It acts in coordination with other extraocular muscles to control the movements of the eyeball and adjust the direction of gaze.
The inferior rectus muscle is supplied by the inferior division of the oculomotor nerve (CN III). The oculomotor nerve is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements of the eye and raise the eyelid. It originates from the midbrain of the brainstem, specifically from the oculomotor nucleus located within the midbrain of the brainstem, ventral to the cerebral aqueduct.
The oculomotor nerve provides motor innervation to several extraocular muscles, including the inferior rectus muscle. It also contains fibres that innervate the intrinsic eye muscles, enabling pupillary constriction and accommodation for near-object focus. The nerve includes axons of type GSE (general somatic efferent), which innervate the skeletal muscle of the inferior rectus muscle, and axons of type GVE (general visceral efferent), which provide preganglionic parasympathetic fibres to the ciliary ganglion.
The inferior division of the oculomotor nerve sends a preganglionic branch to the ciliary ganglion, which is located just behind the eyeball. This preganglionic branch carries parasympathetic nerve fibres that synapse with parasympathetic postganglionic fibres within the ganglion. These postganglionic fibres then supply the intrinsic muscles of the eye, including the inferior rectus muscle.
The inferior rectus muscle receives its arterial blood supply from the ophthalmic artery and infraorbital artery, which arise from the internal carotid and maxillary arteries, respectively. The contraction of the inferior rectus muscle results in three simultaneous actions: depression of the eyeball, adduction, and external rotation.
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Frequently asked questions
The inferior rectus muscle is one of the four rectus muscles, alongside the superior, medial, and lateral rectus muscles. It is also one of the six or seven extraocular muscles that control eye movements.
The inferior rectus muscle is located in the eye. 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 primary action of the inferior rectus muscle is to depress the eyeball. It also works with other extraocular muscles to control the movement of the eyeball and adjust the direction of the gaze.
