Inferior rectus muscle
Updates to Article Attributes
The inferior rectus muscle is one of the six extraocular muscles that control eye movements.
Summary
- innervation: inferior branch of the oculomotor nerve (CN III)
- origin: annulus of Zinn (tendinous ring)
- insertion: globe (anterior, inferior surface)
- primary function: one of two ocular depressors
- secondary function: one of the two ocular external rotators
- tertiary function: one of the three ocular adductors
Gross anatomy
Origin
Inferior rectus, along with the other rectus muscles, arises from the annulus of Zinn, the common tendinous ring at the apex of the orbit that surrounds the optic canal 1.
Insertion
Inferior rectus runs anteriorly on the inferior surface of the eye and inserts into the inferior surface of the sclera just posterior to the junction of cornea and sclera 2.
Relations
Inferior rectus is crossed by the inferior oblique muscle, which runs inferior to it as it crosses the floor of the orbit.
Arterial supply
Branches of the ophthalmic artery, itself a branch of the internal carotid artery.
Innervation
Innervated by the oculomotor nerve, which also supplies medial rectus, superior rectus, and inferior oblique muscles.
Action
The primary action of the inferior rectus is to depress the eye (see figure 1) 1. However, because the apex of the orbit is placed medially in the skull, the orbital axis that the inferior rectus runs in does not correspond with the optical axis of the eye in its neutral position. This means that the inferior rectus has secondary actions of adduction and external rotation (see figures 2 and 3).
If the eye is abducted by the lateral rectus such that the optical axis lines up with the orbital axis, the inferior rectus produces ocular depression only, and is solely responsible for this movement. Thus, when the physician testing eye movements first asks the patient to follow their finger laterally then inferiorly in the familiar H-shape, the inferior rectus muscle (and the oculomotor nerve that supplies it) are being directly tested.
If the eye is adducted by the medial rectus, the orbital axis runs almost perpendicular to the optical axis, so the inferior rectus no longer produces effective ocular depression, and instead produces external rotation and adduction.
Etymology
Rectus comes from the Latin rectos, meaning straight 1.
Related pathology
See also
-</ul><h4>Gross anatomy</h4><h5>Origin</h5><p>Inferior rectus, along with the other rectus muscles, arises from the annulus of Zinn, the common tendinous ring at the apex of the orbit that surrounds the <a title="Optic canal" href="/articles/optic-canal">optic canal</a> <sup>1</sup>.</p><h5>Insertion</h5><p>Inferior rectus runs anteriorly on the inferior surface of the eye and inserts into the inferior surface of the <a href="/articles/sclera">sclera</a> just posterior to the junction of <a href="/articles/cornea">cornea</a> and sclera <sup>2</sup>.</p><h5>Relations</h5><p>Inferior rectus is crossed by the <a href="/articles/inferior-oblique-muscle">inferior oblique muscle</a>, which runs inferior to it as it crosses the floor of the orbit.</p><h4>Arterial supply</h4><p>Branches of the <a href="/articles/ophthalmic-artery">ophthalmic artery</a>, itself a branch of the <a href="/articles/internal-carotid-artery-1">internal carotid artery</a>.</p><h4>Innervation</h4><p>Innervated by the <a href="/articles/oculomotor-nerve">oculomotor nerve</a>, which also supplies <a href="/articles/medial-rectus-muscle">medial rectus</a>, <a href="/articles/superior-rectus-muscle">superior rectus</a>, and <a href="/articles/inferior-oblique-muscle">inferior oblique muscles</a>.</p><h4>Action</h4><p>The primary action of the inferior rectus is to depress the eye (see figure 1) <sup>1</sup>. However, because the apex of the orbit is placed medially in the skull, the orbital axis that the inferior rectus runs in does not correspond with the optical axis of the eye in its neutral position. This means that the inferior rectus has secondary actions of adduction and external rotation (see figures 2 and 3).</p><p>If the eye is abducted by the lateral rectus such that the optical axis lines up with the orbital axis, the inferior rectus produces ocular depression only, and is solely responsible for this movement. Thus, when the physician testing eye movements first asks the patient to follow their finger laterally then inferiorly in the familiar H-shape, the inferior rectus muscle (and the oculomotor nerve that supplies it) are being directly tested.</p><p>If the eye is adducted by the medial rectus, the orbital axis runs almost perpendicular to the optical axis, so the inferior rectus no longer produces effective ocular depression, and instead produces external rotation and adduction.</p><h4>Etymology</h4><p>Rectus comes from the Latin <em>rectos</em>, meaning straight <sup>1</sup>.</p><h4>Related pathology</h4><ul><li><a href="/articles/oculomotor-nerve-palsy">oculomotor nerve palsy</a></li></ul><h4>See also</h4><ul><li>- +</ul><h4>Gross anatomy</h4><h5>Origin</h5><p>Inferior rectus, along with the other rectus muscles, arises from the annulus of Zinn, the common tendinous ring at the apex of the orbit that surrounds the <a href="/articles/optic-canal">optic canal</a> <sup>1</sup>.</p><h5>Insertion</h5><p>Inferior rectus runs anteriorly on the inferior surface of the eye and inserts into the inferior surface of the <a href="/articles/sclera">sclera</a> just posterior to the junction of <a href="/articles/cornea">cornea</a> and sclera <sup>2</sup>.</p><h5>Relations</h5><p>Inferior rectus is crossed by the <a href="/articles/inferior-oblique-muscle">inferior oblique muscle</a>, which runs inferior to it as it crosses the floor of the orbit.</p><h4>Arterial supply</h4><p>Branches of the <a href="/articles/ophthalmic-artery">ophthalmic artery</a>, itself a branch of the <a href="/articles/internal-carotid-artery-1">internal carotid artery</a>.</p><h4>Innervation</h4><p>Innervated by the <a href="/articles/oculomotor-nerve">oculomotor nerve</a>, which also supplies <a href="/articles/medial-rectus-muscle">medial rectus</a>, <a href="/articles/superior-rectus-muscle">superior rectus</a>, and <a href="/articles/inferior-oblique-muscle">inferior oblique muscles</a>.</p><h4>Action</h4><p>The primary action of the inferior rectus is to depress the eye (see figure 1) <sup>1</sup>. However, because the apex of the orbit is placed medially in the skull, the orbital axis that the inferior rectus runs in does not correspond with the optical axis of the eye in its neutral position. This means that the inferior rectus has secondary actions of adduction and external rotation (see figures 2 and 3).</p><p>If the eye is abducted by the <a title="Lateral rectus muscle" href="/articles/lateral-rectus-muscle">lateral rectus</a> such that the optical axis lines up with the orbital axis, the inferior rectus produces ocular depression only, and is solely responsible for this movement. Thus, when the physician testing eye movements first asks the patient to follow their finger laterally then inferiorly in the familiar H-shape, the inferior rectus muscle (and the <a title="Oculomotor nerve" href="/articles/oculomotor-nerve">oculomotor nerve</a> that supplies it) are being directly tested.</p><p>If the eye is adducted by the <a title="Medial rectus muscle" href="/articles/medial-rectus-muscle">medial rectus</a>, the orbital axis runs almost perpendicular to the optical axis, so the inferior rectus no longer produces effective ocular depression, and instead produces external rotation and adduction.</p><h4>Etymology</h4><p>Rectus comes from the Latin <em>rectos</em>, meaning straight <sup>1</sup>.</p><h4>Related pathology</h4><ul><li><a href="/articles/oculomotor-nerve-palsy">oculomotor nerve palsy</a></li></ul><h4>See also</h4><ul><li>
Unable to process the form. Check for errors and try again.