Hello everyone! This is Matt from Kenhub, and in this tutorial, we will discuss one of the six extraocular muscles of the eye – the inferior rectus muscle.
The inferior rectus muscle is one of the six extraocular muscles of the eye that control eye movement. The inferior rectus is a straight muscle that originates from the common tendinous ring also known as the annulus of Zinn which is found at the apex of the orbit around the optic canal indicated here by an arrow. The common tendinous ring is formed by the tendons of the rectus muscles.
The inferior rectus muscle inserts onto the anterior, inferior surface of the eye on the sclera – the white of the eye – about six millimeters posterior to the corneal limbus indicated by the green circle which is the border between the cornea and the sclera. When the eye is in a neutral position, the inferior rectus muscle is responsible for the following movements of the eye: Extorsion which is outward or lateral rotation, adduction which is medial movement towards the midline, and depression which is movement inferiorly. During adduction of the eye, the inferior rectus muscle is again responsible for depression, extorsion and adduction of the eye. During abduction, however, which is the lateral movement of the eye away from the midline, the inferior rectus muscle is responsible for the depression of the eye.
Nerve supply to the inferior rectus muscle is provided by the inferior branch of the oculomotor nerve – cranial nerve three – highlighted in green in the image. The ocular motor nerve innervates four of the six extraocular muscles. Arterial blood supply to the inferior rectus is provided by muscular branches of the ophthalmic artery shown in green and specifically the branches running inferiorly. Additionally, the inferior rectus muscle receives a branch of the infraorbital artery. The infraorbital artery is highlighted in green in the image.
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