Hello again everyone! This is Matt from Kenhub, and in this tutorial, we will be looking at the medial rectus muscle of the eye, its origin and insertion, function and innervation and blood supply.
The medial rectus muscle is one of the six extraocular muscles that control eye movements. This muscle is located on the medial aspect of the eyeball. It is also the largest of the extraocular muscles and stronger than its antagonistic pairing – the lateral rectus muscle. The medial rectus muscle along with the other rectus muscles originates from the common tendinous ring also known as the annulus of Zinn which is located at the apex of the orbit around the optic canal.
The annulus of Zinn is formed by the tendons of the four rectus muscles – medial, lateral, superior and inferior. The medial rectus muscle inserts onto the anteromedial surface of the eye. When the eye is at a neutral position, contraction of the medial rectus muscle moves the pupil of the eye inward medially towards the nose. This movement is called adduction.
Innervation of the medial rectus muscle is provided by the inferior branch of the oculomotor nerve – the third cranial nerve. The oculomotor nerve in green is shown here from a lateral view. The continuation of this branch here innervates the medial rectus muscle on the medial aspect of the eye not visible in this image. The medial rectus muscle receives arterial blood supply from two branches of the anterior ciliary arteries which are derived from the ophthalmic artery. In this image, only one of these branches is visible indicated here.
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