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Anatomy and function of the superior rectus muscle.
Hey everyone! This is Nicole from Kenhub, and in this tutorial, we're going to look at one of the extraocular muscles of the eye – the superior rectus muscle.
The superior rectus muscle is one of the six extraocular muscles of the eye for controlling eye movement. The superior rectus muscle produces the following actions – elevation, intorsion and adduction of the eye.
During adduction of the eye, the superior rectus produces adduction. Now, adduction refers to the movement towards the median plane of the body, and if we look at this diagram and where the muscles attach, you can imagine the muscle pulling the eye inward as if you’re trying to look at your nose. So, I’m just going to draw this arrow just to help you visualize it.
In adduction, the superior rectus also helps with elevation, which I’m going to illustrate with my arrow here – I trust you all know what elevation is – if you forget, it’s just as the arrow says, it just raises the eye upwards – and intorsion which is inward rotation of the eye. Now don’t forget that internal rotation is different from adduction where the eye rotates inward on a horizontal plane, for example, from left to right, whereas internal rotation is the inward turning of the eye on a vertical axis which I’m just going to draw here, so clockwise/anti-clockwise on a vertical plane.
So now we know that during adduction of the eye, the superior rectus produces adduction, elevation and intorsion; however, during abduction of the eye, the superior rectus only produces elevation.
The superior rectus muscle originates from the common tendinous ring, also known as the annulus of Zinn, that surrounds the optic nerve at the apex of the orbit, and if we look at our diagram here, we can see that the muscles come together in the annulus of Zinn, and a fun fact, the annulus of Zinn was named after Johann Gottfried Zinn who, in addition to observing the anatomy of the eye, was also a botanist.
The superior rectus inserts on the anterior superior surface of the eye. As you can see here in this image, the superior rectus muscle is a straight muscle hence its name, rectus, which means “straight” in Latin.
The superior rectus receives arterial blood supply from two of the anterior ciliary arteries derived from the muscular branches of the ophthalmic artery. So, in this image, you can see the muscular branches of the ophthalmic artery which enter the orbit through the optic canal. Also, just note that the branches of the ophthalmic artery are the main suppliers of the extraocular muscles.
Innervation of the superior rectus muscle is provided by the superior branch of the oculomotor nerve – cranial nerve three – which you can see here highlighted in green.
The oculomotor nerve enters the orbit via the superior orbital fissure and it might be interesting to note that other structures pass through here, too – very important structures such as the trochlear nerve and the abducens nerve – and it’s quite important to note clinically as often if you have a severe orbital trauma, you can damage quite a lot of the structures in this fissure.