Medial Rectus
Extraocular · Head & Neck
The Medial Rectus is a Head & Neck muscle within the Extraocular group. Originating at Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex, it inserts at Medial sclera, ~5.5 mm posterior to the corneal limbus. Functionally, it adducts the eyeball. It is innervated by the Inferior division of the oculomotor nerve (CN III).
Origin, Insertion, Action & Nerve
Origin
Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex
Insertion
Medial sclera, ~5.5 mm posterior to the corneal limbus
Action
Adducts the eyeball
Nerve
Inferior division of the oculomotor nerve (CN III)
Attachments explained
The Medial Rectus is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex
Insertion
Medial sclera, ~5.5 mm posterior to the corneal limbus
Action & function
When the Medial Rectus contracts, it produces the following movement: Adducts the eyeball.
As part of the Extraocular group of the Head & Neck, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Medial Rectus receives its nerve supply from the Inferior division of the oculomotor nerve (CN III).
Because a muscle can only contract when its nerve is intact, injury to the Inferior division of the oculomotor nerve can weaken or paralyse the Medial Rectus, impairing the movements it normally produces (adducts the eyeball). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Medial Rectus (the OIANS method)
OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Medial Rectus, work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.
Most students remember the Medial Rectus fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.
Medial Rectus quick facts
- Region
- Head & Neck
- Group
- Extraocular
- Origin
- Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex
- Insertion
- Medial sclera, ~5.5 mm posterior to the corneal limbus
- Action
- Adducts the eyeball
- Nerve
- Inferior division of the oculomotor nerve (CN III)
- Spinal roots
- —
Frequently asked questions
Where is the Medial Rectus located?
The Medial Rectus is a muscle of the Extraocular group, located in the Head & Neck.
What is the origin of the Medial Rectus?
Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex
What is the insertion of the Medial Rectus?
Medial sclera, ~5.5 mm posterior to the corneal limbus
What movements does the Medial Rectus produce?
Adducts the eyeball
What nerve supplies the Medial Rectus?
Inferior division of the oculomotor nerve (CN III)
Is the Medial Rectus free to study in OIANS?
The Medial Rectus is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Head & Neck is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Medial Rectus
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