Inferior Rectus

Origin, Insertion, Action & Nerve

Attachments explained

The Inferior 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.

Action & function

When the Inferior Rectus contracts, it produces the following movement: Depresses, adducts, and extorts (laterally rotates) 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 Inferior 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 Inferior Rectus, impairing the movements it normally produces (depresses, adducts, and extorts (laterally rotates) the eyeball). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Inferior Rectus (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Inferior 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 Inferior 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.

Inferior Rectus quick facts

Region

Head & Neck

Group

Extraocular

Origin

Inferior part of the common tendinous ring (annulus of Zinn) at the orbital apex

Insertion

Inferior sclera, ~6.5 mm posterior to the corneal limbus

Action

Depresses, adducts, and extorts (laterally rotates) the eyeball

Nerve

Inferior division of the oculomotor nerve (CN III)

Spinal roots

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Frequently asked questions

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