Sternalis

Origin, Insertion, Action & Nerve

Attachments explained

The Sternalis 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 Sternalis contracts, it produces the following movements: Inconstant variant; may tense the pectoral fascia (no significant functional role).

As part of the Shoulder & Scapula group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The Sternalis receives its nerve supply from the Intercostal nerves (or pectoral nerves), variable.

Because a muscle can only contract when its nerve is intact, injury to the Intercostal nerves can weaken or paralyse the Sternalis, impairing the movements it normally produces (inconstant variant). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Sternalis (the OIANS method)

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

Sternalis quick facts

Region

Upper Limb

Group

Shoulder & Scapula

Origin

Manubrium of the sternum or clavicle

Insertion

Xiphoid process, pectoral fascia, lower ribs, costal cartilages, or rectus sheath

Action

Inconstant variant; may tense the pectoral fascia (no significant functional role)

Nerve

Intercostal nerves (or pectoral nerves), variable

Spinal roots

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Frequently asked questions

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