Serratus Anterior

Shoulder & Scapula · Upper Limb

The Serratus Anterior is found among the Shoulder & Scapula muscles of the Upper Limb. It arises from External surfaces of ribs 1–8 (fleshy digitations) and attaches to Anterior (costal) surface of medial border of scapula. It is responsible for several movements: Protracts and upwardly rotates scapula; holds scapula against thoracic wall. Its nerve supply is the Long thoracic nerve (C5, C6, C7).

Origin, Insertion, Action & Nerve

Origin

External surfaces of ribs 1–8 (fleshy digitations)

Insertion

Anterior (costal) surface of medial border of scapula

Action

Protracts and upwardly rotates scapula; holds scapula against thoracic wall

Nerve

Long thoracic nerve (C5, C6, C7)

Attachments explained

The Serratus Anterior 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

External surfaces of ribs 1–8 (fleshy digitations)

Insertion

Anterior (costal) surface of medial border of scapula

Action & function

When the Serratus Anterior contracts, it produces the following movements: Protracts and upwardly rotates scapula; holds scapula against thoracic wall.

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 Serratus Anterior receives its nerve supply from the Long thoracic nerve (C5, C6, C7). This nerve carries fibres from spinal segment(s) C5, C6, C7.

Because a muscle can only contract when its nerve is intact, injury to the Long thoracic nerve or to its spinal roots (C5, C6, C7) can weaken or paralyse the Serratus Anterior, impairing the movements it normally produces (protracts and upwardly rotates scapula). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Serratus Anterior (the OIANS method)

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