Serratus Posterior Superior

Thorax · Trunk

The Serratus Posterior Superior is a Trunk muscle within the Thorax group. It arises from Ligamentum nuchae and spinous processes of C7–T3 and attaches to Superior borders of ribs 2–5, lateral to their angles. Functionally, it elevates ribs 2–5, aiding inspiration. Innervation is provided by the Anterior rami of T2–T5 (intercostal nerves).

Origin, Insertion, Action & Nerve

Origin

Ligamentum nuchae and spinous processes of C7–T3

Insertion

Superior borders of ribs 2–5, lateral to their angles

Action

Elevates ribs 2–5, aiding inspiration

Nerve

Anterior rami of T2–T5 (intercostal nerves)

Attachments explained

The Serratus Posterior Superior 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

Ligamentum nuchae and spinous processes of C7–T3

Insertion

Superior borders of ribs 2–5, lateral to their angles

Action & function

When the Serratus Posterior Superior contracts, it produces the following movement: Elevates ribs 2–5, aiding inspiration.

As part of the Thorax group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The Serratus Posterior Superior receives its nerve supply from the Anterior rami of T2–T5 (intercostal nerves). This nerve carries fibres from spinal segment(s) T2, T5.

Because a muscle can only contract when its nerve is intact, injury to the Anterior rami of T2–T5 or to its spinal roots (T2, T5) can weaken or paralyse the Serratus Posterior Superior, impairing the movements it normally produces (elevates ribs 2–5, aiding inspiration). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Serratus Posterior Superior (the OIANS method)

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