Scalenus Posterior

Neck · Head & Neck

The Scalenus Posterior is found among the Neck muscles of the Head & Neck. It arises from Transverse processes of C5–C7 and attaches to External surface of 2nd rib. It is responsible for several movements: Elevates 2nd rib in inspiration; laterally flexes neck. Its nerve supply is the Anterior rami of cervical nerves (C6–C8).

Origin, Insertion, Action & Nerve

Origin

Transverse processes of C5–C7

Insertion

External surface of 2nd rib

Action

Elevates 2nd rib in inspiration; laterally flexes neck

Nerve

Anterior rami of cervical nerves (C6–C8)

Attachments explained

The Scalenus Posterior 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

Transverse processes of C5–C7

Insertion

External surface of 2nd rib

Action & function

When the Scalenus Posterior contracts, it produces the following movements: Elevates 2nd rib in inspiration; laterally flexes neck.

As part of the Neck 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 Scalenus Posterior receives its nerve supply from the Anterior rami of cervical nerves (C6–C8). This nerve carries fibres from spinal segment(s) C6, C8.

Because a muscle can only contract when its nerve is intact, injury to the Anterior rami of cervical nerves or to its spinal roots (C6, C8) can weaken or paralyse the Scalenus Posterior, impairing the movements it normally produces (elevates 2nd rib in inspiration). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Scalenus Posterior (the OIANS method)

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