Scalenus Posterior
Neck · Head & Neck
The scalenus posterior is the smallest and most deeply placed of the three scalene muscles of the lateral neck. It arises from the transverse processes of the C5 to C7 vertebrae and descends to insert on the external surface of the second rib, distinguishing it from the anterior and middle scalenes, which reach the first rib. Acting from above, it elevates the second rib to assist inspiration, and acting from below it laterally flexes the neck. It is supplied by the anterior rami of the cervical nerves (C6 to C8). It often blends with the scalenus medius and can be difficult to separate as a distinct muscle.
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)
Set the scalenus posterior apart from its two siblings by its rib target: this is the scalene that reaches the second rib, whereas the anterior and middle scalenes both attach to the first. Fixing that single distinction is the most efficient way to keep the three muscles straight, since they share so much in origin and action.
For its action, reason that a muscle running from the lower cervical transverse processes to the second rib can raise that rib in inspiration or bend the neck to the side when the rib is fixed. Keep it with the scalene group supplied by anterior cervical rami, and remember it is the smallest and deepest of the three, often fused with the middle scalene.
Frequently asked questions
Where is the Scalenus Posterior located?
The Scalenus Posterior is a muscle of the Neck group, located in the Head & Neck.
What is the origin of the Scalenus Posterior?
Transverse processes of C5–C7
What is the insertion of the Scalenus Posterior?
External surface of 2nd rib
What movements does the Scalenus Posterior produce?
Elevates 2nd rib in inspiration; laterally flexes neck
What nerve supplies the Scalenus Posterior?
Anterior rami of cervical nerves (C6–C8)
Is the Scalenus Posterior free to study in OIANS?
The Scalenus Posterior is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Head & Neck is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Scalenus Posterior
Test yourself on Head & Neck muscles with interactive quizzes and flashcards in the free OIANS app.
Quiz yourself → Flashcards Open the OIANS app
Browsing is always free. A one-time Lifetime unlock adds every region's quizzes, flashcards, progress tracking and explore tools.