Serratus Posterior Superior
Thorax · Trunk
The serratus posterior superior is a thin, flat muscle of the intermediate layer of the back, lying deep to the rhomboids in the upper thorax. It arises from the ligamentum nuchae and the spinous processes of the seventh cervical through the third thoracic vertebrae, and its fibres pass downward and laterally to insert onto the superior borders of the second to fifth ribs, lateral to their angles. By pulling these upper ribs upward it elevates them and is traditionally regarded as an accessory muscle of inspiration. It is supplied by the anterior rami of T2 to T5, the upper 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)
Pair serratus posterior superior with serratus posterior inferior as mirror-image respiratory muscles: the superior lies high and pulls the upper ribs up for inspiration, while the inferior lies low and pulls the lower ribs down. The downward-lateral direction of the superior fibres, running from cervical and upper thoracic spines to ribs 2 to 5, makes its rib-elevating action easy to deduce.
Fix its innervation as anterior rami, the intercostal nerves of T2 to T5, which distinguishes it from the dorsally innervated deep back muscles it lies among. Because the nerve levels correspond to the ribs it inserts on, remembering the insertion on ribs 2 to 5 immediately recovers the segmental nerve supply.
Frequently asked questions
Where is the Serratus Posterior Superior located?
The Serratus Posterior Superior is a muscle of the Thorax group, located in the Trunk.
What is the origin of the Serratus Posterior Superior?
Ligamentum nuchae and spinous processes of C7–T3
What is the insertion of the Serratus Posterior Superior?
Superior borders of ribs 2–5, lateral to their angles
What movements does the Serratus Posterior Superior produce?
Elevates ribs 2–5, aiding inspiration
What nerve supplies the Serratus Posterior Superior?
Anterior rami of T2–T5 (intercostal nerves)
Is the Serratus Posterior Superior free to study in OIANS?
The Serratus Posterior Superior 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 Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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