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Serratus anterior muscle

Contents

Anatomy and supply

The serratus anterior muscle is a fan-shaped muscle at the lateral wall of the thorax. Its main part lies deep under the scapula and the pectoral muscles. It is easy to palpate between the pectoralis major and latissimus dorsi muscles. In athletic bodies the muscle may be even visible to the naked eye along the ribs underneath the axilla.

The serratus anterior muscle originates at the 1st to 9th rib and inserts at the ventral surface of the medial border of the scapula. Due to its course it has a “serrated” or “saw-toothed” appearance. The muscle is further divided into three parts:

  • Superior part: 1st to 2nd rib → superior angle of the scapula
  • Intermediate part: 2nd to 3rd rib → medial border of the scapula
  • Inferior part: 4th to 9th rib → medial border and inferior angle of the scapula. This part is the most prominent and powerful one.
  • The innervation is supplied by the long thoracic nerve (C5-7), a branch of the brachial plexus.

Function

The contraction of the entire serratus anterior leads to a ventrolateral movement of the scapula along the ribs. Due to the pull of the inferior part at the lower scapula the shoulder joint is shifted superiorly. This shifting now enables to lift the arm above 90° (elevation). In contrast the superior part depresses the scapula and thus acts antagonistically. Another function of the serratus anterior is the active stabilization of the scapula within the shoulder. Finally in a fixed scapula the muscle lifts the ribs and acts as an accessory inspiratory muscle.

Serratus posterior superior muscle
Recommended video: Serratus posterior superior muscle
Origins, insertions, innervation and function of the serratus posterior superior muscle.

Pathology

A damage of the long thoracic nerve can lead to a functional loss of the serratus anterior. Common causes are operations in the axilla (e.g. lymph node removal), a compression through the carrying of heavy loads (e.g. backpack) and trauma. Typical symptoms are having trouble to elevate the arm and a generally unstable shoulder. Another classic sign is the medial “wing-like” tilting of the scapula (scapula alata).

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Show references

References:

  • M. Schünke/E. Schulte/U. Schumacher: Prometheus – LernAtlas der Anatomie – Allgemeine Anatomie und Bewegungssystem, 2.Auflage, Thieme Verlag (2007), S.294-295
  • J. E. Muscolino: The muscular system manual – The skeletal muscles of the human body, 2.Auflage, Elsevier Mosby (2005), S.214-217
  • P. Berlit: Klinische Neurologie, 3.Auflage, Springer Verlag (2011), S.345

Author:

  • Achudhan Karunaharamoorthy

Illustrators:

  • Serratus anterior muscle - Yousun Koh 
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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