Serratus anterior
Origin
Upper eight or nine ribs (outer surfaces)
Insertion
Costal surface of scapula (along medial border)
Nerve supply
Long thoracic nerve (branch from roots C5, 6, 7 of brachial plexus).
Action
1. Pulls scapula forwards around chest wall (with pectoralis minor). As a result the upper limb moves forwards as in giving a blow.
2. Forward rotation of scapula (with trapezius). The glenoid cavity is turned upwards and leads to overhead abduction of the arm.
Clinical Notes
The muscle is tested by making the patient place his palms against a wall and pushing against it. If the muscle is paralysed the medial margin of the scapula is lifted off from the ribs. This is called winging of the scapula. Ovahead abduction of the arm is not possible.
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