Overview
This lecture reviews the four main muscles of the pectoral region, their origins, insertions, and functions in moving and stabilizing the upper limb.
Muscles of the Pectoral Region
- The pectoral region lies on the anterior chest wall and contains four muscles: pectoralis major, pectoralis minor, serratus anterior, and subclavius.
- These muscles are involved in moving and stabilizing the arm and scapula.
Pectoralis Major
- Pectoralis major is the most superficial pectoral muscle and has two heads: clavicular and sternal costal.
- The clavicular head originates from the clavicle; the sternal costal head originates from the sternum, upper six costal cartilages, and external oblique aponeurosis.
- Both heads insert at the lateral lip of the bicipital groove of the humerus.
- The muscle adducts and medially rotates the arm.
- The sternal costal head extends the arm at the shoulder and is active during a push-up.
- The clavicular head flexes the arm at the shoulder.
Pectoralis Minor
- Pectoralis minor lies beneath pectoralis major, originating from ribs 3–5, and inserts into the coracoid process of the scapula.
- It pulls the scapula against the thoracic wall, stabilizing it.
Serratus Anterior
- Serratus anterior is found along the ribcage sides, with branches from ribs 1–8 or 1–9 (often two from rib 2).
- It inserts on the costal surface of the scapula's medial border.
- The muscle holds the scapula against the ribcage and pulls it forward and around (important for punching).
- It enables scapular rotation beyond 90°, allowing arm abduction above the head.
Subclavius
- Subclavius runs beneath the clavicle, originating from the first rib and its costal cartilage and inserting into the clavicle’s underside.
- It anchors, depresses, and stabilizes the clavicle.
- It protects the underlying brachial plexus in case of clavicle fracture.
Key Terms & Definitions
- Pectoralis Major — superficial chest muscle with clavicular and sternal costal heads; moves the arm at the shoulder.
- Pectoralis Minor — small chest muscle under pectoralis major; stabilizes and anchors the scapula.
- Serratus Anterior — muscle along the ribs; holds scapula to ribcage and aids in arm lifting.
- Subclavius — small muscle under the clavicle; stabilizes and protects the clavicle and brachial plexus.
- Brachial Plexus — nerve bundle providing sensory and motor function to the upper limb.
Action Items / Next Steps
- Review diagrams of the four pectoral muscles and their attachments.
- Watch the next video in the muscle series for further upper limb muscle coverage.