MSK - Muscles of the Pectoral Region Flashcards
Images reproduced, with permission, from teachmeanatomy.info
How many muscles lie in the pectoral region?
What are their names?
3
Pectoralis Major
Pectoralis Minor
Serratus Anterior
What is the most superficial muscle of the pectoral region? What is is shaped like?
Pectoralis Major
Fan Shaped
How many heads does the Pectoralis Major have?
What are their names?
Where do they attach?
2 heads
Clavicular head - Attaches to the clavicle
Sternocostal head - Attaches to the sternum and ribs
Fibres from both can be found attaching to the intertubecular groove of the humerus
Where does the Pectoralis Major originate from?
Anterior surface of sternal half of clavicle, anterior half of sternum and as low down as sixth of seventh rib
What actions are the two heads capable of?
What further action is the clavicular head capable of?
Together - Adduction and Medial Rotation of the Humerus
Clavicular Head - Flexion
What nerves innervate the Pectoralis Major?
Where are they derived from?
Medial and Lateral Pectoral nerves
Brachial Plexus
What muscle lies posterior to the Pectoralis Major?
Pectoralis Minor
What shape is the Pectoralis Minor?
Triangular Shape
Where does the Pectoralis Minor originate from?
Where does it attach to?
Anterior surface of ribs 3-5
Attaches to corocoid process of Scapula
What nerve innervates the Pectoralis Minor
Medial Pectoral Nerve
What is the main action of Pectoralis Minor?
Stabilises scapula by drawing it inferiorly and anteriorly against thoracic wall
What muscle is found more laterally in the chest than the Pectoralis Major and Minor muscles and forms the medial wall of the axilla?
Serratus Anterior
Where does the Serratus Anterior originate from?
Where does it attach to?
Serratus Anterior is composed of strip of muscle that originate from ribs 2-8
Attach to costal surface of the medial border of the scapula
(Note: Medial border of costal surface of Scapula has been expertly spray painted in green. Not to be confused with the Acromion which is also shaded a green colour)
What is the Serratus Anterior innervated by?
Long Thoracic Nerve
What is the action of the Serratus Anterior?
Rotates the Scapula which allows abduction of the arm above 90°
Also holds Scapula against thoracic wall (ribcage) which is useful when upper limb reaches anteriorly in actions such as punching. Hence, the Serratus Anterior is the “boxer’s muscle”
What has happened to this individual?
“Winged Scapula”
Damage to the Long Thoracic Nerve
Serratus Anterior no longer innervated, Scapula no longer held against rib cage
