15.14
Muscles of the Shoulder
The muscles surrounding the shoulder girdle, including the clavicle and scapula, primarily stabilize the scapula. This stable base allows other muscle…
The shoulder muscles provide stability and mobility to the shoulder joint.
The anterior shoulder muscles include the subclavius, pectoralis minor, and serratus anterior.
The subclavius, a small muscle extending from the first rib to the clavicle, stabilizes the clavicle during shoulder movements.
The pectoralis minor, a flat muscle under the pectoralis major, tilts the scapula anteriorly and pulls it inferiorly. It also elevates the thorax, aiding in respiration.
The serratus anterior, a fan-shaped muscle on the thorax's lateral side, protracts the scapula, aiding in punching movements.
The posterior shoulder muscles include the trapezius, levator scapulae, and rhomboid major and minor.
The trapezius, a large triangular muscle, covers the back and neck, inserting on the clavicle and scapula. It elevates, retracts, and rotates the scapula, elevates the clavicle, and extends the neck.
The levator scapulae, an elongated muscle located in the posterior neck, contributes to the elevation and adduction of the scapula.
The major and minor rhomboid muscles help retract the scapula and rotate it medially.
View the full transcript and gain access to JoVE Core videos
Q1: What are the anterior shoulder muscles and what do they do?
The anterior shoulder muscles include the subclavius, pectoralis minor, and serratus anterior. The subclavius stabilizes the clavicle during shoulder movements. The pectoralis minor tilts the scapula anteriorly, pulls it inferiorly, and aids in respiration by elevating the thorax. The serratus anterior, known as the boxer's muscle, protracts the scapula and assists in punching movements.
Q2: How does the serratus anterior contribute to arm movements?
The serratus anterior originates from the first to eighth or ninth ribs and inserts along the superior and inferior angles and medial border of the scapula. This fan-shaped muscle protracts and upwardly rotates the scapula, enabling abduction of the arm. When the scapula is fixed, it elevates the ribs, assisting in punching movements and other dynamic shoulder actions.
Q3: What are the main posterior shoulder muscles?
The posterior shoulder muscles include the trapezius, levator scapulae, and rhomboid major and minor. The trapezius is a large triangular muscle that elevates, retracts, and rotates the scapula while extending the neck. The levator scapulae elevates and adducts the scapula. The rhomboid muscles retract the scapula and rotate it medially.
Q4: How does the trapezius muscle function in shoulder movement?
The trapezius originates from the occipital bone, ligamentum nuchae, and cervical and thoracic vertebrae, inserting on the clavicle and scapula. Its upper fibers elevate the scapula and extend the neck, middle fibers adduct the scapula, and lower fibers depress the scapula. This three-part arrangement allows diverse scapular and neck movements.
Q5: Why is scapular stability important for shoulder function?
The shoulder girdle muscles primarily stabilize the scapula, creating a stable base that allows other muscles to move the humerus effectively. Scapular movements mirror those of the humerus and extend its range of motion. Without simultaneous upward rotation of the scapula, raising the arm above the head would not be feasible.
Q6: What is the role of the subclavius muscle?
The subclavius originates on the first rib and inserts into the lower surface of the lateral clavicle. Its primary function is to stabilize the clavicle during shoulder and arm movements. It also depresses the clavicle and moves it anteriorly, contributing to overall shoulder girdle stability.
Q7: How do the rhomboid muscles affect scapular position?
The rhomboid minor and major originate from the cervical and thoracic vertebrae and insert along the vertebral border of the scapula. These muscles retract the scapula, pulling it medially toward the spine, and rotate it medially. This action is essential for movements requiring scapular adduction and internal rotation.