7.5 Muscles of the Pectoral Girdle and Upper Limbs
7.5 Muscles of the Pectoral Girdle and Upper Limbs
Learning Objectives
By the end of this section, you will be able to:
- Identify the muscles of the pectoral girdle and upper limbs
- Identify the movement and function of the pectoral girdle and upper limbs
Muscles of the shoulder and upper limb can be divided into four groups: muscles that stabilize and position the pectoral girdle, muscles that move the arm, muscles that move the forearm, and muscles that move the wrists, hands, and fingers. The pectoral girdle, or shoulder girdle, consists of the lateral ends of the clavicle and scapula, along with the proximal end of the humerus, and the muscles covering these three bones to stabilize the shoulder joint. The girdle creates a base from which the head of the humerus, in its ball-and-socket joint with the glenoid fossa of the scapula, can move the arm in multiple directions.
Muscles That Position the Pectoral Girdle
Muscles that position the pectoral girdle are located either on the anterior thorax or on the posterior thorax (Figure 7.12 and Table 7.6). The anterior muscles include the subclavius, pectoralis minor, and serratus anterior. The posterior muscles include the trapezius, rhomboid major, and rhomboid minor. When the rhomboids are contracted, your scapula moves medially, which can pull the shoulder and upper limb posteriorly.
|
Prime mover |
Origin |
Insertion |
Movement |
|
Subclavius |
First rib |
Inferior surface of clavicle |
Depression of the clavicle; stabilizes the clavicle during shoulder movement |
|
Levator scapula |
Transverse processes C1-4 |
Medial border of scapula |
Elevation of the scapula; cervical side flexion |
|
Pectoralis minor |
Ribs 3-5 |
Coracoid process of the scapula |
Stabilizes the scapula against the rib cage by pulling anteriorly; assists with inhalation |
|
Serratus anterior |
Lateral aspects of ribs 1-9 |
Anterior surface of lateral border of scapula |
Scapular protraction |
|
Trapezius |
Occipital bone; nuchal ligament; spinous process of C7-T12 |
Lateral ⅓ of clavicle; spine of scapula; acromion process |
Upper fibers – scapular elevation; cervical side flexion Middle fibers – scapular retraction Lower fibers – scapular depression |
|
Rhomboid major |
Thoracic vertebrae T2-5 |
Medial border of scapula |
Scapular retraction; scapular downward rotation |
|
Rhomboid minor |
C7 and T1 |
Medial border of scapula |
Scapular retraction; scapular downward rotation |
Muscles That Move the Humerus
Similar to the muscles that position the pectoral girdle, muscles that cross the shoulder joint and move the humerus bone of the arm include both axial and scapular muscles (Figure 7.13 and Table 7.7). The two axial muscles are the pectoralis major and the latissimus dorsi. The pectoralis major is thick and fan-shaped, covering much of the superior portion of the anterior thorax. The broad, triangular latissimus dorsi is located on the inferior part of the back, where it inserts into a thick connective tissue sheath cal