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Muscles and movements of the shoulder girdle.
Hello again, everyone! It’s Matt from Kenhub, and in this tutorial, we will discuss the muscles and movements of the shoulder girdle.
The shoulder girdle consists of two bones: the scapula, and the clavicle (or the collar bone), and the muscles that attach to and move these bones. They are the rhomboids, trapezius, subclavius, pectoralis minor, and levator scapulae muscles.
The rhomboid muscles are two diamond-shaped muscles of the shoulder girdle, both extend from the vertebral column to the medial border of the scapula. They lie over the autochthonous back muscles but under the trapezius. In this area, they are both palpable and often visible.
The rhomboid muscles are divided into the rhomboid major and the rhomboid minor muscle.
Usually, there is a small space between both rhomboid muscles. However, in some cases, one may find one, single blended muscle instead. Both major and minor rhomboids perform the same movement. Their contraction causes a craniomedial movement of the scapula, known as adduction and elevation.
At the same time, the inferior angle of the scapula is moved towards the vertebral column, known as rotation. That movement mainly supports lowering of the elevated arm.
Another function of the rhomboid musculature is the stabilization of the scapula during both rest and arm movement.
The trapezius muscle is a triangular, flat muscle of the shoulder girdle and is divided into three parts: the descending or superior part, the transverse or middle part, and the ascending or inferior part.
The trapezius has numerous tasks. It stabilizes and secures the shoulder blade at the thorax. It moves the shoulder blade medially and rotates it outward. In addition, the descending part causes elevation of the scapula, while the ascending part depresses this bone.
The subclavius muscle is a short muscle of the shoulder girdle. Due to its location (lying behind the pectoralis major) and relatively small size, the muscle is hardly palpable.
The main task of this muscle is the act of stabilization of the clavicle in the sternoclavicular joint during movements of the shoulder and arm.
The pectoralis minor is a fan-shaped muscle of the shoulder girdle. It is located under the pectoralis major, and with that muscle forms the anterior wall of the axilla where the contracted muscle can be easily palpated.
The pectoralis minor has two main functions. First, it pulls the scapula anteriorly and inferiorly towards the ribs, abduction and depression respectively. This leads to a dorsomedial movement of the inferior angle of the scapula. This movement is both helpful when retracting the elevated arm as well as moving the arm posteriorly behind the back.
Second, the pectoralis minor elevates the third to fifth ribs, given a fixed scapula, and expands the rib cage. By those means, it can also serve as an accessory muscle during inspiration.
The levator scapulae is a long muscle of the shoulder girdle. The upper part of this muscle lies under the splenius capitis and sternocleidomastoid muscles, and it’s lower part under the trapezius.
Only the middle part of the levator scapulae remains uncovered in the lateral cervical region, and for that reason, the muscle can be most easily palpated in this area.
As the name indicates, the main function of the levator scapulae is the elevation of the scapula. While elevating, it simultaneously pulls the entire scapula medially. This movement is helpful when bringing the elevated arm back to the neutral position.
In addition, the muscle also moves the inferior angle away from the back, causing a small upward tilt of the scapula. If the scapula is fixed, a contraction of the levator scapulae leads to the bending of the cervical vertebral column to the side, known as lateral flexion.