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An example of trapezius function is an overhead press. When activating together, the upper and lower fibers also assist the middle fibers (along with other muscles such as the rhomboids) with scapular retraction/adduction. The trapezius also assists in abduction of the shoulder above 90 degrees by rotating the glenoid upward.
The rhomboids work collectively with the levator scapulae muscles to elevate the medial border of the scapula, downwardly rotating the scapula with respect to the glenohumeral joint. Antagonists to this function (upward rotators of the scapulae) are the serratus anterior and lower fibers of the trapezius.
The fibers converge to a single tendon to insert onto the olecranon process of the ulna (though some research indicates that there may be more than one tendon) [5] and to the posterior wall of the capsule of the elbow joint where bursae (cushion sacks) are often found.
The large rhombus-shaped muscle, located under the trapezius muscle, in the upper part of the thoracic region of the back, and the small muscle, in the same way, participate in the movement of the scapula. [4] Their functions are the following: [1] [2] [3] Drawing scapula superomedially; Supporting scapula; Rotating glenoid cavity inferiorly
Levator scapulae forms part of the latter group together with rhomboid major, rhomboid minor, serratus anterior, and trapezius. The trapezius evolved separately, but the other three muscles in this group evolved from the first eight or ten ribs and the transverse processes of the cervical vertebrae (homologous to the ribs).
The glenohumeral joint has been analogously described as a golf ball (head of the humerus) sitting on a golf tee (glenoid fossa). [5] The rotator cuff compresses the glenohumeral joint during abduction of the arm, an action known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words ...
It is formed by a dense band of fibers, conical in form, with its base directed upward. It is attached by its apex to a rough impression at the base of the coracoid process on the scapula , medial to the trapezoid ligament ; above, by its expanded base, to the conoid tubercle on the under surface of the clavicle , and to a line proceeding ...
Fusiform muscles have fibers that run parallel to the length of the muscle, and are spindle-shaped. [19] For example, the pronator teres muscle of the forearm. Unipennate muscles have fibers that run the entire length of only one side of a muscle, like a quill pen. For example, the fibularis muscles.