Shoulder Muscles with a Direct Relationship with the Rib Cage

Shoulder Muscles with a Direct Relationship with the Rib Cage

The SCM muscle originates from the lateral aspect of the mastoid process and, via a thin aponeurosis, from the lateral half of the superior nuchal line. It inserts on the superior anterior surface of the manubrium sterni and the medial third of the clavicle. The side of the SCM muscle tilts the head to the side and rotates it contralaterally. It also helps flex the cervical spine. With the head fixed, the muscles work together to help with chest elevation and inspiration. The suprahyoid muscles (i.e., digastric, stylohyoid, mylohyoid, and geniohyoid) are important because they work in coordination with the infrahyoid muscles (i.e., sternohyoid, sternothyroid, thyroid, and homohyoid), which have direct attachments to the shoulder girdle. The suprahyoid muscles are active in mandibular depression, hyoid elevation, swallowing and chewing. The infrahyoid muscles are active in hyoid depression, laryngeal elevation and depression, speech and chewing. The homohyoid, one of the infrahyoid muscles, has two bellies that meet at an angle as an intermediate tendon. The upper abdomen originates from the lower border of the hyoid bone and descends to the intermediate tendon. This tendon is wrapped in a deep cervical fascia that extends down to the collarbone and first rib. The lower abdomen descends from this tendon to join the superior scapular margin, near the scapular notch and occasionally the superior transverse scapular ligament. Its actions include hyoid depression during prolonged inspiratory efforts and tension of the lower deep cervical fascia. The pectoralis major muscle originates from the sternal half of the clavicle, a region that approaches from the first to the seventh rib along the center of the anterior sternum and costal cartilages, and the aponeurosis of the external abdominal oblique. Variations include a muscle slide that merges with the SCM. The site of insertion of this muscle is the lateral lip of the intertubercular sulcus along the anterior superior portion of the humerus. The pectoralis major muscle mainly adducts and internally rotates the humerus. It can also aid in shoulder flexion, deep inspiration, and support body weight during crutches. The pectoralis minor muscle originates from the upper margins and outer surfaces of the three to five (sometimes two to four) ribs near the cartilage and fascia that lines the respective intercostal muscles. The insertion sites for this muscle are the medial border and the superior surface of the coracoid process of the scapula. Variations include the insertion extending along the coracoacromial ligament or along the coracohumeral ligament to the humerus. The pectoralis minor muscle mainly tilts the scapula forward and helps the serratus anterior to bring the scapula forward around the chest. Together with the levator scapula and rhomboids, the pectoralis minor helps rotate the scapula and depress the shoulder. The pectoralis minor muscle can also aid in extreme inspiration. The subclavian muscle originates at the junction of the first rib and its cartilage, anterior to the costoclavicular ligament, and attaches to the lower surface of the middle third of the clavicle. Variations include the insertion extending to the coracoid process. The subclavian muscle can be involved by pulling the shoulder down and forward. It may also be active in stabilizing the clavicle against the sternoclavicular disc. The serratus anterior muscle arises from the outer surfaces and upper edges of the upper 8-10 ribs. Variations include a combined origin with the external intercostals or the external oblique abdominal muscle. A combined insertion with the levator scapulae muscle was also observed. The site of insertion of this muscle is the costal surface of the medial margin of the scapula. The anterior serratus muscle mainly abducts and rotates the scapula so that the glenoid fossa faces upward. This muscle also helps in elevation or depression, is able to move the chest posteriorly when the humerus is fixed (flexed), and can aid in forced inspiration. The platysma is a large muscle layer that extends from its fascial insertions on the upper parts of the pectoralis major and deltoid muscles and rises medially through the collarbone to the side of the neck. The insertion sites include the symphysis, the lower border of the mandibular body, the lateral half of the lower lip, and the modiolus muscles near the buccal angle. The platysma wrinkles the skin at the nape of the neck obliquely. It can also help in the depression of the jaw, it helps to express horror and surprise, it is active in case of sudden deep inspiration, and it contracts noticeably in case of sudden and violent exertion.

Fascia of the Shoulder with a Direct

Relationship with the Rib Cage

The clavipectoral fascia, underneath the clavicular portion of the pectoralis major, fills in the gap between the pectoralis minor and subclavius muscles.  The fascial attachments include the following: the clavicle, by surrounding the subclavius muscle and blending with the deep cervical fascia that connects the omohyoid to the clavicle; the first rib and the fascia over the first two intercostal spaces; the coracoid process; and the axillary fascia. Special features of this fascia include the following: the costocoracoid membrane, which lies superior and medial to the pectoralis minor muscle; the costocoracoid ligament, with attachments from the coracoid process to the first rib; and the suspensory ligament of the

axilla, which lies inferior and lateral to the pectoralis minor muscle. The axillary fascia blends with the fascia of the serratus anterior muscle and the brachial fascia.  This fascia blends anteriorly with the pectoral and clavipectoral fascia; it blends posteriorly with the fascia of the scapula muscles

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