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Interactive Shoulder Part 2 Muscle Structure By Primal Pictures EDITOR’S NOTE: The following is a small sample of the Interactive Shoulder CD in the ground breaking Primal Pictures 3-D Anatomy CD ROM series DELTOIDS Proximal Attachments The deltoid is a thick, powerful muscle which covers the shoulder joint and upper humerus ( Slide 1, Slide 2). It arises from the anterior border of lateral third of clavicle, the lateral border of acromion and the lower lip of scapular spine, as well as from the fascia over infraspinatus muscle. Distal Attachments It inserts on the V shaped deltoid tuberosity half way down the lateral aspect of the shaft of humerus. Nerve Supply Deltoid is innervated by the axillary nerve (C 5 ,6). Actions It is a powerful abductor of the humerus. Abduction is, however, initiated by supraspinatus. The anterior portion of deltoid contributes to flexion of the humerus ( Movie 1, Movie 2), with the posterior portion to extension ( Movie 1, Movie 2). When supraspinatus is torn, the upward pull of deltoid results in superior subluxation of the humeral head. The acromial part of the deltoid is multipennate. Tendinous septa arising from the acromion and the deltoid tuberosity interdigitate, with short muscle fibers extending between the septa. This gives the muscle a short but powerful pull. LATISSIMUS DORSI Latissimus dorsi is a large flat muscle which passes between trunk and humerus, acting on both the shoulder joint and shoulder girdle. Proximal Attachments It arises from spines and supraspinous ligaments of the lower six thoracic vertebrae deep to trapezius, and from thoracolumbar fascia, by which it is attached to the spines of all lumbar and sacral vertebrae. In addition, it arises from posterior iliac crest and the lower three or four ribs. It passes upwards and laterally, gaining a small slip from the inferior angle of scapula. Distal Attachment The muscle converges to form a flat 'strap like' tendon, which winds around the inferior border of teres major to reach its humeral attachment in the floor of the intertubercular groove of the humerus. The lower border of the tendon unites with the tendon of teres major for a short distance. A bursa lies between the two. Nerve Supply The thoracodorsal nerve (C 6 , 7 ,8). Actions Latissimus dorsi retracts the shoulder girdle, and is a powerful extensor of the flexed humerus (for example, climbing). It also adducts and internally rotates the humerus. It is an accessory muscle of respiration, particularly violent expiration. Latissimus dorsi and teres major form the posterior fold of the axilla. TRAPEZIUS The trapezius is a broad flat triangular muscle which lies superficially at the back of neck and upper trunk, the pair forming the 'trapezium' from which it derives its name. Proximal Attachments It arises from the superior nuchal line of occipital bone, the external occipital protuberance, ligamentum nuchae, the spines of seventh cervical and all thoracic vertebrae and the intervening supraspinous ligaments. Distal Attachments The upper fibers pass down and laterally to insert in the posterior aspect of lateral clavicle. The middle fibers pass horizontally to the medial border of acromion and upper lip of scapula spine. The lower fibers ascend to the tubercle of scapula spine. The upper fibers form the posterior border of the posterior triangle of the neck. Nerve Supply Trapezius receives motor innervation from the spinal accessory nerve, which enters from the posterior triangle. Fibers from the ventral rami of C3 and C4 are thought to be sensory. Actions The upper fibers elevate the scapula, ( Slide 1, Slide 2 ) for example when carrying a weight. The middle fibers produce bracing of the shoulder girdle. The lower fibers depress the medial aspect of the scapula and shoulder, for example using the hands to rise from sitting. The action of upper and lower fibers together tend to rotate the scapula so that the glenoid fossa points upwards and forwards. CLICK HERE for more information on the Primal Pictures 3-D Anatomy series and for details on exclusive PTontheNET.com member discounts Disclaimer No warranty is given as to the accuracy of the information on any of the pages in this website. No responsibility is accepted for any loss or damage suffered as a result of the use of that information or reliance on it. It is a matter for users to satisfy themselves as to their or their client’s medical and physical condition to adopt the information or recommendations made. Notwithstanding a users medical or physical condition, no responsibility or liability is accepted for any loss or damage suffered by any person as a result of adopting the information or recommendations. © Copyright Personal Training on the Net 1998 2003 All rights reserved