Shoulder 29. December. 2012 Thursday



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Supraspinatus & infraspinatus

The supraspinatus and infraspinatus muscles originate from two large fossae, one above and one below the spine, on the posterior surface of the scapula. They form tendons that insert on the greater tubercle of the humerus. The tendon of the supraspinatus inserts on the superior facet of the greater tubercle.

The tendon of the infraspinatus passes inserts on the middle facet of the greater tubercle.

The supraspinatus initiates abduction of the arm. The infraspinatus laterally rotates the humerus.



http://www.daviddarling.info/images/rotator_cuff.jpg



Teres minor and teres major

The teres minor muscle is a cord-like muscle that originates from a flattened area of the scapula immediately adjacent to its lateral border below the infraglenoid tubercle. Its tendon inserts on the inferior facet of the greater tubercle of the humerus. The teres minor laterally rotates the humerus and is a component of the rotator cuff.



The teres major muscle originates from a large oval region on the posterior surface of the inferior angle of the scapula. This broad cord-like muscle ends as a flat tendon that attaches to the medial lip of the intertubercular sulcus on the anterior surface of the humerus. The teres major medially rotates and extends the humerus.

http://ncpad.com/get/images/strengthexercisehandouts/INTrotation_TERES_MAJOR.jpg



Long head of triceps brachii




The long head of triceps brachii muscle originates from the infraglenoid tubercle and passes somewhat vertically down the arm to insert, with the medial and lateral heads of this muscle, on the olecranon of the ulna

The triceps brachii is the primary extensor of the forearm at the elbow joint. Because the long head crosses the glenohumeral joint, it can also extend and adduct the humerus.



ROTATOR CUFF MUSCLES

Four of the scapulohumeral muscles (intrinsic shoulder muscles)—supraspinatus, infraspinatus, teres minor, and subscapularis (referred to as the SITS muscles)—are called rotator cuff muscles because they form a musculotendinous rotator cuff around the glenohumeral joint. The rotator muscles are short muscles which covers and blends with all bu the inferior aspect of the shoulder joint. The supraspinatus, infraspinatus and teres minor are inserted from above down into the humeral greater tubercle, and the subscapularis is inserted into the lesser tubercle. All originate from scapula. All except the supraspinatus are rotators of the humerus; the supraspinatus, besides being part of the rotator cuff, initiates and assists the deltoid in the first 15° of abduction of the arm (See “Movements of the shoulder girdle” on page 7).



http://assets2.medhelp.org/adam/graphics/images/en/19622.jpg

The tendons of the SITS muscles blend with and reinforce the fibrous layer of the joint capsule of the glenohumeral joint, thus forming the rotator cuff that protects the joint and gives it stability. The tonic contraction of the contributing muscles holds the relatively large head of the humerus in the small, shallow glenoid cavity of the scapula during arm movements.

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