Shoulder muscles Flashcards
What are the deltoids?
The deltoids are fleshy triangle shaped muscles that form the rounded shape of your shoulders. They are the powerful abductors of the humerus. The origin of each deltoid winds across the shoulder girdle from the spine of the scapula to the clavicle. It inserts into the proximal humerus.
What is the latissimus dorsi?
This is the large flat muscle, which covers the lower and middle back. It originates on the lower spine and ilium and then sweeps superiorly to the proximal end of the humerus. The latissimus dorsi extends and adducts the humerus. These are very important during power strokes as when swimming or striking a blow.
What is the pectoralis major?
It is the large fan shaped muscle of the chest that converges to a flat tendon. It adducts and flexes the arm.
What are the infraspinatus and teres minor?
They seem to act as one. In addition to the outward rotary action they also do an important job of holding the head of the humerus in the glenoid fossa, which prevents dislocation of the shoulder when abducted. Origin at the scapula insertion humerus.
What is the teres major?
It works with the latissimus dorsi in downward and backward movement of the humerus and also in inward rotation.
What is the subscapularis?
Chief action is medial rotation and also contributes to stabilisation of the gleno humeral joint.
What is the suprapinatus?
The supraspinatus muscle leads to abduction of the arm at the shoulder joint. It is the main agonist muscle for this movement during the first 15 degrees of its arc. Beyond this point, the deltoid muscle becomes more effective in abduction. It surrounds and encloses the shoulder. It helps to resist the inferior gravitational forces placed across the shoulder joint due to the downward pull from the weight of the upper limb.
