The action of lifting an arm can seem like a thoughtless movement, however, there is complex and intricate process that goes on within the human body to make that small movement happen. It involves bones, muscles, and nerves to complete this process, but it would not be able to start without a certain subconscious thought beforehand. Lateral abduction of the arm is defined as raising the humerus, radius, and ulna bones to ninety degrees, parallel to the ground, with the elbow extended, and wrist and fingers locked in place.
Lateral Abduction of the Arm
Extension of Humeroulnar and Radioulnar Joints
The bones involved in this movement are all the bones of the shoulder and arm, all of these bones are connected and without all of them working together they would not be able to complete this movement. The Pectoral Girdle, which is the basis of the shoulder joint, is connected to the axial skeleton by the sternoclavicular joint. It also holds the clavicle, which is connected to the axial skeleton, the scapula, which stabilizes the shoulder and the humerus together. However, the humerus is also connected to the scapula at the glenohumeral joint, which is a ball and socket joint, and allows the movement of the shoulder. The humerus is then connected to the humeroulnar and Radiohumeral joints, known as the elbow joint, where the trochlear notch fits into the olecranon fossa of the humerus. Moving farther down the arm, the ulna is connected to the humerus at the humeroulnar joint, and the radius right next to it is connected to the ulna at the proximal radioulnar joint. The biaxial joint, is the last part of the arm that works in lateral abduction, it is connected to the radius at the distal articular surface. The Intercarpal joints, between the proximal and distal row of carpals, are what help contribute to wrist movement.
Humerus (red), Scapula (blue), Clavicle (purple)
Though, the bones would not be able to move if it wasn’t for the muscles contracting and moving them into place. There are many different muscles that have to work together to make such a simple movement occur, the bones and muscles have to work together for it to be possible. Each muscle has an origin, insertion, and action. The origin is the anchor point of the muscle on the bone, whenever the origin is contracts, it pulls the muscle. The insertion point is at the opposite end of the origin, whenever a muscle contracts, the insertion point pulls the bone into place. Lastly the action of a muscle is simply what the muscle does in reference to the body. To be able to make the glenohumeral joint rotate and move into place, the deltoid, pectoralis major, and latissimuss dorsi are all responsible. The deltoid is the mover of the humerus during extension, its action is to abduct the arm—its origin is the lateral part of the clavicle and the spine of the scapula. The pectoralis major medially rotates the arm, its insertion points are the clavicular head of the clavicle, the sternocostal manubrium and sternum, and the six upper costal cartilages. The insertion point for this muscle is the bicipital groove of the humerus and the lip of the deltoid; the sternal and abdominal fibers are what extend to flex the joint of the shoulder. Lastly the latissimus dorsi is one of the most important, it extends the humerus. It does this by its insertion point at the bicipital groove on the humerus and its origin, which is located on the lumbar and sacral vertebrae of the spine.
The next group of muscles to work together includes the infraspinatus, supraspinatus, the teres major, and the subscapularis. These muscles form a rotator cuff around the head of the humerus and allow major movements of the joint to occur. To be able to move the radioulnar joint, the triceps brachii and anconeus muscles work closely together, the triceps are a principle extensor with the insertion point on the ulna, and the anconeus assists in the function...
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