The coracobrachialis muscle is a muscle in the upper medial part of the arm. It is located within the anterior compartment of the arm. It originates from the coracoid process of the scapula; it inserts onto the middle of the medial aspect of the body of the humerus. It is innervated by the musculocutaneous nerve. It acts to adduct and flex the arm. Structure Origin Coracobrachialis muscle arises from the apex of the coracoid process of the scapula, in common with the short head of the biceps brachii, and from the intermuscular septum between the two muscles. It the smallest of the three muscles that attach to the coracoid process (the other being the pectoralis minor, and the short head of the biceps brachii). Insertion It is inserted (by means of a flat tendon) into an impression at the middle of the medial surface and border of the body of the humerus (shaft of the humerus) between the origins of the triceps brachii and brachialis. Innervation Coracobrachialis muscle is perforated by and innervated by the musculocutaneous nerve, which arises from the anterior division of the upper trunk (C5, C6) and middle trunk (C7) of the brachial plexus. Function The action of the coracobrachialis is to flex and adduct the arm at the glenohumeral joint (shoulder joint). Also, the coracobrachialis resists deviation of the arm from the frontal plane during abduction. Therefore, the contraction of the coracobrachialis leads to two distinct movements at the shoulder joint. It both draws the humerus forward, causing flexion of the arm, and draws the humerus toward the torso, causing adduction of the arm. To a smaller extent, it also turns the humerus inwards, causing internal rotation. Another important function of the coracobrachialis is the stabilization of the humeral head within the shoulder joint, especially when the arm is hanging freely at a person's side. Clinical significance The overuse of the coracobrachialis can lead to stiffening of the muscle. Common causes of injury include chest workouts or activities that require one to press the arm very tight towards the body, e.g. work on the rings in gymnastics. Symptoms of overuse or injury are pain in the arm and shoulder, radiating down to the back of the hand. In more severe cases, the musculocutaneous nerve can get trapped, causing disturbances in sensation to the skin on the radial part of the forearm and weakened flexion of the