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The biceps brachii muscle, or musculus biceps brachii in latin, is a muscle of the anterior upper arm. The word ‘biceps’ refers to its two heads, or origins, while brachii means ‘of the arm’. The short head of the biceps brachii muscle originates at the tip of the coracoid process of the scapula, where it blends with the origin of the coracobrachialis muscle. The long head of the biceps brachii muscle originates at the supraglenoid tubercle of the scapula, in an extrasynovial position within the intracapsular space of the glenohumeral joint, or shoulder joint. Note that the tendon of the long head of the biceps brachii moves laterally away from the supraglenoid tubercle to the humeral head where it then passes inferiorly, under the transverse humeral ligament, which extends from the lesser tubercle to the greater tubercle of the humerus, to travel along the intertubercular sulcus, or bicipital groove. The two heads of the biceps brachii muscle merge along the anterior aspect of the humerus. The muscle inserts onto the radial tuberosity of the radius, as well as the antebrachial, or deep fascia of the medial forearm through its distal membrane called the bicipital aponeurosis. Both heads of the biceps brachii muscle are innervated by the musculocutaneous nerve, and are vascularized by the brachial artery.
The long head of the biceps brachii is responsible for abduction of the arm from the trunk, while the short head of the biceps brachii is responsible for adduction. If the heads contract in unison flexion at the elbow joint occurs. When the forearm is flexed and pronated, the biceps brachii is the most powerful supinator of the forearm. The biceps brachii also helps to support the humeral head within the shoulder joint.
Between the biceps brachii muscle and the triceps brachii muscle of the posterior compartment of the arm, there are two grooves: the medial bicipital groove, and the lateral bicipital groove. The brachial artery, the median nerve, and the ulnar nerve can be found within the medial bicipital groove, while the radial nerve can be found within the lateral bicipital groove.
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