The biceps (Latin: musculus biceps brachii, “two-headed muscle of the arm”,often abbreviated to biceps brachii) is a big muscle that lays on the anterior of the upper arm in between the shoulder joint and the elbow joint. Both heads of the muscle emerge on the scapula and sign up with to create a single muscle which is connected to the upper forearm. While the biceps crosses both the shoulder and elbow joints, its primary purpose is at the elbow joint where it flexes the lower arm and supinates the lower arm. Both these motions are utilized when opening up a wine bottle with a corkscrew: initially biceps screws in the cork (supination), then it pulls out the cork out (flexion).
The biceps is among 3 muscles in the anterior compartment of the arm, together with the brachialis muscle and the coracobrachialis muscle, with which the biceps shares a nerve supply. The biceps muscle has 2 heads, the shortened head and the long head, differentiated according to their origin at the coracoid process and supraglenoid tubercle of the scapula, respectively. From its origin on the glenoid, the long head stays tendinous as it travels through the shoulder joint and through the intertubercular groove of the humerus. Extending from its origin on the coracoid, the tendon of the shortened head runs beside the tendon of the coracobrachialis as the conjoint tendon. In contrast to the other muscles in the anterior compartment of the arm, the biceps brachii muscle crosses 2 joints, the shoulder joint and the elbow joint.
Both heads of the biceps brachii participate in the middle arm to form a single muscle mass generally near the insertion of the deltoid to form a common muscle belly, although numerous structural research studies have actually shown that the muscle bellies stay unique structures without confluent fibers. As the muscle extends distally, the two heads turn 90 degrees externally prior to inserting onto the radial tuberosity. The shortened head inserts distally on the tuberosity while the long head inserts proximally nearer to the peak of the tuberosity. The bicipital aponeurosis, likewise called the lacertus fibrosus, is a thick fascial band that arranges near to the musculotendinous junction of the biceps brachii and radiates over and inserts onto the ulnar portion of the antebrachial fascia.
The tendon that connects to the radial tuberosity is partly or entirely surrounded by a bursa, the bicipitoradial bursa, which makes sure frictionless movement in between the biceps brachii tendon and the proximal radius throughout pronation and supination of the lower arm.
2 skeletal muscles lie beneath the biceps brachii. These are the coracobrachialis muscle, which like the biceps muscle connects to the coracoid process of the scapula, and the brachialis muscle which is connected to the ulna and along the mid-shaft of the humerus. Aside from those, the brachioradialis muscle is adjacent to the biceps and likewise inserts on the radius bone, though more distally.
The biceps muscle shares its nerve supply with the other 2 muscles of the anterior compartment. The skeletal muscles are supplied by the musculocutaneous nerve. Fibers of the 5th, 6th and seventh cervical nerves comprise the parts of the musculocutaneous nerve which supply the biceps.
The biceps brachii works across 3 joints. The most crucial of these actions is to supinate the lower arm and flex the elbow joint. Besides, the long head of biceps avoids the upward displacement of the head of the humerus. In more detail, the actions are, by joint:
- Proximal radioulnar joint of the elbow: The biceps brachii function as an effective supinator of the lower arm, i.e. it turns the palm upwards. This action, which is assisted by the supinator muscle, needs the humeroulnar joint of the elbow to be a minimum of partly flexed. If the humeroulnar joint, is totally extended, supination is then mainly performed by the supinator muscle. The biceps is an especially effective supinator of the lower arm due to the distal accessory of the muscle at the radial tuberosity, on the opposite side of the bone from the supinator muscle. When flexed, the biceps efficiently pulls the radius back into its neutral supinated position in concert with the supinator muscle.
- Humeroulnar joint of the elbow: The biceps brachii likewise operates as an essential flexor of the lower arm, especially when the lower arm is supinated. Functionally, this action is carried out when raising an item, such as a bag of groceries or when carrying out a biceps curl. When the lower arm remains in pronation (the palm deals with the ground), the brachialis, brachioradialis, and supinator function to flex the lower arm, with very little contribution from the biceps brachii. It is likewise crucial to keep in mind that no matter lower arm position, (supinated, pronated, or neutral) the force applied by the biceps brachii stays the very same; nevertheless, the brachioradialis has a much higher modification in effort depending upon position than the biceps throughout concentric contractions. That is, the biceps can just apply a lot force, and as lower arm position modifications, other muscles need to compensate.
- Glenohumeral joint (shoulder joint): Numerous weaker functions take place at the glenohumeral joint. The biceps brachii weakly helps in forward flexion of the shoulder joint (bringing the arm forward and up-wards). It might likewise add to abduction (bringing the arm out to the side) when the arm is externally (or laterally) turned. The shortened head of the biceps brachii likewise helps with horizontal adduction (bringing the arm throughout the body) when the arm is internally (or medially) turned. Lastly, the shortened head of the biceps brachii, due to its accessory to the scapula (or shoulder blade), helps with stabilization of the shoulder joint when a heavy weight is brought in the arm. The tendon of the long head of the biceps likewise helps in holding the head of the humerus in the glenoid cavity.