Biceps brachii muscle

The biceps brachii, commonly called the "biceps," is a prominent, fusiform muscle on the upper arm's anterior aspect. It plays a key role in forearm supination, elbow flexion, and shoulder stability. Its name reflects its two proximal heads: the long head and the short head.

Origin

• Long head: Originates from the supraglenoid tubercle of the scapula. Its tendon is extrasynovial within the shoulder joint and passes obliquely through the bicipital groove of the humerus before joining the short head.

• Short head: Originates from the coracoid process of the scapula.

Insertion

Both heads converge to form a single muscle belly in the central third of the upper arm. Distally, the biceps brachii inserts via a flattened tendon onto the radial tuberosity of the radius. Additionally, the bicipital aponeurosis, a broad fascial expansion, extends from the tendon of the biceps brachii and blends with the deep fascia of the medial forearm.

Innervation

The biceps brachii is innervated by the musculocutaneous nerve (C5-C7), a terminal branch of the lateral cord of the brachial plexus, that innervates all muscles in the anterior compartment of the arm.

Blood Supply

The muscle receives its arterial blood supply from the muscular branches of the brachial artery.

Functions

The biceps brachii is a multifunctional muscle:

• Supination: A powerful supinator of the forearm, especially when the elbow is flexed.

• Flexion: Assists in flexion of the elbow joint. However, the brachialis is the primary elbow flexor.

• Shoulder stability: The long head tendon contributes to passive stabilization of the shoulder joint.