The long head of biceps brachii is one of the two heads of biceps brachii, a muscle at the front of the upper arm, between the shoulder and elbow. The other is the short head; these are distinct portions with separate upper attachments. Together, they bend the elbow and turn the forearm so that the palm faces upwards when the elbow is bent.
Where is biceps brachii located?
Within the muscular system, biceps brachii belongs to the anterior compartment of the arm: the group of muscles at the front of the arm enclosed by connective tissue. It lies beneath the skin and superficial connective tissue, forming much of the visible contour of the front of the arm.
Brachialis, another elbow-flexing muscle, lies deep to biceps brachii against the humerus, the arm bone. Coracobrachialis, a muscle that acts at the shoulder, lies towards the inner side of its upper part.
Near the elbow, the biceps tendon enters the cubital fossa, the hollow at the front of the joint. Here, the brachial artery lies on the inner side of the tendon, with the median nerve farther inward.
What are the long and short heads?
The long head of biceps brachii and the short head begin separately at the shoulder. A head is a portion of a muscle distinguished by its attachment at the origin, usually the less mobile attachment during an action. In the arm, the long head generally lies towards the outer side and the short head towards the inner side.
Their fleshy portions come together to form the main muscle belly, the thick, contractile part of the muscle. They share a lower attachment through the biceps tendon, a strong cord of connective tissue that transmits muscular force to bone.
Where does biceps brachii originate?
Both heads originate from the scapula, or shoulder blade, but at different sites.
- The long head arises from the supraglenoid tubercle, a prominence above the scapula’s shoulder socket, and the superior part of the glenoid labrum. The labrum is a rim of fibrocartilage, a tough supporting tissue, around that socket.
- The short head arises from the tip of the coracoid process, a forward-projecting part of the scapula. It shares this attachment region with coracobrachialis.
The long head tendon crosses the shoulder joint within its fibrous capsule, the connective-tissue sleeve enclosing the joint. Although it lies inside the capsule, it remains outside the synovial cavity, the fluid-containing space between the joint surfaces.
It then enters the intertubercular groove, a channel between prominences on the upper humerus, before continuing into the arm. The short head does not follow this route through the shoulder joint.
Where does biceps brachii insert?
The insertion, usually the more mobile attachment, is mainly on the radial tuberosity. This is a rough prominence near the upper end of the radius, the forearm bone on the thumb side. The common biceps tendon passes through the front of the elbow to reach it.
A second attachment is provided by the bicipital aponeurosis, a broad, flat sheet of tendon spreading from the lower muscle and tendon towards the inner side of the forearm. It blends with the deep fascia, the strong connective-tissue covering around the forearm muscles.
The bicipital aponeurosis passes in front of the brachial artery and median nerve. Because the main tendon attaches to the radius rather than the ulna, the other forearm bone, biceps can rotate the radius as well as bend the elbow.
What does biceps brachii do?
The main actions are flexion of the elbow and supination of the forearm. Flexion means bending a joint; supination is rotation that turns the palm forwards when the arm hangs by the side, or upwards when the elbow is bent. Biceps also assists flexion of the arm at the shoulder joint, bringing the arm forwards.
| Action | Movement produced | Anatomical basis |
|---|---|---|
| Elbow flexion | Bends the elbow | The tendon crosses the front of the elbow joint |
| Forearm supination | Turns the palm forwards or upwards | Pull on the radius rotates it relative to the ulna |
| Shoulder flexion | Helps bring the arm forwards | Both heads cross the shoulder region |
Biceps is particularly effective as a supinator when the elbow is flexed. Its contribution to elbow flexion also varies with forearm position, being stronger when the forearm is supinated than when the palm is turned downwards.
Brachialis also flexes the elbow, but its attachment to the ulna means it does not produce forearm supination. This distinction explains why biceps has a combined bending and rotating role.
What are its nerve and blood supplies?
Motor fibres of the nervous system, which carry signals for muscle contraction, reach biceps brachii through the musculocutaneous nerve. Its supply comes principally from spinal nerve roots C5 and C6, the nerve connections associated with those cervical, or neck, spinal levels.
The musculocutaneous nerve descends between biceps brachii and brachialis after passing through coracobrachialis. It supplies branches to both heads of biceps.
Blood reaches the muscle mainly through muscular branches of the brachial artery. This artery runs along the inner side of the arm before entering the cubital fossa.
How can you locate biceps brachii in the 3D model?
The atlas entry beside this article is anchored to the long head of biceps brachii, one part of the whole muscle rather than another name for it. Its side-specific structures are the long head of left biceps brachii and the long head of right biceps brachii.
In the 3D model, rotate the arm to view its front, then select and isolate the long head. Zoom and rotate to examine its position, and fade it to compare the space it occupies with neighbouring structures. Keep the distinction between the selected head and the whole biceps brachii in mind when relating the model to the attachments and actions described here.