The musculus biceps brachii, also known as the biceps, is an important muscle on the front of your upper arm. It has two heads, which is also reflected in its name: “bi” means “two-”, “ceps” means “heads” and “brachii” comes from “brachium” or “brachion”, which means arm or upper arm. The name of the muscle comes mostly from Latin, except for “brachion”, which comes from Greek (1). But enough about the name, let’s take a closer look at the biceps! In this article, you will learn everything about the origins, insertions, functions, and peculiarities of this fascinating muscle.

Musculus biceps brachii – Origin, insertion, and innervation

The musculus biceps brachii runs over two joints: the shoulder joint and the elbow joint. The two heads of the biceps originate at different places on your scapula. The short head, also called caput breve, originates from the coracoid process, a small bony projection on the front of your scapula. The long head, also called caput longum, originates from the supraglenoid tubercle, a small elevation on the upper edge of the socket of your shoulder joint (1, 2, 3).

The nerve that innervates the muscle is the N. musculocutaneus (C5–C6). It originates from the lateral bundle of the brachial plexus, which contains nerve fibers from the fifth and sixth cervical vertebrae (3). The musculus biceps brachii is the key muscle for the spinal cord segment C6, as it is mainly innervated by this segment. This means that the nerve fibers that control this muscle exit from the sixth cervical vertebra (2).

The long head of the biceps originates from the shoulder joint capsule and passes through the joint cavity. It exits the capsule through the intertubercular groove, a groove between two bony projections on the humerus. It helps to stabilize the shoulder joint by keeping the humeral head in the socket. Both heads of the biceps join and attach to the radius. More specifically, to the radial tuberosity, a rough area on the inner side of the bone. Besides the attachment to the radial tuberosity, the biceps brachii also extends into the bicipital aponeurosis, a wide tendon sheet that merges with the superficial muscle layer of the forearm, the antebrachial fascia. This aponeurosis serves as an insertion site for numerous muscles (1, 2, 3).

Musculus biceps brachii – Functions

The biceps brachii has a significant effect on the elbow joint due to its attachment to the forearm. It is probably the most important flexor of the elbow joint. The muscle is also the strongest supinator of the forearm, especially when the elbow joint is bent. Its tendon wraps around the radius. When it contracts, the tendon rolls off like a yo-yo and rotates the radius around its long axis. When the elbow joint is straightened, the biceps brachii cannot exert much supination force, because the pull direction of the biceps runs mostly parallel to the pronation-supination axis (1, 2, 3).

Since the biceps brachii muscle also crosses the shoulder joint, it also moves the upper arm in the shoulder joint. In the shoulder joint, it can abduct** (long head), adduct** (short head), and bring the upper arm into anteversion** (1, 2, 3). According to the lever arm, the musculus biceps brachii is only slightly involved in the corresponding joint movements in the shoulder. It helps with other muscles, mainly in the stabilization of the humeral head in the socket (2).

As you can see, the biceps is a very versatile muscle that is involved in many movements of your arm. It is not only responsible for the strength and shape of your upper arm but also for the mobility and stability of your shoulder and elbow joints. I hope you enjoyed this article and learned something new about the musculus biceps brachii. If you want to learn more about the anatomy and function of the muscles, feel free to check out other articles on my blog, such as the anatomy of the Adductors. I appreciate your feedback and questions in the comments. You may also find interesting videos on fitness & co on my YouTube channel.

*Flexion means that the angle between the upper and lower arm becomes smaller. Supination means that the palm is turned upwards (1,2).

**Abduction means that the arm is moved away from the body. Adduction means that the arm is moved towards the body. Anteversion means that the arm is lifted forward (1, 2).

References

1. Sobotta, J. (2017). Sobotta, Atlas der Anatomie Band 1: Allgemeine Anatomie und Bewegungsapparat. Deutschland: Urban & Fischer in Elsevier.

2. Waschke, J., Böckers, T. M., & Paulsen, F. (Eds.). (2019). Sobotta Lehrbuch Anatomie. Elsevier Health Sciences.

3. Palastanga, N., & Soames, R. (2014). Anatomie und menschliche Bewegung: Strukturen und Funktionen. Elsevier, Urban&FischerVerlag.