Dominic Stone
The biceps brachii, commonly known as the biceps, is a large, thick muscle on the front of the upper arm. The biceps brachii is a two-joint muscle, with two heads that originate on the scapula and join to form a single muscle belly, which is attached to the forearm. The muscle's name, which means two-headed muscle of the arm in Latin, reflects its structure. The biceps brachii is one of the chief muscles of the arm and plays a role in several arm movements.
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What You'll Learn
The biceps brachii is a two-headed muscle
The biceps brachii, commonly known as the biceps, is a large, thick muscle on the front of the upper arm between the shoulder and the elbow. It is one of the chief muscles of the arm and is composed of two heads, which is where it gets its name from. The short head, or "caput breve", is located on the medial side and originates from the coracoid process of the scapula. The long head, or "caput longum", is located on the lateral side and originates from the supraglenoid tubercle of the scapula.
The two heads of the biceps brachii unite to form a single muscle belly, which is attached to the upper forearm. The biceps brachii is a two-joint muscle, acting on both the shoulder joint and the elbow joint. In the shoulder joint, the long head pulls the arm away from the trunk (abduction) and turns it inwards (inward rotation), while the short head pulls the arm back towards the trunk (adduction). When both heads contract simultaneously, it leads to a bend in the arm (flexion).
In the elbow joint, the muscle bends the forearm (flexion) and rotates it outwards (supination). This supination is most powerful when the elbow is flexed. The biceps brachii is a particularly powerful supinator of the forearm due to its distal attachment at the radial tuberosity, on the opposite side of the bone from the supinator muscle. The biceps' main function is at the elbow, where it flexes and supinates the forearm. Both these movements are used when opening a bottle with a corkscrew: first, the biceps screw in the cork (supination), then it pulls the cork out (flexion).
The biceps brachii is supplied by the musculocutaneous nerve (C5-C7), a branch of the brachial plexus. The arterial supply to the biceps brachii varies, coming from up to eight vessels originating from the brachial artery in the middle third of the arm.
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It acts on the shoulder and elbow joints
The biceps brachii is a large, thick muscle on the upper arm. It is a two-joint muscle, acting on both the shoulder and elbow joints. The biceps brachii has two heads, a short head and a long head, which unite to form a single muscle belly. The long head originates from the supraglenoid cavity of the scapula, while the short head originates from the coracoid process of the scapula.
In the shoulder joint, the two heads of the biceps brachii partially enforce opposite movements. The long head pulls the arm away from the trunk (abduction) and turns it inwards (inward rotation). On the other hand, the short head pulls the arm back towards the trunk (adduction). When both heads contract simultaneously, it leads to an arm bend (flexion). The biceps also have the important task of supporting the humeral head within the shoulder joint.
In the elbow joint, the biceps brachii bends the forearm (flexion) and rotates it outwards (supination). This supination is most powerful when the elbow is flexed. The biceps brachii is a powerful supinator of the forearm, turning the palm upwards. This movement is similar to using a corkscrew to open a bottle.
The brachialis muscle lies underneath the biceps brachii and is the prime mover of elbow flexion, generating about 50% more power than the biceps. It originates from the anterior surface of the distal half of the humerus and inserts onto the tuberosity of the ulna.
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The biceps is a forearm flexor
The biceps brachii, commonly known as the biceps, is a large, thick muscle on the front of the upper arm. It is one of the chief muscles of the arm, and its name derives from its two heads, which merge into one unique distal body. The biceps is a forearm flexor, and it is involved in several movements of the arm.
The biceps brachii works across three joints: the glenohumeral, elbow, and radio-ulnar joints. It originates in two places: the coracoid process, a protrusion of the scapula (shoulder blade), and the upper glenoid cavity, the hollow for the shoulder joint. Both heads of the muscle arise on the scapula and join to form a single muscle belly, which is attached to the upper forearm. The tendon of this muscle attaches to the radial tuberosity, a bone of the forearm.
The biceps brachii bends the forearm toward the upper arm, allowing for lifting and pulling movements. This flexion of the forearm is one of the main functions of the biceps. Additionally, the biceps supinate the forearm, turning the palm forward or upward. This supination action, along with flexion, was first described by Leonardo da Vinci in a series of annotated drawings made between 1505 and 1510. However, this function remained undiscovered by the medical community until it was re-discovered by William Cheselden in 1713.
The biceps brachii is not the only muscle involved in forearm flexion. The brachialis muscle, which lies beneath the biceps, is the prime mover of elbow flexion, generating about 50% more power than the biceps. The brachialis, brachioradialis, and supinator muscles also function to flex the forearm when it is in pronation (palm facing the ground), with minimal contribution from the biceps. The force exerted by the biceps remains the same regardless of forearm position, but other muscles must compensate as forearm position changes.
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The brachialis muscle lies beneath the biceps brachii
The biceps brachii muscle is a large, thick muscle of the arm, composed of two heads: a short head and a long head. The long head is located on the lateral side, while the short head is on the medial side. The biceps brachii is one of the chief muscles of the arm, acting on both the shoulder and elbow joints. It is involved in abduction, adduction, and flexion of the arm, as well as inward rotation and supination of the forearm.
The brachialis muscle, or brachialis anticus, is located deep to the biceps brachii, underneath it in the upper arm. This position makes it unobservable without removing or dissecting the biceps brachii muscle. The brachialis originates from the anterior surface of the distal half of the humerus and inserts onto the tuberosity of the ulna. It is innervated by the musculocutaneous nerve and may also receive additional innervation from the radial nerve.
While the biceps brachii is a more visible and well-known muscle, the brachialis plays a crucial role in providing additional strength and power during movements. During a bicep curl, for example, the biceps brachii is the most active muscle initially, but the brachialis works underneath, providing extra strength to lift the weight. Similarly, in a pull-up exercise, both muscles work together to aid in lifting the body upwards.
The primary function of the brachialis is to flex the forearm at the elbow joint, acting as a synergist to the biceps brachii. It is the prime mover of elbow flexion, generating about 50% more power than the biceps. The brachialis, by virtue of its deep position, exerts greater force during elbow flexion, highlighting the complexity of muscle interactions and their roles in movement.
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The biceps brachii is supplied by the musculocutaneous nerve
The biceps brachii is a large, thick muscle on the upper arm, composed of a short head and a long head. The muscle is responsible for generating movements in the glenohumeral, elbow, and radio-ulnar joints. The biceps brachii is supplied by the musculocutaneous nerve, a branch of the brachial plexus. The musculocutaneous nerve carries fibres of cervical spinal nerves five through seven (C5-C7). It leaves the axilla and descends into the coracobrachialis muscle fibres, passing through the axillary artery.
The musculocutaneous nerve innervates the muscles of the anterior compartment of the arm, including the biceps brachii, brachialis, and coracobrachialis. It provides motor innervation to the biceps brachii and brachialis muscles, facilitating movements such as flexion and supination (outward rotation) of the forearm. The nerve follows a unique course between the biceps brachii and brachialis muscles, not paralleling any specific artery.
The arterial supply to the biceps brachii muscle can vary, receiving blood from up to eight vessels originating from the brachial artery in the middle third of the arm. The musculocutaneous nerve also supplies the lateral cutaneous nerve of the forearm, providing sensory innervation to the lateral forearm. This nerve branch supplies the sensation to the lateral side of the forearm from the elbow to the wrist.
The biceps brachii muscle plays a crucial role in supporting the humeral head within the shoulder joint. In the shoulder joint, the long head of the muscle pulls the arm away from the trunk (abduction) and turns it inwards (inward rotation), while the short head pulls the arm back towards the trunk (adduction). When both heads contract simultaneously, it leads to an arm bend (flexion).
Injuries to the musculocutaneous nerve can occur through overuse of the coracobrachialis, biceps, and brachialis muscles, leading to stretching or compression of the nerve. Symptoms of such injuries include pain, tingling, or reduced sensation over the lateral side of the forearm.
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Frequently asked questions
The biceps brachii muscle, commonly known as the biceps, is a large, thick muscle on the front of the upper arm. It is one of the chief muscles of the arm and has two heads.
The biceps brachii is located between the shoulder and elbow joints. It is one of four muscles in the upper arm, with three in the anterior compartment (biceps brachii, brachialis, coracobrachialis) and one in the posterior compartment (triceps brachii).
The biceps brachii works across three joints: the glenohumeral, elbow, and radio-ulnar joints. Its main function is to supinate the forearm and flex the elbow. It also has an important role in supporting the humeral head within the shoulder joint.
The biceps brachii gets its name from its two heads, which merge into one muscle belly. The long head originates from the supraglenoid tubercle of the scapula, while the short head originates from the coracoid process of the scapula.
