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Biceps muscle

Synonyms: two-headed upper arm muscle, arm flector, biceps
German: Musculus biceps brachii

1 Definition

The biceps muscle is a two-headed and two-articulated muscle tha belongs to the muscles of the upper arm. The heads of the muscle are called "Caput longum" and "Caput breve".

2 Anatomy

2.1 Origin

The origin of the long head (Caput longum) is the supraglenoid tubercle of the scapula. Whereas, the short head (Caput breve) has a sinewy origin in the coracoid process of the scapula (raven beak process).

2.2 Insertion

The sinewy insertion of the biceps muscle is the radial tuberosity of the radius and - via the bicipital aponeurosis, also called lacertus fibrosus - the antebrachial fascia. Thus, the biceps muscle passes over 2 joints, the shoulder and the elbow joint.

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2.3 Particularities

The muscle is covered by the deltoid muscle in its course, so that you can only recognize the division when removing this muscle during preparation. The origin tendon of the longer biceps head (Caput longum) passes through the interbubercular groove of the humerus on its way to the supraglenoid tubercle, and after that, through the joint capsule of the shoulder joint to its origin on the supraglenoid tubercle of the scapula - surrounded by the intertubercular sheath.

2.4 Varieties

In app. 10% of the cases, an additional Caput tertium can originate from humerus and join the muscle curvature.

3 Innervation

The innervation of the biceps muscle is provided by the musculocutaneous nerve from the brachial plexus (segments: C5-C6 or C7).

4 Function

Together with the brachialis muscle, the biceps muscle is responsible for the flexion of the forearm in the elbow joint. Moreover, it is the strongest supinator in the elbow flexed at a right angle. Its supinator effect increases with increasing flexion. It is the direct antagonist of the triceps muscle.

In the shoulder joint, contraction of the Caput longum causes a slight abduction movement of the arm, as well as a slight internal rotation, while the contraction of the Caput breve causes a slight adduction. Contraction of both heads results in an anteversion of the arm. Furthermore, it spans the antebrachial fascia via its insertion in the bicipital aponeurosis.

5 Clinical presentation

The neurological examination of the biceps muscle innervation is done by testing the biceps tendon reflex. Especially in elderly people or due to excessive strain, traumatic ruptures of the tendon can occur, the so-called biceps tendon rupture.

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