Triceps brachii muscle
Anatomy and supply
The triceps brachii (triceps) is a large, three-headed muscle of the upper arm.
- long head: originates at the infraglenoid tubercle of the scapula. From there it courses between the teres major and teres minor and divides the axillary space into two halves.
- medial head: has its' origin at the dorsal humerus distally from the radial sulcus. Its' fibers are connected with the medial intermuscular septum.
- lateral head: originates at the dorsal humerus proximally from the radial sulcus where it is fixed to the lateral intermuscular septum.
All three heads together form a thick tendon which inserts at the olecranon of the ulna and additionally to the capsule of the elbow joint and antebrachial fascia. Under the triceps tendon lies an important bursa preventing excessive friction of the tendon with the olecranon (subtendinous bursa of triceps brachii).
The radial nerve (C6-C8), which supplies the triceps, is in close relationship with the muscle. First it runs within the radial sulcus of humerus where it is covered by both the medial and lateral triceps head. From there it courses to the crook of the arm along the lateral bicipital groove between the triceps and biceps.
Due to its' superficial course, the triceps determines the contour of the dorsal upper arm. The proximal part of the triceps is partly covered by the deltoid. Both the lateral and long heads can be easily palpated, whereas the medial head lies more deeply, as it is overlaid by the other two.
The triceps is the most important extensor muscle of the elbow. Hereby the medial head is the most active of all three. Its' antagonists (particularly the biceps and brachialis) are physiologically more powerful than the triceps, which is why we have a slight bend at the elbow when our arms are freely hanging during rest. Furthermore, the long triceps head also crosses the shoulder joint making it the only two-jointed triceps part. During contraction it pulls the upper arm towards the trunk (adduction) and behind (retroversion). The distal fibers of the triceps fulfill another task, namely the protection of the capsule of the elbow joint during extreme extending movements.