Triceps Brachii Muscle (m. triceps brachii)
This is the largest muscle, covering almost the entire posterior surface of the humerus. True to its name, it has three separate heads with distinct origins:
- Long head (caput longum): originates from the infraglenoid tubercle of the scapula (tuberculum infraglenoidale). Its fibers descend, passing through the narrow space between the teres minor and teres major muscles.
- Lateral head (caput laterale): originates from the posterior surface of the humerus. A key topographical landmark is that its origin lies strictly superior to the radial nerve groove.
- Medial head (caput mediale): originates from the posterior surface of the humerus inferior to the radial nerve groove and extends down to the olecranon process. It additionally takes origin from the intermuscular septa.
All three heads merge into a common, powerful tendon that inserts into the olecranon process of the ulna (olecranon ulnae). Synovial bursae are located in this region to protect the tendon: the subtendinous bursa of the triceps brachii (bursa subtendinea m. tricipitis brachii) and the subcutaneous olecranon bursa (bursa subcutanea olecrani). An intratendinous bursa (bursa intratendinea olecrani) is frequently found within the substance of the tendon itself.
Biomechanics: Acts as the primary extensor of the forearm. Additionally, the long head extends and slightly adducts the arm, participating in its retroversion. Blood Supply: Profunda brachii artery (a. profunda brachii), posterior circumflex humeral artery (a. circumflexa humeri posterior), as well as superior and inferior ulnar collateral arteries.
Anconeus Muscle (m. anconeus)
A small muscle located in the elbow region.
- Origin: posterior surface of the lateral epicondyle of the humerus and the radial collateral ligament (lig. collaterale radiale).
- Insertion: posterolateral surface of the ulna near the base of the olecranon process.
Function: Acts as a weak assistant to the triceps in extending the forearm. Its specific task is to tataense the capsule of the elbow joint during movements. Innervation: Radial nerve (C7–C8). Blood Supply: Recurrent interosseous artery (a. interossea recurrens, a branch of the posterior interosseous artery) and branches of ulnar collaterals.
Articularis Cubiti Muscle (m. articularis cubiti)
Consists of small, longitudinal muscle bundles. They are sometimes described as separated fibers of the brachialis muscle (m. brachialis).
- Origin: anterior surface of the distal epiphysis of the humerus.
- Insertion: fibers directly blend into the anterior wall of the capsule of the elbow joint.
Function: During flexion and extension of the arm, this muscle tenses the articular capsule, preventing it from becoming pinched between the articular surfaces. Innervation: Branches of the radial nerve. Blood Supply: Branches of the periarticular vascular network of the elbow.
Important Topographical Landmarks
To understand the structure of the upper limb, it is necessary to know the key anatomical landmarks of this region:
- Bicipital grooves (medial and lateral) — serve as vital pathways for the neurovascular bundles of the arm.
- Intertubercular sulcus (bicipital groove) — serves as a natural channel for the tendon of the long head of the biceps.
- Cubital fossa — located at the level of insertion of the biceps aponeurosis. This is a critically important site for palpation of the brachial artery (a. brachialis) and for performing venipuncture.
- Synovial bursae — subdeltoid, subbicipital radial, and olecranon bursae (subcutaneous and subtendinous). When inflamed, they become primary sources of bursitis.
Interaction with the Anterior Compartment (Antagonist Muscles)
The posterior compartment (extensors) works in opposition to the anterior compartment (flexors), which are innervated by the musculocutaneous nerve (n. musculocutaneus):
- Biceps brachii muscle (m. biceps brachii) — provides flexion and supination of the forearm.
- Coracobrachialis muscle (m. coracobrachialis) — flexes and adducts the arm.
- Brachialis muscle (m. brachialis) — the primary flexor of the forearm, which also tenses the joint capsule anteriorly.