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 different points of origin:
- 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 on the posterior surface of the humerus. An important anatomical landmark is that its site of origin lies strictly above the radial groove.
- Medial head (caput mediale): starts from the posterior surface of the humerus below the radial groove and extends all the way to the olecranon. Additionally, it originates from the intermuscular septa.
All three heads merge into a single, robust tendon that inserts into the olecranon of the ulna (olecranon ulnae). In this region, synovial bursae are located to protect the tendon: the subtendinous bursa (bursa subtendinea m. tricipitis brachii) and the subcutaneous olecranon bursa (bursa subcutanea olecrani). Within the substance of the tendon itself, an intratendinous bursa (bursa intratendinea olecrani) is frequently found.
Biomechanics: Acts as the main extensor of the forearm. Additionally, the long head extends and slightly adducts the arm, participating in its retropulsion. Blood supply: Deep brachial 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 radial collateral ligament (lig. collaterale radiale).
- Insertion: posterolateral surface of the ulna near the base of the olecranon.
Function: Acts as a weak assistant to the triceps in extending the forearm. Its specific task is to tense 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) and branches of the ulnar collaterals.
Articularis cubiti muscle (m. articularis cubiti)
Consists of small longitudinal muscle fibers. Sometimes they are 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, the muscle tenses the joint capsule, preventing it from being pinched between the articular surfaces. Innervation: Branches of the radial nerve. Blood supply: Branches of the articular vascular network of the elbow.
Important anatomical 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) are the most important pathways for the neurovascular bundles of the arm.
- Intertubercular groove serves as a natural canal for the passage of the tendon of the long head of the biceps.
- Cubital fossa is located at the level of the insertion of the biceps aponeurosis. This is a critically important site for palpating the brachial artery (a. brachialis) and performing intravenous punctures.
- Synovial bursae include the subdeltoid, subbicipital radial, and olecranon bursae (subcutaneous and subtendinous). When inflamed, they become primary sources of bursitis.
Interaction with the anterior group (antagonist muscles)
The posterior group (extensors) works in opposition to the anterior muscle group (flexors), which is 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) is the main flexor of the forearm, which also tenses the joint capsule anteriorly.
Briefly: answers to topical questions
In the formation of which topographic openings of the axillary fossa does the long head of the triceps brachii muscle participate?
The long head of the triceps brachii muscle divides the spaces on the posterior wall of the axilla, participating in the formation of two topographic openings.
- Trilateral space (foramen trilaterum) — the muscle forms its lateral border (the opening is located medially to the head itself).
- Quadrilateral space (foramen quadrilaterum) — the muscle forms its medial border (the opening is located laterally to the head itself).
What anatomical structures form the walls of the humeromuscular canal (radial nerve canal)?
The walls of the humeromuscular canal (radial nerve canal) are formed by the humerus and the heads of the triceps brachii muscle.
- Anterior wall (roof) — medial and lateral heads of the triceps brachii muscle (m. triceps brachii).
- Posterior wall (floor) — radial groove on the humerus (sulcus nervi radialis humeri).
What vessels and nerves pass through the humeromuscular canal?
The humeromuscular canal transmits a neurovascular bundle consisting of the radial nerve and the deep vessels of the arm.
- Radial nerve (n. radialis) — the largest branch of the brachial plexus.
- Deep brachial artery (a. profunda brachii) — a major branch of the brachial artery.
- Companion veins (vv. profundae brachii).
Which arteries participate in the formation of the arterial network of the elbow joint (rete articulare cubiti)?
The formation of the arterial network of the elbow joint (rete articulare cubiti) involves collateral and recurrent arteries that form an anastomotic system.
- Radial collateral artery (a. collateralis radialis) anastomoses with the radial recurrent artery (a. recurrens radialis).
- Middle collateral artery (a. collateralis media) anastomoses with the interosseous recurrent artery (a. interossea recurrens).
- Superior ulnar collateral artery (a. collateralis ulnaris superior) anastomoses with the posterior branch of the ulnar recurrent artery (r. posterior a. recurrens ulnaris).
- Inferior ulnar collateral artery (a. collateralis ulnaris inferior) anastomoses with the anterior branch of the ulnar recurrent artery (r. anterior a. recurrens ulnaris).
To remember how the triceps heads are positioned relative to the radial nerve groove, keep in mind: Lateral — Lies above (Higher), Medial — Smaller (Lower).
Class and exam questions
Which muscle is the primary extensor of the forearm?
The main extensor is the triceps brachii muscle (m. triceps brachii).
Where does the lateral head of the triceps originate?
It originates on the posterior surface of the humerus, strictly above the radial nerve groove.
What is the function of the articular muscle of the elbow?
It tenses the capsule of the elbow joint during movements to prevent it from being pinched.
Which nerve provides innervation to the posterior compartment of the arm?
The entire posterior group (triceps, anconeus, and articularis cubiti muscles) is innervated by the radial nerve (n. radialis).
What else to study on this topic
- Topography of the radial groove (radial nerve canal)
- Normal biomechanics of the elbow joint
- Syntopy of neurovascular bundles in the bicipital grooves
- Boundaries and contents of the cubital fossa
- Olecranon bursitis: clinical anatomy
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