Biceps brachii
Biceps brachii muscle (m. biceps brachii) is a powerful flexor and supinator of the forearm. As the name implies, it has two heads originating on the scapula.
- The long head originates from the supraglenoid tubercle (tuberculum supraglenoidale) of the scapula. Its tendon courses inferiorly within the intertubercular sulcus of the humerus.
- The short head originates from the apex of the coracoid process (processus coracoideus).
Both heads merge and insert via a tendon into the radial tuberosity (tuberositas radii). An important structure is the bicipital aponeurosis (aponeurosis m. bicipitis brachii), which branches off the main tendon and blends into the antebrachial fascia (medially, towards the cubital fossa).
Functions: in addition to powerful forearm flexion and supination, the long head participates in flexion and weak abduction of the shoulder, and also stabilizes the humeral head. The short head assists in shoulder adduction.
Topography and blood supply: the medial and lateral bicipital grooves (sulcus bicipitalis medialis et lateralis) run along the sides of the muscle belly. The bicipitoradial bursa (bursa bicipitoradialis) is located in the area of muscle insertion. Blood supply is provided by branches of the brachial artery (a. brachialis), including the radial recurrent artery (a. recurrens radialis), as well as the superior and inferior ulnar collateral arteries (aa. collaterales ulnaris superior et inferior).
Coracobrachialis
Coracobrachialis muscle (m. coracobrachialis) is located in the upper part of the arm. It originates from the apex of the coracoid process of the scapula (processus coracoideus) by a common tendon with the short head of the biceps.
The muscle runs inferiorly and inserts into the medial surface of the humerus at its middle third (along the linea brachii medialis).
Functions: the muscle flexes and adducts the arm, and also plays an important role in stabilizing the humeral head.
Features: the musculocutaneous nerve (n. musculocutaneus, segments C5–C7), which innervates the entire anterior compartment, often perforates the coracobrachialis muscle specifically. Blood supply is provided by the anterior and posterior circumflex humeral arteries (aa. circumflexae humeri anterior et posterior).
Brachialis
Brachialis muscle (m. brachialis) lies deeper than the biceps muscle and is the primary flexor of the forearm at the elbow joint.
It originates from the anterior surface of the distal (lower) half of the humerus, as well as from the medial and lateral intermuscular septa of the arm. The muscle inserts into the ulnar tuberosity (tuberositas ulnae) and coronoid process (processus coronoideus).
Clinical significance: some muscle fibers of the brachialis blend directly into the anterior wall of the elbow joint capsule. This is an important protective mechanism that shields the joint capsule from impingement during flexion.
Innervation and blood supply: like the other muscles of this group, it is innervated by the musculocutaneous nerve (n. musculocutaneus, C5–C7). However, the lateral part of the muscle often receives additional branches from the radial nerve (n. radialis). Blood is supplied by branches of the brachial artery (a. brachialis), collateral ulnar arteries (aa. collaterales ulnaris sup./inf.), and the radial recurrent artery (a. recurrens radialis).
Briefly: answers to topical questions
Which vessels and nerves run through the medial bicipital groove of the arm?
The medial bicipital groove contains:
- medial cutaneous nerve of the arm (n. cutaneus brachii medialis);
- medial cutaneous nerve of the forearm (n. cutaneus antebrachii medialis).
The basilic vein (v. basilica) runs along the medial surface of the arm; in the lower third of the arm, it pierces the deep fascia and goes deep.
What function does the bicipital aponeurosis (Pirogov's aponeurosis) perform in relation to the neurovascular bundle?
The bicipital aponeurosis (aponeurosis m. bicipitis brachii, or lacertus fibrosus) runs medially and blends into the antebrachial fascia, separating superficial veins from deep neurovascular structures.
What terminal sensory branch does the musculocutaneous nerve give off in the forearm?
The musculocutaneous nerve continues into the forearm as the lateral cutaneous nerve of the forearm (n. cutaneus antebrachii lateralis), which innervates the skin of the lateral part of the forearm.
General rule of innervation for the anterior compartment: all three muscles receive branches from the musculocutaneous nerve (n. musculocutaneus).
Class and exam questions
Which muscle is the main flexor of the forearm?
The primary flexor of the forearm at the elbow joint is the brachialis muscle (m. brachialis), and not the biceps, as is often mistakenly thought.
What structure is associated with the common origin of the short head of the biceps and the coracobrachialis muscle?
Both of these muscles originate via a common tendon from the apex of the coracoid process of the scapula (processus coracoideus).
Which nerve pierces the coracobrachialis muscle?
It is frequently perforated by the musculocutaneous nerve (n. musculocutaneus), which then proceeds to the rest of the muscles in the anterior compartment.
How does the brachialis muscle protect the elbow joint?
Part of its fibers blend directly into the anterior wall of the elbow joint capsule, pulling it taut during contraction and preventing impingement.
What else to study on this topic
- Topography of the bicipital grooves (sulcus bicipitalis medialis et lateralis) and the neurovascular bundles passing through them.
- Structure and functions of the bicipital aponeurosis (aponeurosis m. bicipitis brachii).
- Features of the dual innervation of the lateral part of the brachialis muscle.
- Topography and clinical significance of the bicipitoradial bursa (bursa bicipitoradialis).
- Blood supply to the anterior compartment: anastomoses of collateral and recurrent arteries in the elbow region.
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