Anatomy of Arm Muscles

The muscles of the arm are divided into two main compartments:

1. Anterior (flexor) compartment – primarily responsible for flexion of the elbow and supination of the forearm.

2. Posterior (extensor) compartment – primarily responsible for extension of the elbow and wrist.

1. Anterior Compartment of Arm

Biceps Brachii

Origin:

Long head: supraglenoid tubercle of scapula

Short head: coracoid process of scapula

Insertion: radial tuberosity and bicipital aponeurosis

Action: flexes elbow, supinates forearm, weak shoulder flexion

Nerve: musculocutaneous nerve

Brachialis

Origin: distal half of anterior humerus

Insertion: coronoid process and tuberosity of ulna

Action: flexes elbow (primary flexor)

Nerve: musculocutaneous nerve

Coracobrachialis

Origin: coracoid process of scapula

Insertion: medial surface of humerus

Action: flexes and adducts arm at shoulder

Nerve: musculocutaneous nerve

2. Posterior Compartment of Arm

Triceps Brachii

Origin:

Long head: infraglenoid tubercle of scapula

Lateral head: posterior humerus above radial groove

Medial head: posterior humerus below radial groove

Insertion: olecranon process of ulna

Action: extends elbow; long head assists in shoulder extension and adduction

Nerve: radial nerve

Anconeus

Origin: lateral epicondyle of humerus

Insertion: lateral aspect of olecranon and proximal ulna

Action: assists triceps in elbow extension; stabilizes elbow joint

Nerve: radial nerve

3. Key Functions of Arm Muscles

Flexion of elbow: biceps brachii, brachialis, brachioradialis

Extension of elbow: triceps brachii, anconeus

Supination of forearm: biceps brachii

Shoulder flexion and adduction: coracobrachialis and long head of biceps