Muscles of the Upper Limb Anterior Compartment

Muscles of the Anterior Compartment of the Upper Limb

• The anterior compartment of the arm is primarily responsible for elbow and shoulder flexion, and forearm supination.
• Key muscles: Biceps brachii, brachialis, brachioradialis.
• Biceps brachii: Two-headed muscle (short and long head) flexing the elbow, supinating the forearm, and contributing to shoulder flexion. Originates from the scapula and inserts on the radial tuberosity.
• Brachialis: Deep to biceps brachii, primarily flexing the elbow joint, particularly when the forearm is pronated. Originates from the distal humerus and inserts on the ulna.
• Brachioradialis: Involved in elbow flexion, most active in mid-range of movement with the forearm in neutral position (neither pronated nor supinated). Originates from the lateral supracondylar ridge of the humerus and inserts on the styloid process of the radius.

Muscles of the Posterior Compartment of the Upper Limb

• The posterior compartment is primarily responsible for elbow and shoulder extension, and various forearm actions including pronation.
• Key muscles: Triceps brachii, anconeus.
• Triceps brachii: Three-headed muscle (long, lateral, medial heads) extending the elbow, and contributing to shoulder extension (long head primary). Originates from the scapula and humerus and inserts on the olecranon process of the ulna.
• Anconeus: A small muscle assisting in elbow extension. Originates from the lateral epicondyle of the humerus and inserts on the lateral olecranon and posterior surface of the ulna.

Muscles of the Anterior Compartment of the Forearm

• The anterior forearm compartment is responsible for wrist and finger flexion, pronation, and wrist flexion.
• Key muscles: Flexor carpi radialis, flexor carpi ulnaris, palmaris longus, flexor digitorum superficialis, flexor pollicis longus, flexor digitorum profundus.
• Flexor carpi radialis: Flexes and abducts the wrist.
• Flexor carpi ulnaris: Flexes and adducts the wrist.
• Palmaris longus: Flexes the wrist, assists in flexing fingers (less important compared to other flexors).
• Flexor digitorum superficialis: Flexes the middle phalanges of the fingers.
• Flexor digitorum profundus: Flexes the distal phalanges of the fingers, crucial for fine motor skills.
• Flexor pollicis longus: Flexes the distal phalanx of the thumb, vital for thumb opposition and dexterity.

Muscles of the Posterior Compartment of the Forearm

• The posterior forearm compartment is responsible for wrist and finger extension.
• Key muscles: Extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, extensor pollicis longus, extensor pollicis brevis.
• Extensor carpi radialis longus: Extends and abducts the wrist.
• Extensor carpi radialis brevis: Extends and abducts the wrist.
• Extensor digitorum: Extends the fingers.
• Extensor digiti minimi: Extends the little finger.
• Extensor carpi ulnaris: Extends and adducts the wrist.
• Extensor pollicis longus: Extends the thumb.
• Extensor pollicis brevis: Extends the thumb.

Rotator Cuff Muscles

• The rotator cuff stabilizes the shoulder joint and enables smooth movement. Four muscles: supraspinatus, infraspinatus, teres minor, subscapularis.
• Supraspinatus: Essential for arm abduction.
• Infraspinatus: Aids in external (lateral) arm rotation.
• Teres minor: Assists in external (lateral) arm rotation.
• Subscapularis: The major internal (medial) arm rotator.

Other Important Muscles of the Upper Limb

• Deltoid: Triangular muscle abducting the arm.
• Pectoralis major: Fan-shaped muscle flexing, adducting, and medially rotating the arm.