How To Remember Every Muscle in the Upper Limb and Arm | Corporis

This section introduces muscles originating on the spine that control arm movement. Key muscles include the Trapezius (looks like a trapezoid, has upper, middle, and lower parts) and Latissimus Dorsi (widest muscle, 'lats', lateral and dorsal). Deeper muscles include the Rhomboid Major and Minor (retract shoulder blades, maintain posture, rhomboid major is rhomboid-shaped, minor is cylindrical) and Levator Scapulae (elevates scapula).

This part focuses on chest muscles. The Pectoralis Major is the large, superficial chest muscle, while the Pectoralis Minor is smaller and lies underneath. The Serratus Anterior has a jagged, serrated appearance. Intercostal muscles are located between the ribs.

This section covers muscles moving the glenohumeral joint. The Deltoid is the biggest and most superficial, shaped like a Greek delta. Underneath are the four rotator cuff muscles (SITS): Supraspinatus (superior to scapular spine), Infraspinatus (inferior to scapular spine), Teres Minor (forms an 'M' with the humerus), and Subscapularis (underneath the scapula). The Teres Major, a major arm mover, is distinguished by its lower origin on the scapula and humerus, giving it more leverage than the Teres Minor.

This segment explains upper arm muscles using Latin names. Key muscles are the Biceps Brachii (two-headed), Triceps Brachii (three-headed), Coracobrachialis (attaches coracoid process to upper arm), Brachioradialis (connects humerus to radius), and Brachialis (stubbiest elbow flexor). The Anconeus is a small accessory muscle on the back that extends the elbow.

The anterior forearm muscles are primarily flexors. Examples include the Flexor Carpi Radialis (flexes hand on radial side), Flexor Carpi Ulnaris (flexes hand on ulnar side), Palmaris Longus (small muscle, long tendon, some people lack it), Pronator Teres (pronates arm, Pivots hand down), and Pronator Quadratus (square-shaped, pronates). Other flexors are the Flexor Digitorum Superficialis (flexes fingers at proximal interphalangeal joint) and Flexor Digitorum Profundus (deep finger flexor). The Flexor Pollicis Longus is a long muscle that bends the thumb.

The posterior forearm muscles are mainly extensors. These include the Extensor Carpi Ulnaris (extends wrist on ulnar side), Extensor Carpi Radialis Longus and Brevis (extends wrist on radial side), Extensor Digitorum (extends fingers), and Extensor Digiti Minimi (extends the pinky finger). Deeper muscles include the Extensor Indicis (extends index finger) and muscles creating the 'anatomical snuff box' for thumb abduction and extension: Abductor Pollicis Longus, Extensor Pollicis Longus, and Extensor Pollicis Brevis. The Supinator muscle is found at the elbow and performs supination.

This final section covers hand muscles. The Thenar Mass consists of four thumb-moving muscles: Flexor Pollicis Brevis (flexes thumb), Opponens Pollicis (opposition of thumb), Adductor Pollicis (adducts thumb), and Abductor Pollicis Brevis (abducts thumb). The Hypothenar Mass moves the pinky finger: Opponens Digiti Minimi (opposes pinky), Flexor Digiti Minimi Brevis (flexes pinky), and Abductor Digiti Minimi (abducts pinky). The Palmaris Brevis pulls on connective tissue for grip. Lastly, the Lumbricals flex the metacarpophalangeal joints and extend interphalangeal joints, and the Interossei muscles (Palmar and Dorsal) adduct and abduct the fingers, respectively.