Muscles of the upper limb

• The muscles of the upper extremity include those that attach the scapula to the thorax and generally move the scapula, those that attach the humerus to the scapula and generally move the arm, and those that are located in the arm or forearm that move the forearm, wrist, and hand.
• The muscles of the upper limb can be divided into 6 different regions: pectoral, shoulder, upper arm, anterior forearm, posterior forearm, and the hand.
• The pectoral region of the upper limb is located on the anterior chest wall and contains four muscles: the pectoralis major, pectoralis minor, serratus anterior, and subclavius.
• The pectoralis major is the most superficial muscle in the pectoral region, it is large and fan shaped, and is composed of a sternal head and a clavicular head.
• The distal attachment of both heads of the pectoralis major is into the intertubercular sulcus of the humerus.
• The clavicular head of the pectoralis major originates from the anterior surface of the medial clavicle.
• The sternocostal head of the pectoralis major originates from the anterior surface of the sternum, the superior six costal cartilages and the aponeurosis of the external oblique muscle.
• Palmaris Brevis is innervated by the ulnar nerve.
• Palmaris Brevis originates from the palmar aponeurosis and flexor retinaculum, attaches to the dermis of the skin on the medial margin of the hand.
• Adductor Pollicis is a large triangular muscle with two heads.
• The other head of Adductor Pollicis originates from the capitate and adjacent areas of metacarpals II and III.
• Adductor Pollicis is innervated by the ulnar nerve.
• Palmaris Brevis is a small, thin muscle, found very superficially in the subcutaneous tissue of the hypothenar eminence.
• Both heads of Adductor Pollicis attach into the base of the proximal phalanx of the thumb.
• Palmaris Brevis wrinkles the skin of the hypothenar eminence and deepens the curvature of the hand, improving grip.
• The radial artery passes anteriorly through the space between the two heads of Adductor Pollicis, forming the deep palmar arch.
• Adductor Pollicis is an adductor of the thumb.
• One head of Adductor Pollicis originates from metacarpal III.
• The function of the pectoralis major is to adduct and medially rotate the upper limb and draw the scapula anteroinferiorly.
• The clavicular head of the pectoralis major also acts individually to flex the upper limb.
• The pectoralis minor lies underneath its larger counterpart muscle, pectoralis major, both muscles form part of the anterior wall of the axilla region.
• The pectoralis minor originates from the 3rd-5th ribs and inserts into the coracoid process of the scapula.
• The function of the pectoralis minor is to stabilise the scapula by drawing it anteroinferiorly against the thoracic wall.
• The lateral epicondyle originates from the lateral epicondyle of the humerus and attaches to the posterior and lateral part of the olecranon, extending and stabilising the elbow joint and abducting the ulna during pronation of the forearm.
• The abductor pollicis longus is situated immediately distal to the supinator muscle in the hand, its tendon contributing to the lateral border of the anatomical snuffbox.
• The supinator has two heads of origin, one originating from the lateral epicondyle of the humerus and the other from the posterior surface of the ulna, and they insert together into the posterior surface of the radius.
• The extensor pollicis brevis can be found medially and deep to the abductor pollicis longus, its tendon contributing to the lateral border of the anatomical snuffbox in the hand.
• The abductor pollicis longus originates from the interosseous membrane and the adjacent posterior surfaces of the radius and ulna, and attaches to the lateral side of the base of metacarpal I, abducting the thumb.
• The extensor indicis proprius allows the index finger to be independent of the other fingers during extension.
• The supinator lies in the floor of the cubital fossa, has two heads, and its deep branch of the radial nerve passes between.
• The extensor pollicis brevis originates from the posterior surface of the radius and interosseous membrane, and attaches to the base of the proximal phalanx of the thumb, extending at the metacarpophalangeal and carpometacarpal joints of the thumb.
• The tendon of the extensor pollicis longus forms the medial border of the anatomical snuffbox in the hand.
• The extensor pollicis longus has a larger muscle belly than the EPB, its tendon travelling medially to the dorsal tubercle at the wrist, using the tubercle as a ‘pulley’ to increase the force exerted.
• Brachioradialis is a paradoxical muscle, with an origin and innervation characteristic of an extensor muscle, but it is actually a flexor at the elbow.
• The tendons of the ECRL and ECRB attach to metacarpal bones II and III.
• Extensor Digiti Minimi originates from the lateral epicondyle of the humerus, and attaches, with the extensor digitorum tendon, into the extensor hood of the little finger.
• Extensor Carpi Ulnaris is located on the medial aspect of the posterior forearm, and is able to produce adduction as well as extension at the wrist.
• Extensor Digiti Minimi is thought to originate from the extensor digitorum muscle, and in some people, these two muscles are fused together.
• Anconeus is situated medially and superiorly in the extensor compartment of the forearm, blended with the fibres of the triceps brachii, and the two muscles can be indistinguishable.
• Extensor Carpi Ulnaris originates from the lateral epicondyle of the humerus, and attaches to the base of metacarpal V.