Muscles of the Arm and HandPSK 4U

MR. S. KELLY

NORTH GRENVILLE DHS

Biceps BrachiiOrigin: scapula

Insertion: radius, fascia of forearm (bicipital aponeurosis)

Action: supination and elbow flexion

Innervation: musculocutaneous

BrachialisOrigin: humerus

Insertion: ulna

Action: elbow flexion (assists biceps brachii by instigating this movement)

Lies deep to biceps brachii

Innervation: musculocutaneous, radial

Triceps Brachii (long, medial, and lateral heads)

Origin: scapula and posterior humerus

Insertion: proximal posterior ulna

Action: elbow extension; shoulder extension and adduction (when elbow is extended)

Innervation: axillary, radial

Forearm Muscles: acting on elbow, wrist, and finger joints

FLEXOR-PRONATORS

Originate via a common flexor tendon from medial epicondyle of humerus (common flexor origin)

EXTENSOR-SUPINATORS

Originates via common extensor tendon from lateral epicondyle of humerus (common extensor origin)

More on the Forearm3 layers of muscles: deep, intermediate, and superficial

A layer of fascia separates deep layer of muscles from intermediate and superficial

Flexor retinaculum, aka transverse carpal ligament: roof of the carpal tunnel

Flexor tendons and median nerve pass through the carpal tunnel

FR increases effectiveness of tendons by preventing bowstringing, changing direction of forces when necessary

SupinatorOrigin: lateral epicondyle of humerus, ulna, radial collateral ligament

Insertion: proximal 1/3 of radius

Action: prime mover in supination of forearm (aided by biceps brachii)

PronatorsPRONATOR QUADRATUS

Origin: distal anterior ulna

Insertion: distal anterior radius

Action: prime mover in pronation of the forearm (assisted by pronator teres)

Innervation: median

PRONATOR TERES

Origin: common flexor tendon, proximal ulna

Insertion: lateral radius

Action: pronation of forearm, weak elbow flexor

Innervation: median

Pronators

Flexor Digitorum ProfundusOrigin: ulna, interosseus membrane

Insertion: phalanges, after penetrating tendons of FDS

Action: flexes fingers 1-4

Innervation: anterior interosseus, ulnar

Flexor Policis LongusOrigin: radius, interosseus membrane

Insertion: distal phalanx of thumb

Action: thumb flexion

FPL is unique to humans: not present (or does very little) in other primates

Flexor Digitorum SuperficialisOrigin: ulnar collateral ligament of elbow, CFO

Insertion: intermediate phalanges of 4 fingers

Action: flexes PIP, MP, wrist joints

Innervation: median

Palmaris LongusAbsent in about 14% of population

Absence does not affect grip strength

Disadvantage: absence means lack of popular source for tendon graft

Test: touch pads of thumb and 5th

finger + flex wrist… 2 or 3 tendons?

BrachioradialisOrigin: lateral humerus

Insertion: styloid process of radius

Action: a flexor that also works to pronate AND supinate (in supination, it pronates as it flexes, and vice versa)

Innervation: median

Abductor Policis LongusOrigin: ulna, radius, interosseus membrane

Insertion: 1st metacarpal, trapezium, abductor policis brevis tendon

Action: abduction of thumb, keeps trapezium stable with APB

Innervation: radial

Extensor DigitorumOriginates on lateral epicondyle

Inserts on medial 4 digits

Extends phalanges and wrist joint

Insertion splits on 4 digits to medial and lateral sides.

Anatomical Snuff BoxExtensor policis longus tendon (posterior border)

Anterior (lateral) border: extensor policis brevis and abductor policislongus

Skeletal components: scaphoid and trapezium

Importance: blood supply of scaphoid is retrograde, therefore proximal fractures require attention to prevent necrosis

Name: comes from the practice of placing powdered tobacco on this surface for sniffing. Don’t ask why… almost sounds as stupid as vaping, no?

Significance (other than arcane tobacco practices): pain and tenderness in this area are often indicative of scaphoid or other carpal fractures.

Anatomical Snuff Box borders

Primary Hand Grip Muscles (identification only)