Muscles of the Upper Limb PDF

# Muscles of the Upper Limb ## Introduction This document describes the various muscles of the upper limb: * **Muscles of the Shoulder** * **Scapular muscles** * **Muscles Acting on the Shoulder Joint** (Scapulohumeral muscles) * **Muscles of the Arm** * **Anterior Compartment** *...

# Muscles of the Upper Limb ## Introduction This document describes the various muscles of the upper limb: * **Muscles of the Shoulder** * **Scapular muscles** * **Muscles Acting on the Shoulder Joint** (Scapulohumeral muscles) * **Muscles of the Arm** * **Anterior Compartment** * **Posterior Compartment** * **Muscles of the Forearm** * **Anterior Compartment** * **Posterior Compartment** * **Muscles of the Hand** * **Thenar** * **Hypothenar** * **Adductor compartment** * **Short Muscles** * **Dorsal interossei** * **Palmar interossei** ## Muscles of the Shoulder ### Scapular Muscles * **Trapezius** * **Proximal attachment:** * Lateral third of superior nuchal line * External occipital protuberance * Nuchal ligament * Spinous processes of C7-T12 vertebrae * **Distal attachment:** * Lateral third of clavicle * Acromion * Spine of scapula * **Innervation:** Spinal Accessory (CN XI) (motor fibers) and spinal nerves (C3 and C4) (pain and proprioception) * **Muscle action:** * **Descending part:** Elevates * **Ascending part:** Depresses * **Middle part:** Retracts * **Descending and ascending parts:** Act together to rotate glenoid cavity superiorly * **Latissimus Dorsi** * **Proximal attachment:** * Spinous processes of inferior 6 thoracic vertebrae * Thoracolumbar fascia * Iliac crest. * Inferior 3 or 4 ribs * **Distal attachment:** Floor of intertubercular sulcus of humerus * **Innervation:** Thoracodorsal nerve (C6, C7, C8) * **Muscles action:** * Extends * Adducts * Medially rotates humerus * Raises body toward arms during climbing * **Levator Scapulae** * **Proximal attachment:** Posterior tubercles of transverse processes of C1-C4 vertebrae * **Distal attachment:** Medial border of scapula superior to root of scapular spine * **Innervation:** Dorsal scapular (C4, C5) and cervical (C3, C4) nerves * **Muscle action:** * Elevates scapula * Rotates its glenoid cavity inferiorly by rotating scapula * **Rhomboid Minor and Major:** * **Proximal attachment:** * **Minor:** Nuchal ligament, spinous processes of C7 and T1 vertebrae. * **Major:** Spinous processes of T2-T5 vertebrae * **Distal attachment:** * **Minor:** Smooth triangular area at medial end of scapular spine * **Major:** Medial border of scapula from level of spine to inferior angle * **Innervation:** * **Minor:** Dorsal scapular nerve (C4, C5) * **Major:** Dorsal scapular nerve (C4, C5) * **Muscle action:** * **Rhomboid minor and major:** Retract scapula and rotate its glenoid cavity inferiorly; fix scapula to thoracic wall ### Muscles Acting on the Shoulder Joint * **Supraspinatus** * **Proximal attachment:** Supraspinous fossa of scapula * **Distal attachment:** Superior facet of greater tubercle of humerus * **Innervation:** Suprascapular nerve (C4, C5, C6) * **Muscle action:** * Initiates * Assists deltoid in abduction of arm * Acts with the other rotator cuff muscles * **Infraspinatus** * **Proximal attachment:** Infraspinous fossa of scapula * **Distal attachment:** Middle facet of greater tubercle of humerus * **Innervation:** Suprascapular nerve (C5, C6) * **Muscle action:** * Laterally rotates arm * Acts with the other rotator cuff muscles * **Teres Minor** * **Proximal attachment:** Middle part of lateral border of scapula * **Distal attachment:** Inferior facet of greater tubercle of humerus * **Innervation:** Axillary nerve (C5, C6) * **Muscle action:** * Laterally rotates arm * Acts with the other rotator cuff muscles * **Teres Major** * **Proximal attachment:** Posterior surface of inferior angle of scapula * **Distal attachment:** Medial lip of intertubercular sulcus of humerus * **Innervation:** Lower Subscapular nerve (C5, C6) * **Muscle action:** * Adducts * Medially rotates arm * **Subscapularis** * **Proximal attachment:** Subscapular fossa (most of anterior surface of scapula) * **Distal attachment:** Lesser tubercle of humerus * **Innervation:** Upper and lower Subscapular nerves (C5, C6, C7) * **Muscle action:** * Medially rotates arm * As part of rotator cuff, helps hold head of humerus in glenoid cavity ## Muscles of the Arm ### Anterior Compartment * **Biceps Brachii** * **Proximal attachment:** * **Short head:** Tip of coracoid process of scapula * **Long head:** Supraglenoid tubercle of scapula * **Distal attachment:** Tuberosity of radius and fascia of forearm via bicipital aponeruosis * **Innervation:** Musculocutaneous nerve (C5, C6, C7) * **Muscle action:** * Supinates forearm * When it is supine, flexes forearm * Short head resists dislocation of shoulder * **Coracobrachialis** * **Proximal attachment:** Tip of coracoid process of scapula * **Distal attachment:** Middle third of medial surface of humerus * **Innervation:** Musculocutaneous nerve (C5, C6) * **Muscle action:** * Helps flex and adduct arm * Resists dislocation of shoulder * **Brachialis** * **Proximal attachment:** Distal half of anterior surface of humerus, superior to radial groove * **Distal attachment:** Coronoid process and tuberosity of ulna * **Innervation:** Musculocutaneous nerve (C5, C6) * **Muscle action:** Flexes forearm in all positions * **Triceps Brachii** * **Proximal attachment:** * **Long head:** Infraglenoid tubercle of scapula * **Lateral head:** Posterior surface of humerus, superior to radial groove * **Medial head:** Posterior surface of humerus, inferior to radial groove * **Distal attachment:** Olecranon of ulna and fascia of forearm * **Innervation:** Radial nerve (C6, C7, C8) * **Muscle action:** * Chief extensor of forearm * Long head resists dislocation of humerus; especially important during adduction ### Posterior Compartment * **Triceps Brachii** (described above) ## Muscles of the Forearm ### Anterior Compartment * **Superficial layer:** * **Pronator Teres** * **Ulnar head:** Medial epicondyle of humerus (common flexor origin) * **Humeral head:** Coronoid process * **Distal attachment:** Middle of convexity of lateral surface of radius * **Innervation:** Median nerve (C6, C7) * **Muscle action:** Pronates and flexes forearm (at elbow). * **Flexor Carpi Radialis (FCR)** * **Proximal attachment:** Medial epicondyle of humerus (common flexor origin) * **Distal attachment:** Base of 2nd metacarpal * **Innervation:** Median nerve (C7, C8) * **Muscle action:** Flexes and abducts hand (at wrist). * **Palmaris Longus:** * **Proximal attachment:** Medial epicondyle of humerus (common flexor origin) * **Distal attachment:** Distal half of flexor retinaculum and apex of palmar aponeurosis * **Innervation:** Median nerve (C7, C8) * **Muscle action:** Flexes hand (at wrist) and tenses palmar aponeurosis. * **Flexor Carpi Ulnaris (FCU)** * **Humeral head:** Medial epicondyle of humerus (common flexor origin) * **Ulnar head:** Olecranon and posterior border of ulna (via aponeurosis) * **Distal attachment:** Pisiform, hook of hamate, 5th metacarpal * **Innervation:** Ulnar nerve (C7, C8) * **Muscle action:** Flexes and adducts hand (at wrist). * **Intermediate layer:** * **Flexor Digitorum Superficialis (FDS)** * **Humero-ulnar head:** Medial epicondyle (common flexor origin) and coronoid process. * **Radial head:** Middle of anterior surface of radius * **Distal attachment:** Shafts of middle phalanges of medial four digits * **Innervation:** Median nerve (C7, C8, T1) * **Muscle action:** Flexes middle phalanges at proximal interphalangeal joints of middle four digits; acting more strongly, it also flexes proximal phalanges at metacarpophalangeal joints. * **Deep layer:** * **Flexor Digitorum Profundus (FDP)** * **Medial part:** Superior half of anterior border of ulna and interosseous membrane * **Lateral part:** Proximal three quarters of medial and anterior surfaces of ulna and interosseous membrane. * **Distal attachment:** Bases of distal phalanges of 4th and 5th digits * **Innervation:** Ulnar nerve (C8, T1) * **Muscle action:** Flexes distal phalanges 4 and 5 at distal interphalangeal joints. * **Flexor Pollicis Longus (FPL)** * **Proximal attachment:** Anterior surface of radius and adjacent interosseous membrane * **Distal attachment:** Base of distal phalanx of thumb * **Innervation:** Anterior interosseous nerve, from median nerve (C8, T1) * **Muscle action:** Flexes distal phalanges 2 and 3 at distal interphalangeal joints. * **Pronator Quadratus** * **Proximal attachment:** Distal quarter of anterior surface of ulna. * **Distal attachment:** Distal quarter of anterior surface of radius * **Innervation:** None. * **Muscle action:** Pronates forearm, and its deep fibers bind radius and ulna together. * **Outcropping muscles of deep layer:** * **Abductor Pollicis Longus (APL)** * **Proximal attachment:** Posterior surface of proximal halves of ulna, radius, and interosseous membrane * **Distal attachment:** Base of 1st metacarpal * **Innervation:** Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve * **Muscle action:** Abducts thumb and extends it at carpometacarpal joint * **Extensor Pollicis Longus (EPL)** * **Proximal attachment:** Posterior surface of middle third of ulna and interosseous membrane * **Distal attachment:** Dorsal aspect of base of distal phalanx of thumb * **Innervation:** Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve * **Muscle action:** Extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints. * **Extensor Pollicis Brevis (EPB)** * **Proximal attachment:** Posterior surface of distal third of radius and interosseous membrane * **Distal attachment:** Dorsal aspect of base of proximal phalanx of thumb * **Innervation:** Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve * **Muscle action:** Extends proximal phalanx of thumb at metacarpophalangeal joint. ### Posterior Compartment * **Superficial layer:** * **Brachioradialis:** * **Proximal attachment:** Proximal two thirds of lateral supraepicondylar ridge of humerus * **Distal attachment:** Lateral surface of distal end of radius, proximal to styloid process * **Innervation:** Radial nerve (C5, C6, C7) * **Muscle action:** Relatively weak flexion of forearm; maximal when forearm is in midpronated position. * **Extensor Carpi Radialis Longus (ECRL):** * **Proximal attachment:** Lateral sup epicondylar ridge of humerus * **Distal attachment:** Dorsal aspect of base of 2nd metacarpal * **Innervation:** Radial nerve (C6, C7) * **Muscle action:** Extends and abducts hand at the wrist joint; ECRL active during fist clenching. * **Extensor Carpi Radialis Brevis (ECRB):** * **Proximal attachment:** Lateral epicondyle of humerus (common extensor origin) * **Distal attachment:** Dorsal aspect of base of 3rd metacarpal * **Innervation:** Deep branch of radial nerve (C7, C8) * **Muscle action:** Extends medial four digits primarily at metacarpophalangeal joints, secondarily at interphalangeal joints. * **Extensor Digitorum:** * **Proximal attachment:** Lateral epicondyle of humerus; posterior border of ulna via a shared aponeurosis * **Distal attachment:** Extensor expansions of medial four digits * **Innervation:** Deep branch of radial nerve (C7, C8) * **Muscle action:** Extends 5th digit primarily at metacarpophalangeal joint, secondarily at interphalangeal joint. * **Extensor Digiti Minimi (EDM):** * **Proximal attachment:** Lateral epicondyle of humerus; radial collateral and anular ligaments; supinator fossa; crest of ulna * **Distal attachment:** Extensor expansion of 5th digit * **Innervation:** Deep branch of radial nerve (C7, C8) * **Muscle action:** Extends and adducts hand at wrist joint (also active during fist clenching). * **Extensor Carpi Ulnaris (ECU):** * **Proximal attachment:** Lateral epicondyle of humerus; radial collateral and anular ligaments; supinator fossa; crest of ulna * **Distal attachment:** Dorsal aspect of base of 5th metacarpal * **Innervation:** Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve * **Muscle action:** Supinates forearm; rotates radius to turn palm anteriorly or superiorly (if elbow is flexed). * **Deep layer:** * **Supinator:** * **Proximal attachment:** Lateral, posterior, and anterior surfaces of proximal third of radius * **Distal attachment:** Extensor expansion of 2nd digit. * **Innervation:** Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve * **Muscle action:** Extends 2nd digit (enabling its independent extension); helps extend hand at wrist. * **Extensor Indicis:** * **Proximal attachment:** Posterior surface of distal third of ulna and interosseous membrane * **Distal attachment:** Extensor expansion of 2nd digit * **Innervation:** Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve * **Muscle action:** Supinates forearm; rotates radius to turn palm anteriorly or superiorly (if elbow is flexed). ## Muscles Of The Hand ### Thenar Muscles * **Opponens Pollicis:** * **Proximal attachment:** Tubercles of scaphoid and trapezium * **Distal attachment:** Lateral side of 1st metacarpal * **Innervation:** Recurrent branch of median nerve (C8, T1) * **Muscle action:** To oppose thumb, it draws 1st metacarpal medially to center of palm and rotates it medially. * **Abductor Pollicis Brevis:** * **Proximal attachment:** Lateral side of base of proximal phalanx of thumb * **Distal attachment:** Lateral side of base of proximal phalanx of thumb * **Innervation:** Recurrent branch of median nerve (C8, T1) * **Muscle action:** Abducts thumb, it helps oppose it. * **Flexor Pollicis Brevis:** * **Proximal attachment:** Tubercles of scaphoid and trapezium * **Distal attachment:** Medial side of base of proximal phalanx of thumb * **Innervation:** Recurrent branch of median nerve (C8, T1) * **Muscle action:** Flexes thumb. ### Hypothenar Muscle * **Abductor Digiti Minimi:** * **Proximal attachment:** Pisiform * **Distal attachment:** Medial side of base of proximal phalanx of 5th digit * **Innervation:** Deep branch of ulnar nerve (C8, T1) * **Muscle action:** Abducts 5th digit; assists in flexion of its proximal phalanx. * **Flexor Digiti Minimi Brevis:** * **Proximal attachment:** Hook of hamate and flexor retinaculum * **Distal attachment:** Medial border of 5th metacarpal * **Innervation:** Deep branch of ulnar nerve (C8, T1) * **Muscle action:** Flexes proximal phalanx of 5th digit. * **Opponens Digiti Minimi:** * **Proximal attachment:** Hook of hamate * **Distal attachment:** Medial border of 5th metacarpal * **Innervation:** Deep branch of ulnar nerve (C8, T1) * **Muscle action:** Draws 5th metacarpal anterior and rotates it, bringing 5th digit into opposition with thumb. ### Adductor Compartment * **Adductor Pollicis:** * **Oblique head:** Bases of 2nd and 3rd metacarpals, capitate, and adjacent carpals * **Transverse head:** Anterior surface of shaft of 3rd metacarpal * **Distal attachment:** Medial side of base of proximal phalanx of thumb * **Innervation:** Deep branch of ulnar nerve (C8, T1) * **Muscle action:** Adducts thumb toward lateral border of palm. ### Short Muscles: * **Lumbricals:** * **1st and 2nd:** Lateral two tendons of flexor digitorum profundus (as unipennate muscles) * **3rd and 4th:** Medial three tendons of flexor digitorum profundus (as bipennate muscles) * **Distal attachment:** Lateral sides of extensor expansions of 2nd-5th digits * **Innervation:** * **1st and 2nd:** Median Nerve (C8, T1) * **3rd and 4th:** Deep branch of ulnar nerve (C8, T1) * **Muscle action:** Flex metacarpophalangeal joints; extend interphalangeal joints of 2nd-5th digits. * **Dorsal Interossei (1st-4th):** * **Proximal attachment:** Adjacent sides of two metacarpals (as bipennate muscles) * **Distal attachment:** Bases of proximal phalanges; extensor expansions of 2nd-4th digits * **Innervation:** Deep branch of ulnar nerve (C8, T1) * **Muscle action:** Abduct 2nd-4th digits from axial line; act with lumbricals in flexing metacarpophalangeal joints and extending interphalangeal joints. * **Palmar Interossei (1st-3rd):** * **Proximal attachment:** Palmar surfaces of 2nd, 4th, and 5th metacarpals (as unipennate muscles) * **Distal attachment:** Bases of proximal phalanges; extensor expansions of 2nd, 4th, and 5th digits * **Innervation:** Deep branch of ulnar nerve (C8, T1) * **Muscle action:** Adduct 2nd, 4th, and 5th digits toward axial line; assist lumbricals in flexing metacarpophalangeal joints and extending interphalangeal joints.