Lecture Notes on Human Musculature

Muscles of the Scapula and Thoracic Region

• Serratus Anterior     * Origin: External surface of Ribs $1-8$ or $9$.     * Insertion: Scapula (anterior surface of medial border).     * Innervation: $C5-C7$ Long Thoracic Nerve.     * Action: Scapular abduction (ABD) and upward rotation (ROT); Depress the scapula and hold the medial border against the rib cage.

• Upper Trapezius     * Origin: Occiput (external protuberance and medial $1/3$ of superior nuchal line); Ligamentum nuchae; $C7$ (spinous process).     * Insertion: Clavicle (posterior, lateral $1/3$), Acromion, and spine of Scapula.     * Innervation: Accessory $XI$ and ventral ramus $C3,4$.     * Action (Bilateral): Extend the head and neck.     * Action (Unilateral): Laterally flex to the same side; Rotate to the opposite side; Elevate the scapula; Upwardly rotate the scapula.

• Middle Trapezius     * Origin: $T1-T5$ (spinous process); Supraspinous ligaments.     * Insertion: Clavicle (posterior, lateral $1/3$), Acromion, and spine of Scapula.     * Innervation: Accessory $XI$ and ventral ramus $C3,4$.     * Action: Scapular adduction (ADD); Stabilize the scapula.

• Lower Trapezius     * Origin: $T6-T12$ (spinous process); Supraspinous ligaments.     * Insertion: Clavicle (posterior, lateral $1/3$), Acromion, and spine of Scapula.     * Innervation: Accessory $XI$ and ventral ramus $C3,4$.     * Action: Scapular ADD, depression, and upward ROT.

• Levator Scapulae     * Origin: $C1-C4$ (transverse processes).     * Insertion: Scapula (medial border between superior angle and superior portion of scapular spine).     * Innervation: $C3-C4$; $C5$ dorsal scapular nerve.     * Action (Unilateral): Scapular elevation; Downward ROT; Lateral flexion and ROT of the cervical spine to the same side.     * Action (Bilateral): Cervical spine extension (EXT).

• Rhomboid Major     * Origin: $T2-T5$ (spinous process).     * Insertion: Scapula (medial border between spine and inferior angle).     * Innervation: $C5$ Dorsal Scapular.     * Action: Scapular ADD, downward ROT, and elevation.

• Rhomboid Minor     * Origin: $C7-T1$ (spinous process).     * Insertion: Scapula (upper portion of medial border from spine of scapula).     * Innervation: $C5$ Dorsal Scapular.     * Action: Scapular ADD, elevation, and downward ROT.

Muscles of the Shoulder and Upper Arm

• Latissimus Dorsi     * Origin: Inferior angle of scapula, spinous processes of last $6$ thoracic vertebrae, last $3$ or $4$ ribs, thoracolumbar fascia, and posterior iliac crest.     * Insertion: Humerus (intertubercular groove).     * Innervation: $C6-C8$ thoracodorsal nerve.     * Action: Shoulder EXT, ADD, and internal rotation (IR).

• Pectoralis Major     * Origin: Medial half of clavicle, sternum, and cartilage of $1$st-$6$th Ribs.     * Insertion: Humerus (greater tubercle).     * Innervation: Upper fibers: $C5-C7$ (lateral pectoral); Lower fibers: $C6-T1$ (medial and lateral pectoral).     * Action (All fibers): Shoulder ADD, IR; Elevation of thorax in forced inspiration.     * Action (Upper fibers): FLEX, horizontal ADD.     * Action (Lower fibers): Shoulder EXT.

• Pectoralis Minor     * Origin: Ribs $3-5$.     * Insertion: Scapula (medial surface of coracoid process).     * Innervation: $C6-T1$ medial and lateral pectoral nerves.     * Action: Scapular ABD, depression, downward rotation; Elevation of ribs in forced inspiration when the scapula is fixed.

• Anterior Deltoid     * Origin: Lateral $1/3$ of clavicle, acromion, and spine of scapula.     * Insertion: Humerus (deltoid tuberosity).     * Innervation: $C5-C6$ axillary (ventral rami).     * Action: Shoulder ABD, FLEX, IR, and horizontal ADD.

• Middle Deltoid     * Origin: Lateral $1/3$ of clavicle, acromion, and spine of scapula.     * Insertion: Humerus (deltoid tuberosity).     * Innervation: $C5-C6$ axillary (ventral rami).     * Action: Shoulder ABD.

• Posterior Deltoid     * Origin: Scapula (spine on lower lip of posterior border).     * Insertion: Humerus (deltoid tuberosity).     * Innervation: $C5-C6$ axillary (ventral rami).     * Action: Shoulder ABD, EXT, external rotation (ER), and horizontal ABD.

• Coracobrachialis     * Origin: Scapula (coracoid process).     * Insertion: Humerus (medial border of mid shaft).     * Innervation: $C6-C7$ (musculocutaneous).     * Action: Shoulder FLEX and ADD.

• Teres Major     * Origin: Inferior angle and lower $1/3$ of lateral border of the scapula.     * Insertion: Humerus (lesser tubercle).     * Innervation: $C5-C6$ subscapular (upper and lower).     * Action: Shoulder IR, ADD, and EXT.

• Supraspinatus     * Origin: Scapula (supraspinous fossa).     * Insertion: Humerus (greater tubercle).     * Innervation: $C5-C6$ suprascapular.     * Action: Shoulder ABD and stabilizes the glenohumeral (GH) joint.

• Infraspinatus     * Origin: Scapula (infraspinous fossa).     * Insertion: Humerus (greater tubercle).     * Innervation: $C5-C6$ suprascapular.     * Action: Shoulder ER, ADD, and stabilizes the GH joint.

• Teres Minor     * Origin: Scapula (proximal $2/3$ of axillary border).     * Insertion: Humerus (greater tubercle).     * Innervation: $C5-C6$ axillary.     * Action: Shoulder ER, ADD, and stabilizes the GH joint.

• Subscapularis     * Origin: Scapula (subscapular fossa).     * Insertion: Humerus (lesser tubercle).     * Innervation: $C6$ lower subscapular.     * Action: Shoulder IR; Stabilization of the GH joint.

• Subclavius     * Origin: $1$st Rib and cartilage.     * Insertion: Inferior surface of middle $1/3$ of clavicle.     * Innervation: Subclavian $C5-C6$.     * Action: Depress clavicle; Elevate $1$st rib; Stabilize the sternoclavicular (SC) joint.

Muscles of the Elbow, Forearm, and Wrist

• Biceps Brachii     * Origin: Short Head: Scapula (coracoid process); Long head: Supraglenoid tubercle of scapula.     * Insertion: Radius (radial tuberosity) and bicipital aponeurosis.     * Innervation: $C5-C6$ musculocutaneous.     * Action: Elbow FLEX; Supination (SUP) of forearm; Shoulder FLEX.

• Brachialis     * Origin: Humerus (shaft: distal $\frac{1}{2}$ of anterior surface).     * Insertion: Ulna (ulnar tuberosity and coronoid process, anterior aspect).     * Innervation: $C5-C6$ musculocutaneous.     * Action: Elbow FLEX in a pronated forearm position.

• Triceps Brachii     * Origin: Long Head: Scapula (infraglenoid tuberosity); Lateral Head: Posterior surface of proximal $\frac{1}{2}$ of humerus; Medial Head: Posterior surface of distal humerus.     * Insertion: Ulna (olecranon process).     * Innervation: $C7-C8$ Radial.     * Action: All heads carry out elbow EXT; Long head assists in shoulder ADD and EXT.

• Brachioradialis     * Origin: Humerus (proximal $2/3$ of lateral supracondylar ridge).     * Insertion: Radius (styloid process).     * Innervation: $C5-C6$ radial nerve.     * Action: Elbow FLEX in neutral position; Assists with pronation and supination.

• Anconeus     * Origin: Humerus (lateral epicondyle).     * Insertion: Ulna (olecranon and posterior surface).     * Innervation: $C7-C8$ Radial.     * Action: Elbow EXT.

• Supinator     * Origin: Lateral epicondyle of humerus, RCL, annular ligament, and supinator crest of the ulna.     * Insertion: Anterior and lateral surface of the proximal $1/3$ of the radial shaft.     * Innervation: $C6-C7$ radial (posterior interosseous branch).     * Action: Supination of the forearm.

• Pronator Teres     * Origin: Common flexor tendon from medial epicondyle of humerus and coronoid process of the ulna.     * Insertion: Radius (middle and lateral surface).     * Innervation: $C6-C7$ Median.     * Action: Forearm pronation; Assists in elbow FLEX.

• Pronator Quadratus     * Origin: Medial, anterior surface of distal ulna.     * Insertion: Lateral, anterior surface of distal radius.     * Innervation: $C7-C8, T1$ median (anterior interosseous branch).     * Action: Forearm pronation.

• Extensor Carpi Radialis Longus     * Origin: Humerus (distal $1/3$ of lateral supracondylar ridge).     * Insertion: $2$nd Metacarpal (dorsal surface of base).     * Innervation: $C6-C7$ radial.     * Action: Wrist EXT and radial deviation (ABD); Assists elbow FLEX.

• Extensor Carpi Radialis Brevis     * Origin: Humerus (lateral epicondyle via common extensor tendon).     * Insertion: $3$rd Metacarpal (dorsal surface of base).     * Innervation: $C6-C7$ Radial.     * Action: Wrist EXT and radial deviation (ABD); Assists elbow FLEX.

• Extensor Carpi Ulnaris     * Origin: Humerus (lateral epicondyle via common extensor tendon).     * Insertion: $5$th Metacarpal (base).     * Innervation: $C7-C8$ Radial.     * Action: Wrist EXT and ulnar deviation (ADD).

• Flexor Carpi Radialis     * Origin: Humerus (common flexor tendon of the medial epicondyle).     * Insertion: $2$nd and $3$rd Metacarpals (base, palmar surface).     * Innervation: $C6-C7$ Median.     * Action: Wrist FLEX and radial deviation (ABD); Assists in elbow FLEX.

• Palmaris Longus     * Origin: Humerus (medial epicondyle via common flexor tendon).     * Insertion: Flexor Retinaculum and Palmar aponeurosis.     * Innervation: $C7-C8$ Median.     * Action: Tense the palmar fascia; Wrist FLEX; Assist elbow FLEX.

• Flexor Carpi Ulnaris     * Origin: Humeral head: Medial epicondyle via common flexor tendon; Ulnar head: Ulna (olecranon, posterior surface of proximal $2/3$ of ulna).     * Insertion: Pisiform, Hook of the Hamate, and the base of the $5$th Metacarpal.     * Innervation: $C7-T1$ Ulnar.     * Action: Wrist FLEX and ulnar deviation (ADD); Assist elbow FLEX.

Muscles of the Digits

• Extensor Digitorum     * Origin: Humerus (lateral epicondyle via common extensor tendon).     * Insertion: Bases of middle and distal phalanges of digits $2-5$.     * Innervation: $C6, C7, C8$ Radial.     * Action: Digits $2-5$: EXT of MP, PIP, and DIP; Assists wrist EXT.

• Extensor Indicis     * Origin: Ulna (posterior shaft) and Interosseous membrane.     * Insertion: Tendon of the extensor digitorum at the level of the $2$nd metacarpal.     * Innervation: $C7-C8$ Radial.     * Action: $2$nd Digit: MP and IP EXT, ADD; Assists in wrist EXT.

• Flexor Digitorum Superficialis     * Origin: Common flexor tendon from the medial epicondyle of humerus, UCL, coronoid process of ulna, interosseous membrane, and proximal shaft of radius.     * Insertion: Sides of middle phalanges of $2$nd-$5$th fingers.     * Innervation: $C7, C8, T1$ Median.     * Action: Digits $2-5$ FLEX of PIP and MP; Wrist FLEX (accessory).

• Flexor Digitorum Profundus     * Origin: Anterior and medial surfaces of proximal $\frac{3}{4}$ of ulna.     * Insertion: Bases of distal phalanges, palmar surface of $2$nd-$5$th fingers.     * Innervation: Digits $2$ and $3$: $C8-T1$ Median (anterior interosseous); Digits $4$ and $5$: $C8-T1$ Ulnar.     * Action: Digits $2-5$ FLEX of DIP, MP, and PIP (assist); Wrist FLEX (accessory).

• Extensor Digiti Minimi     * Origin: Common Extensor Tendon.     * Insertion: Digit $5$ radial and dorsal side of proximal phalanx.     * Innervation: $C7-C8$ Radial.     * Action: Digit $5$ DIP, MP, PIP: EXT and ABD; Assist wrist EXT.

• Abductor Digiti Minimi     * Origin: Pisiform and Tendon of flexor carpi ulnaris.     * Insertion: $5$th digit (proximal phalanx base on ulnar side).     * Innervation: $C8-T1$ Ulnar.     * Action: Digit $5$: ABD and Opposition.

• Flexor Digiti Minimi Brevis     * Origin: Hamate (hook) and Flexor retinaculum.     * Insertion: $5$th Digit (base of proximal phalanx, palmar surface).     * Innervation: $C8-T1$ Ulnar.     * Action: Digit $5$: MP FLEX and Opposition.

• Opponens Digiti Minimi     * Origin: Hamate (hook) and Flexor retinaculum.     * Insertion: $5$th Metacarpal (shaft on ulnar side).     * Innervation: $C8-T1$ Ulnar.     * Action: Opposition of the $5$th digit.

Intrinsic Hand Muscles (Lumbricals and Interossei)

• Lumbricals     * Origin: Surfaces of the flexor digitorum profundus tendons.     * Insertion: Extensor aponeurosis on dorsal surface of phalanges.     * Innervation: $2$nd and $3$rd fingers: Medial $C8, T1$; $4$th and $5$th fingers: Ulnar $C8-T1$.     * Action: Extend $2$nd-$5$th at IP joints; Flex $2$nd-$5$th at MP joints.

• Dorsal Interossei     * Origin: Adjacent sides of all metacarpals.     * Insertion: Base of the proximal phalanx of the $2$nd, $3$rd, and $4$th fingers and the extensor aponeurosis.     * Innervation: $C8-T1$ Ulnar.     * Action: $2$nd, $3$rd, and $4$th digits MP joints: ABD and FLEX; EXT at the IP joints.

• Palmar (Volar) Interossei     * Origin: Base of $1$st, $2$nd, $4$th, and $5$th Metacarpals.     * Insertion: Base of the proximal phalanx of the related finger and the extensor aponeurosis.     * Innervation: $C8-T1$ Ulnar.     * Action: $1$st, $2$nd, $4$th, $5$th ADD; MP FLEX; IP EXT.

Muscles of the Thumb (Pollicis Group)

• Abductor Pollicis Longus     * Origin: Posterior surface of the radius and ulna, and interosseous membrane.     * Insertion: $1$st Metacarpal (base).     * Innervation: $C7-C8$ Radial.     * Action: $1$st CMC ABD and EXT; Wrist radial deviation (ABD).

• Extensor Pollicis Longus     * Origin: Posterior surface of ulna and Interosseous Membrane.     * Insertion: Thumb (base of distal phalanx, dorsal).     * Innervation: $C7-C8$ Radial.     * Action: EXT of thumb at IP, MP, CMC; Wrist radial deviation (ABD).

• Extensor Pollicis Brevis     * Origin: Posterior surface of the Radius and Interosseous Membrane.     * Insertion: Thumb (proximal phalanx base, dorsal).     * Innervation: $C7-C8$ Radial.     * Action: Thumb MP EXT; $1$st CMC EXT; Wrist radial deviation (ABD).

• Flexor Pollicis Longus     * Origin: Anterior surface of Radius and interosseous membrane.     * Insertion: Thumb (base of distal phalanx, palmar side).     * Innervation: $C8-T1$ Median (anterior interosseous).     * Action: Thumb IP, MP, CMC FLEX; Assist in wrist FLEX.

• Flexor Pollicis Brevis     * Origin: Superficial Head: Flexor Retinaculum; Deep Head: Trapezoid, Capitate, and Trapezium.     * Insertion: Thumb (base of proximal phalanx).     * Innervation: Superficial: Median $C6-T1$; Deep: Ulnar $C8-T1$.     * Action: Thumb MP and CMC FLEX; Opposition.

• Abductor Pollicis Brevis     * Origin: Flexor retinaculum; Scaphoid (tubercle); Trapezium (tubercle).     * Insertion: Thumb (base of proximal phalanx).     * Innervation: $C6-T1$ Median.     * Action: Thumb CMC and MP ABD; Opposition.

• Opponens Pollicis     * Origin: Trapezium (tubercle) and Flexor retinaculum.     * Insertion: $1$st Metacarpal (radial side).     * Innervation: $C8-T1$ Median.     * Action: Thumb Opposition.

• Adductor Pollicis     * Origin: Capitate, $2$nd and $3$rd metacarpals.     * Insertion: Thumb (base, proximal phalanx, ulnar side).     * Innervation: $C8-T1$ Ulnar.     * Action: Thumb CMC and MP ADD; Assist in MP FLEX.