Shoulder and Upper Extremity Muscles

• Muscles of the shoulder and upper extremity facilitate movements like flexion, extension, abduction, adduction, rotation, pronation, and supination.
• These muscles are grouped by location and function into shoulder, arm, forearm, and hand muscles.
• Understanding each muscle's origin, insertion, nerve supply, and action is vital for comprehending upper extremity function.

Shoulder Muscles

• Pectoral girdle movement is enabled by the trapezius, rhomboids, levator scapulae, serratus anterior, and pectoralis minor.
• Arm movement is enabled by the deltoid, supraspinatus, infraspinatus, teres minor, subscapularis, teres major, latissimus dorsi, pectoralis major, and coracobrachialis.

Trapezius

• Originates from the occipital bone, ligamentum nuchae, and spinous processes of C7-T12 vertebrae.
• Inserts on the lateral third of the clavicle, acromion, and scapular spine.
• Innervated by the accessory nerve (CN XI) and cervical spinal nerves (C3-C4).
• Action includes elevation, retraction, and rotation of the scapula, and head extension.

Rhomboids (Major and Minor)

• Originates from spinous processes of C7-T5 vertebrae.
• Inserts on the medial border of the scapula.
• Innervated by the dorsal scapular nerve.
• Responsible for scapular retraction and elevation.

Levator Scapulae

• Originates from transverse processes of C1-C4 vertebrae.
• Inserts on the medial border of the scapula, superior to the spine.
• Innervated by the dorsal scapular nerve and cervical spinal nerves (C3-C4).
• Elevates and downwardly rotates the scapula.

Serratus Anterior

• Originates from ribs 1-8 (or 9).
• Inserts on the medial border of the scapula (anterior surface).
• Innervated by the long thoracic nerve.
• Protraction and upward rotation of the scapula; holds scapula against the thoracic wall.

Pectoralis Minor

• Originates from ribs 3-5.
• Inserts on the coracoid process of the scapula.
• Innervated by the medial pectoral nerve.
• Protraction and depression of the scapula; elevates ribs during forced inspiration.

Deltoid

• Originates from the lateral third of the clavicle, acromion, and scapular spine.
• Inserts on the deltoid tuberosity of the humerus.
• Innervated by the axillary nerve.
• Abducts the arm; anterior fibers flex and medially rotate; posterior fibers extend and laterally rotate.

Supraspinatus

• Originates from the supraspinous fossa of the scapula.
• Inserts on the greater tubercle of the humerus.
• Innervated by the suprascapular nerve.
• Abducts the arm; stabilizes the shoulder joint.

Infraspinatus

• Originates from the infraspinous fossa of the scapula.
• Inserts on the greater tubercle of the humerus.
• Innervated by the suprascapular nerve.
• Laterally rotates the arm; stabilizes the shoulder joint.

Teres Minor

• Originates from the lateral border of the scapula.
• Inserts on the greater tubercle of the humerus.
• Innervated by the axillary nerve.
• Laterally rotates the arm; stabilizes the shoulder joint.

Subscapularis

• Originates from the subscapular fossa of the scapula.
• Inserts on the lesser tubercle of the humerus.
• Innervated by the upper and lower subscapular nerves.
• Medially rotates the arm; stabilizes the shoulder joint.

Teres Major

• Originates from the inferior angle of the scapula.
• Inserts on the intertubercular groove of the humerus.
• Innervated by the lower subscapular nerve.
• Adducts, extends, and medially rotates the arm.

Latissimus Dorsi

• Originates from spinous processes of T7-L5 vertebrae, thoracolumbar fascia, iliac crest, and ribs 9-12.
• Inserts on the intertubercular groove of the humerus.
• Innervated by the thoracodorsal nerve.
• Adducts, extends, and medially rotates the arm; draws the shoulder downward and backward.

Pectoralis Major

• Originates from the clavicular head (medial half of clavicle) and sternocostal head (sternum, ribs 1-6/7, and aponeurosis of external oblique muscle).
• Inserts on the intertubercular groove of the humerus.
• Innervated by the medial and lateral pectoral nerves.
• Adducts, flexes, and medially rotates the arm; clavicular head also flexes the arm.

Coracobrachialis

• Originates from the coracoid process of the scapula.
• Inserts on the medial surface of the humerus.
• Innervated by the musculocutaneous nerve.
• Flexes and adducts the arm.

Arm Muscles

• Responsible primarily for flexion and extension at the elbow joint.
• Located in the anterior and posterior compartments of the arm.
• Anterior compartment: biceps brachii, brachialis, and coracobrachialis.
• Posterior compartment: triceps brachii.
• The brachialis is the primary flexor of the forearm.

Biceps Brachii

• Originates from the short head (coracoid process of scapula) and long head (supraglenoid tubercle of scapula).
• Inserts on the radial tuberosity and bicipital aponeurosis.
• Innervated by the musculocutaneous nerve.
• Flexes and supinates the forearm; also flexes the arm.

Brachialis

• Originates from the anterior surface of the humerus (distal half).
• Inserts on the ulnar tuberosity and coronoid process of the ulna.
• Innervated by the musculocutaneous and radial nerves.
• Flexes the forearm.

Triceps Brachii

• Originates from the long head (infraglenoid tubercle of scapula), lateral head (posterior humerus above radial groove), and medial head (posterior humerus below radial groove).
• Inserts on the olecranon process of the ulna.
• Innervated by the radial nerve.
• Extends the forearm; the long head also adducts and extends the arm.

Forearm Muscles

• Control wrist, hand, and finger movements.
• Divided into anterior and posterior compartments.
• Anterior compartment muscles are primarily responsible for flexion and pronation.
• Posterior compartment muscles are primarily responsible for extension and supination.
• Several anterior forearm muscles are innervated by the median nerve, posterior by the radial nerve.

Anterior Compartment Muscles (Superficial Layer)

• Pronator Teres
  • Originates from the medial epicondyle of the humerus and coronoid process of the ulna.
  • Inserts on the lateral surface of the radius (midshaft).
  • Innervated by the median nerve.
  • Pronates the forearm and assists in flexing the elbow.
• Flexor Carpi Radialis
  • Originates from the medial epicondyle of the humerus.
  • Inserts on the bases of metacarpals II and III.
  • Innervated by the median nerve.
  • Flexes and abducts the wrist.
• Palmaris Longus
  • Originates from the medial epicondyle of the humerus.
  • Inserts on the palmar aponeurosis.
  • Innervated by the median nerve.
  • Flexes the wrist and tenses the palmar aponeurosis.
• Flexor Carpi Ulnaris
  • Originates from the medial epicondyle of the humerus and olecranon of the ulna.
  • Inserts on the pisiform bone, hamate bone, and base of metacarpal V.
  • Innervated by the ulnar nerve.
  • Flexes and adducts the wrist.

Anterior Compartment Muscles (Intermediate Layer)

• Flexor Digitorum Superficialis
  • Originates from the medial epicondyle of the humerus, coronoid process of the ulna, and radial shaft.
  • Inserts on the middle phalanges of digits II-V (splits for profundus tendons).
  • Innervated by the median nerve.
  • Flexes the PIP joints of digits II-V, and also the MCP joints and wrist.

Anterior Compartment Muscles (Deep Layer)

• Flexor Digitorum Profundus
  • Originates from the proximal ulna shaft and interosseous membrane.
  • Inserts on the distal phalanges of digits II-V.
  • Innervated by the median nerve (lateral half) and ulnar nerve (medial half).
  • Flexes the DIP joints of digits II-V; also flexes the PIP and MCP joints, and the wrist.
• Flexor Pollicis Longus
  • Originates from the radius (anterior surface) and interosseous membrane.
  • Inserts on the distal phalanx of the thumb.
  • Innervated by the anterior interosseous nerve (branch of median nerve).
  • Flexes the IP joint of the thumb; also flexes the MCP and CMC joints.
• Pronator Quadratus
  • Originates from the distal ulna (anterior surface).
  • Inserts on the distal radius (anterior surface).
  • Innervated by the anterior interosseous nerve (branch of the median nerve).
  • Pronates the forearm.

Posterior Compartment Muscles (Superficial Layer)

• Brachioradialis
  • Originates from the lateral supracondylar ridge of the humerus.
  • Inserts on the distal radius (styloid process).
  • Innervated by the radial nerve.
  • Flexes the forearm (especially when pronated or supinated); also assists in pronation and supination.
• Extensor Carpi Radialis Longus
  • Originates from the lateral supracondylar ridge of the humerus.
  • Inserts on the base of metacarpal II.
  • Innervated by the radial nerve.
  • Extends and abducts the wrist.
• Extensor Carpi Radialis Brevis
  • Originates from the lateral epicondyle of the humerus.
  • Inserts on the base of metacarpal III.
  • Innervated by the deep branch of the radial nerve.
  • Extends and abducts the wrist.
• Extensor Digitorum
  • Originates from the lateral epicondyle of the humerus.
  • Inserts on the extensor hoods of digits II-V.
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Extends the MCP, PIP, and DIP joints of digits II-V; also extends the wrist.
• Extensor Digiti Minimi
  • Originates from the lateral epicondyle of the humerus.
  • Inserts on the extensor hood of digit V.
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Extends the MCP, PIP, and DIP joints of digit V; also assists in extending the wrist.
• Extensor Carpi Ulnaris
  • Originates from the lateral epicondyle of the humerus and ulna.
  • Inserts on the base of metacarpal V.
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Extends and adducts the wrist.

Posterior Compartment Muscles (Deep Layer)

• Supinator
  • Originates from the lateral epicondyle of the humerus and ulna.
  • Inserts on the radius (proximal third).
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Supinates the forearm.
• Abductor Pollicis Longus
  • Originates from the radius, ulna, and interosseous membrane.
  • Inserts on the base of metacarpal I.
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Abducts the thumb at the CMC joint; also extends the thumb.
• Extensor Pollicis Brevis
  • Originates from the radius and interosseous membrane.
  • Inserts on the base of the proximal phalanx of the thumb.
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Extends the MCP joint of the thumb; also abducts the thumb.
• Extensor Pollicis Longus
  • Originates from the ulna and interosseous membrane.
  • Inserts on the base of the distal phalanx of the thumb.
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Extends the IP joint of the thumb; also extends and abducts the thumb.
• Extensor Indicis
  • Originates from the ulna and interosseous membrane.
  • Inserts on the extensor hood of digit II.
  • Innervated by the deep branch of the radial nerve (posterior interosseous nerve).
  • Extends the MCP, PIP, and DIP joints of digit II; also assists in extending the wrist.

Hand Muscles

• Enable fine motor movements of the fingers and thumb.
• Divided into intrinsic and extrinsic muscles.
• Extrinsic muscles originate in the forearm and insert into the hand.
• Intrinsic muscles are located entirely within the hand.
• Intrinsic muscles are further divided into thenar, hypothenar, and intermediate groups.

Thenar Muscles

• Abductor Pollicis Brevis
  • Originates from the scaphoid and trapezium.
  • Inserts on the base of the proximal phalanx of the thumb.
  • Innervated by the recurrent branch of the median nerve.
  • Abducts the thumb.
• Flexor Pollicis Brevis
  • Originates from the trapezium and capitate.
  • Inserts on the base of the proximal phalanx of the thumb.
  • Innervated by the recurrent branch of the median nerve (superficial head) and ulnar nerve (deep head).
  • Flexes the thumb.
• Opponens Pollicis
  • Originates from the trapezium.
  • Inserts on metacarpal I.
  • Innervated by the recurrent branch of the median nerve.
  • Opposes the thumb.

Hypothenar Muscles

• Abductor Digiti Minimi
  • Originates from the pisiform.
  • Inserts on the base of the proximal phalanx of digit V.
  • Innervated by the ulnar nerve.
  • Abducts digit V.
• Flexor Digiti Minimi Brevis
  • Originates from the hamate.
  • Inserts on the base of the proximal phalanx of digit V.
  • Innervated by the ulnar nerve.
  • Flexes digit V.
• Opponens Digiti Minimi
  • Originates from the hamate.
  • Inserts on metacarpal V.
  • Innervated by the ulnar nerve.
  • Opposes digit V.

Intermediate Muscles

• Lumbricals
  • Originates from the tendons of the flexor digitorum profundus.
  • Inserts on the extensor hoods of digits II-V.
  • Innervated by the median nerve (lumbricals I and II) and ulnar nerve (lumbricals III and IV).
  • Flexes the MCP joints and extends the PIP and DIP joints of digits II-V.
• Palmar Interossei
  • Originates from the metacarpals.
  • Inserts on the bases of the proximal phalanges of digits II, IV, and V.
  • Innervated by the ulnar nerve.
  • Adducts digits II, IV, and V toward the midline of the hand; also flexes the MCP joints and extends the PIP and DIP joints.
• Dorsal Interossei
  • Originates from the adjacent sides of the metacarpals.
  • Inserts on the bases of the proximal phalanges of digits II-IV.
  • Innervated by the ulnar nerve.
  • Abducts digits II-IV from the midline of the hand; also flexes the MCP joints and extends the PIP and DIP joints.