Upper Extremity Anatomy - Origins, Insertions, Innervations, Actions (OIIA) - Shoulder to Hand Muscles

Shoulder & Scapula Muscles (OIIA)

  • Deltoid

    • Origin: Clavicle, acromion, spine of scapula

    • Insertion: Deltoid tuberosity

    • Innervation / Action: Axillary n. / Abduction, flex, ext{extend}

    • Notes: Primary abductor of the arm after initial stabilization and the shoulder girdle; important for shoulder range of motion.

  • Supraspinatus

    • Origin: Supraspinous fossa

    • Insertion: Greater tubercle

    • Innervation / Action: Suprascapular n. / Initiates abduction, GH restabilizer

    • Notes: Initiates first rupture-free abduction; key stabilizer of the glenohumeral joint.

  • Infraspinatus

    • Origin: Infraspinous fossa

    • Insertion: Greater tubercle

    • Innervation / Action: Suprascapular n. / External rotation, GH restabilizer

    • Notes: Lateral rotator; stabilizes humeral head in glenoid.

  • Teres Minor

    • Origin: Lateral border of scapula

    • Insertion: Greater tubercle

    • Innervation / Action: Axillary n. / External rotation, GH restabilizer

    • Notes: Assists in external rotation; contributes to stability of the shoulder.

  • Subscapularis

    • Origin: Subscapular fossa

    • Insertion: Lesser tubercle

    • Innervation / Action: Subscapular n. / Internal rotation, GH restabilizer

    • Notes: Major internal rotator; stabilizes humeral head anteriorly.

  • Teres Major

    • Origin: Inferior angle of scapula

    • Insertion: Medial lip of intertubercular sulcus

    • Innervation / Action: Lower subscapular n. / Adduction, IR

    • Notes: Works with latissimus dorsi in adduction and internal rotation.

  • Serratus Anterior

    • Origin: Ribs 1-8

    • Insertion: Medial border of scapula

    • Innervation / Action: Long horacic n. / Protraction, upward rotation

    • Notes: Essential for scapular protraction and upward rotation; prevents scapular winging.

  • Trapezius

    • Origin: Occipital bone, C7–T12 spines

    • Insertion: Clavicle, acromion, spine of scapula

    • Innervation / Action: CN ext{ XI} / Elevates, retracts, depresses scapula

    • Notes: Upper/mmiddle/lower fibers contribute to scapular movement and posture.

  • Latissimus Dorsi

    • Origin: Spinous processes of T8-T12

    • Insertion: Intertubercular sulcus of humerus

    • Innervation / Action: Thoracodorsal n. / Extends, adducts, internally rotates

    • Notes: Powerful humeral extension and adduction; works with pectoral muscles during pushing activities.

  • Levator Scapulae

    • Origin: Posterior tubercles of transverse processes C1-C4

    • Insertion: Medial border of scapula

    • Innervation / Action: Dorsal scapular n. (C4, C5) + Cervical
      $C3$, $C4$/ Elevates and rotates scapula

    • Notes: Elevates scapula; contributes to downward rotation when acting singly.

  • Rhomboid Major

    • Origin: Spinous processes T2-T5

    • Insertion: Medial border of scapula

    • Innervation / Action: Dorsal scapular n. / Retracts
      and rotates scapula

    • Notes: Retracts scapula; contributes to retraction and stabilization of the scapular girdle.

  • Rhomboid Minor

    • Origin: Nuchal ligament, spinous process C7-T1

    • Insertion: Medial end of scapular spine

    • Innervation / Action: Dorsal scapular n. / Retracts
      and rotates scapula

    • Notes: Finely adjusts scapular position for precise orientation.

  • Pectoralis Major

    • Origin: Clavicular head

    • Insertion: Intertubercular sulcus of humerus

    • Innervation / Action: Lateral + medial
      actoral nerves (C5–C8) / Adduction, IR, scapular protraction, depression, humeral flexion and extension

    • Notes: Large chest muscle contributing to shoulder and arm movements; acts on humerus.

  • Pectoralis Minor

    • Origin: Ribs 3-5

    • Insertion: Coracoid process of scapula

    • Innervation / Action: Pectoral n. (C8-T1) / Stabilizes scapula

    • Notes: Stabilizes the scapula by drawing it anteriorly and inferiorly.

  • Subclavius

    • Origin: 1st rib

    • Insertion: Clavicle

    • Innervation / Action: Nerve
      to subclavius (C5, C6) / Anchors + depresses scapula + clavicle

    • Notes: Helps stabilize the clavicle and scapulothoracic articulation.

Arm Muscles

  • Biceps Brachii

    • Origin: Coracoid (short head), supraglenoid (long head)

    • Insertion: Radial tuberosity

    • Innervation / Action: Musculocutaneous n. / Elbow flexion, supinate forearm, stabilize shoulder

    • Notes: Long head crosses shoulder; short head helps flex and supinate; major forearm flexor when supinated.

  • Brachialis

    • Origin: Anterior humerus

    • Insertion: Ulnar tuberosity, coronoid

    • Innervation / Action: Musculocutaneous n. / Elbow flexion

    • Notes: Primary elbow flexor, independent of forearm position.

  • Coracobrachialis

    • Origin: Coracoid process

    • Insertion: Medial humerus

    • Innervation / Action: Musculocutaneous n. / Flex, adduct arm

    • Notes: Assists in flexion and adduction of the arm at the shoulder.

  • Triceps Brachii

    • Origin: Infraglenoid (long head); lateral & medial heads from posterior humerus

    • Insertion: Olecranon

    • Innervation / Action: Radial n. / Elbow extension + shoulder stabilization

    • Notes: Primary elbow extensor; long head crosses shoulder joint.

  • Pronator Quadratus

    • Origin: Ulna (anterior)

    • Insertion: Radius

    • Innervation / Action: Anterior
      Interosseous n. / Stabilizes distal Radius + Ulna
      / Pronation of forearm

  • Anconeus

    • Origin: Lateral epicondyle

    • Insertion: Olecranon

    • Innervation / Action: Radial n. / Assists triceps with elbow extension

    • Notes: Assists elbow extension; stabilizes elbow joint.

  • Supinator

    • Origin: Lateral epicondyle, ulna

    • Insertion: Radius (proximal)

    • Innervation / Action: Posterior
      Interosseous n. / Supinates forearm

  • Brachioradialis

    • Origin: Supracondylar ridge of humerus

    • Insertion: Distal radius

    • Innervation / Action: Radial n. / Elbow flexion when elbow is neutral

    • Notes: Optimally active when forearm is in a mid-position between pronation and supination.

Forearm Flexors (Anterior)

  • Pronator Teres

    • Origin: Coronoid process

    • Insertion: Radius

    • Innervation / Action: Median n. / Pronation of forearm, elbow flexion

  • Flexor Carpi Radialis (FCR)

    • Origin: Medial epicondyle of humerus

    • Insertion: Base of 2^{nd} and 3^{rd} metacarpals

    • Innervation / Action: Median n./ flexes and abducts wrist

  • Palmaris Longus

    • Origin: Medial epicondyle

    • Insertion: Flexor retinaculum, palmar aponeurosis

    • Innervation / Action: Median n./ flexes wrist, tenses palmar aponeurosis

  • Flexor Carpi Ulnaris (FCU)

    • Origin: Medial epicondyle; ulnar head, olecranon

    • Insertion: Pisiform, hook of hamate, 5th metacarpal

    • Innervation / Action: Ulnar n./ flexes and adducts wrist

Note: There is a misprint in some sources listing “Flexor Capri Radialis”; this is Flexor Carpi Radialis (FCR).

Forearm Extensors (Posterior)

  • Brachioradialis

    • Origin: Lateral supracondylar ridge

    • Insertion: Distal radius

    • Innervation / Action: Radial n. / Flex elbow

  • Extensor Carpi Radialis Longus (ECRL)

    • Origin: Lateral supracondylar ridge of humerus

    • Insertion: Base of 2^{nd} metacarpal (dorsal)

    • Innervation / Action: Radial n./ Wrist ext. + Radial Deviation

  • Extensor Carpi Radialis Brevis (ECRB)

    • Origin: Lateral epicondyle of humerus

    • Insertion: Base of 3^{rd} metacarpal

    • Innervation / Action: Radial n./ Wrist Ext and Radial Deviation

  • Extensor Digitorum

    • Origin: Lateral epicondyle

    • Insertion: Extensor expansions of digits 2–5

    • Innervation / Action: Posterior
      i nterosseous n. / Extends fingers

  • Extensor Digiti Minimi

    • Origin: Lateral epicondyle

    • Insertion: Extensor expansion of digit 5

    • Innervation / Action: Posterior
      i nterosseous n. / Extend little finger

  • Extensor Carpi Ulnaris (ECU)

    • Origin: Lateral epicondyle

    • Insertion: Base of 5^{th} metacarpal

    • Innervation / Action: Posterior
      i nterosseous n./ Extend, abduct wrist

  • Supinator

    • Origin: Lateral epicondyle, ulna

    • Insertion: Radius (proximal)

    • Innervation / Action: Posterior
      i nterosseous n./ Supinates

  • Abductor Pollicis Longus

    • Origin: Ulna, Radius, Interosseous membrane (IO)

    • Insertion: Base of 1^{st} metacarpal

    • Innervation / Action: Posterior
      i nterosseous n./ Abduct thumb

  • Extensor Pollicis Brevis

    • Origin: Radius

    • Insertion: Proximal phalanx of thumb

    • Innervation / Action: Posterior
      i nterosseous n./ Extend thumb

  • Extensor Pollicis Longus

    • Origin: Ulna

    • Insertion: Distal phalanx of thumb

    • Innervation / Action: Posterior
      i nterosseous n./ Extend thumb

  • Extensor Indicis

    • Origin: Ulna

    • Insertion: Extensor expansion of digit 2

    • Innervation / Action: Posterior
      i nterosseous n./ Extend index

Wrist Muscles

  • Flexor Carpi Radialis (FCR)

    • Origin: Medial epicondyle

    • Insertion: Base of 2^{nd} and 3^{rd} metacarpals

    • Innervation / Action: Median n./ Wrist flex + radial deviation

  • Flexor Carpi Ulnaris (FCU)

    • Origin: Medial epicondyle

    • Insertion: Base of 5^{th} metacarpal (pisiform + hamate)

    • Innervation / Action: Ulnar n./ Wrist flex + ulnar deviation

  • Palmaris Longus

    • Origin: Medial epicondyle

    • Insertion: Palmar aponeurosis / Flexor retinaculum

    • Innervation / Action: Median n./ Wrist flex + stabilization of palmar aponeurosis

  • Extensor Digiti Minimi

    • Origin: Lateral epicondyle

    • Insertion: Extensor expansion of digit 5

    • Innervation / Action: Posterior
      i nterosseous n./ Extend little finger

Hand Muscles

  • Abductor Pollicis Brevis

    • Origin: Flexor retinaculum, scaphoid, trapezium

    • Insertion: Base of proximal phalanx of thumb (lateral side)

    • Innervation / Action: Median n./ Abducts thumb

  • Flexor Pollicis Brevis

    • Origin: Flexor Retinaculum

    • Insertion: Proximal phalanx

    • Innervation / Action: Superficial head (median n.)
      Deep head (ulnar n.) / flexion

  • Opponens Pollicis

    • Origin: Flexor retinaculum

    • Insertion: Lateral side of 1st metacarpal

    • Innervation / Action: Median n./ Opposes thumb

  • Abductor Digiti Minimi

    • Origin: Pisiform

    • Insertion: Base of proximal phalanx

    • Innervation / Action: Ulnar n./ Abducts little finger

  • Flexor Digiti Minimi Brevis

    • Origin: Hook of hamate / flexor retinaculum

    • Insertion: Base of proximal phalanx

    • Innervation / Action: Ulnar n./ Flexion of MCP

  • Flexor Digitorum Superficialis (Flexor Digiti Superfici)

    • Origin: Medial epicondyle of humerus

    • Insertion: Volar middle phalanx for digits 2–5

    • Innervation / Action: Median n./ PIP flexion of digits 2–5

  • Flexor Digitorum Profundus

    • Origin: Medial ulna

    • Insertion: Volar distal phalanx

    • Innervation / Action: Anterior
      i nterosseous n. (Index, Long) Ulnar
      (Ring, Small) / Flex DIP + PIP

  • Opponens Digiti Minimi

    • Origin: Hook of hamate / flexor retinaculum

    • Insertion: Medial border of the 5th metacarpal

    • Innervation / Action: Ulnar n./ Opposes little finger

  • Flexor Pollicis Longus

    • Origin: Interosseous membrane

    • Insertion: Distal phalanx of thumb

    • Innervation / Action: Anterior
      i nterosseous n./ Thumb IP flexion

  • Extensor Pollicis Longus

    • Origin: Posterior ulna + interosseous membrane

    • Insertion: Dorsal distal phalanx of the thumb

    • Innervation / Action: Posterior
      Interosseous n./ Extend at MP & IP joints of thumb

  • Lumbricals

    • Origin: Tendons of flexor digitorum profundus

    • Insertion: Lateral bands of extensor expansion for digits 2–5

    • Innervation / Action: 1st & 2nd n./ Median n. , 3rd & 4th n./ Ulnar n. / Flex MCP, Extend IPs

  • Dorsal Interossei (4)

    • Origin: Metacarpals

    • Insertion: Proximal phalanges, extensor expansions of digits 2–4

    • Innervation / Action: Ulnar n./ Abduct fingers (DAB), assists
      lumbricals

  • Palmar Interossei (3)

    • Origin: Metacarpals

    • Insertion: Proximal phalanges, extensor expansions

    • Innervation / Action: Ulnar n./ Adducts fingers (PAD), assist lumbricals

  • Adductor Pollicis

    • Origin: Oblique head / Transverse head

    • Insertion: Proximal phalanx of thumb

    • Innervation / Action: Ulnar n./ Adducts thumb

Key concepts, connections, and context

  • OIIA framework: Origins, Insertions, Innervations, Actions provide a unified view of how muscles contribute to shoulder, arm, forearm, wrist, and hand movements.

  • Scapulohumeral coordination: Several shoulder girdle muscles (e.g., Serratus Anterior, Trapezius, Rhomboids) coordinate with the rotator cuff (Supraspinatus, Infraspinatus, Teres Minor, Subscapularis) to stabilize the glenohumeral joint during arm elevation and rotation.

  • Rotator cuff roles: Supraspinatus initiates abduction; Infraspinatus and Teres Minor external rotate; Subscapularis internal rotation; together they stabilize the humeral head during movement.

  • Scapular motion and arm function: Upward rotation and stabilization of the scapula by Serratus Anterior and Trapezius support full arm elevation; dyskinesias can impair shoulder mechanics.

  • Nerve considerations: Nerve roots and nerves listed (e.g., Axillary, Suprascapular, Dorsal Scapular, Thoracodorsal, Median, Ulnar, PIN) reflect common pathways for motor supply and potential injury patterns.

  • Functional divisions: Distinct compartments (anterior flexors, posterior extensors, intrinsic hand muscles) illustrate the serial organization from proximal to distal segments of the upper limb.

  • Interconnections with anatomy principles: Proximal stability (scapula, clavicle) enables distal mobility (hand function); many forearm muscles cross the wrist and contribute to wrist and finger movements in addition to elbow/shoulder actions.

Notation and LaTeX usage in this study guide

  • Numerical ranges and specific spinal/nerve levels are represented in LaTeX, e.g.:

    • Ribs 1-8

    • Spinal levels C7–T12

    • Nerve roots C5-C8, C8-T1

    • Metacarpal numerals 2^{nd}, 3^{rd}, 5^{th}, etc.

  • Muscle actions are described succinctly; where applicable, anatomical terms are kept precise (e.g., MCP, PIP, DIP, IP joints).

Clinical relevance reminders (quick recall):

  • Supraspinatus tendinopathy or tear often limits initial shoulder abduction; rely on the deltoid after initiation.

  • Axillary nerve injury can weaken deltoid and teres minor functions, affecting abduction and external rotation.

  • Long thoracic nerve injury impairs Serratus Anterior → scapular winging and reduced upward rotation during arm elevation.

  • Ulnar nerve lesions impact intrinsic hand muscles (interossei, lumbricals 3–4), affecting finger abduction/adduction and grip finesse.

  • Median nerve injuries can affect thenar muscles (e.g., Abductor Pollicis Brevis, Flexor Pollicis Brevis) and lumbricals 1–2, influencing thumb opposition and index finger flexion.

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