Muscles of the Back

Anterior Axioappendicular MusclesPectoralis MajorOriginClavicular head: anterior surface of medial ½ of clavicleSternocostal head: anterior surface of sternum, superior 6 costal cartilages, aponeurosis of oblique muscle

InsertionLateral lip of intertubercular groove of humerus

InnervationLateral and medial nerves

ActionAdducts and medially rotates humerus;Draws scapula anteriorly and inferiorlyActing alone, clavicular head flexes humerus & sternocostal head extends it from the flexed position

Pectoralis MinorOrigin3rd -5th ribs near their costal cartilages

InsertionMedial border & superior surface of coracoid process of scapula

InnervationMedial pectoral nerve

ActionStabilizes scapula by drawing it inferiorly & anteriorly against thoracic wall

SubclaviusOriginJunction of 1st rib & its costal cartilage

InsertionInferior surface of middle 3rd of clavicle

InnervationNerve to subclavius

ActionAnchors & depresses clavicle

Serratus AnteriorOriginExternal surfaces of lateral parts of 1st-8th ribs

InsertionAnterior surface of medial border of scapula

InnervationLong thoracic nerve

ActionProtracts scapula and hold it against thoracic wall; rotates scapula

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Posterior Axioappendicular MusclesTrapeziusOriginMedial 3rd of superior nuchal lineExternal occipital protuberanceNuchal ligament, T7-T12 spinous processes

InsertionLateral 3rd of clavicle; acromion of spine of scapula

InnervationSpinal accessory nerve (CN X1)

Action ↓part elevates; ↑ depresses; middle part (or all parts together) retracts scapula; ↓ & ↑act together to rotate glenoid cavity superiorly

Latissimus DorsiOriginSpinous process of inferior 6 thoracic vertebraeThoracolumbar fascia, iliac crest, and inferior 3 or 4 ribs

InsertionFloor of intertubercular groove of humerus

InnervationThoracodorsal nerve

ActionExtends, adducts, & medially rotates humerusRaises body toward arms during climbing

Levator ScapulaeOriginPosterior tubercles of transverse processes of C1-C4

InsertionMedial border of scapula to root of spine

InnervationDorsal scapular and cervical nerves

ActionElevates scapula & tilts its glenoid cavity inferiorly by rotating scapula

Rhomboid major and MinorOrigin:Minor: nuchal ligament, spinous process of C7 and T1Major: spinous processes of T2-T5

InsertionMinor: smooth triangular area at medial end of scapular spineMajor: medial border of scapula from level of spine to inferior angle

InnervationDorsal scapular nerveActionRetract scapula & rotate it to depress glenoid cavity; fix scapula to thoracic wall

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Scapulohumeral (Intrinsic Shoulder) MusclesDeltoidOriginLateral 3rd of clavicle; acromion of spine of scapula

InsertionDeltoid tuberosity of humerus

InnervationAxillary Nerve

ActionClavicular part flexes & medially rotates arm; acromion part abducts arm; spinal part extends & laterally rotates arm

SupraspinatusOriginSupraspinous fossa of scapula

InsertionSuperior facet of greater tubercleInnervationSuprascapular nerve

ActionInitiates & assists deltoid in abduction of arm & acts with rotator cuff muscles

InfraspinatusOriginInfraspinous fossa of scapula

InsertionMiddle facet of greater tubercle

InnervationSuprascapular nerve

ActionLaterally rotate arm; help hold humeral head in glenoid cavity of scapula

Teres minorOriginMiddle part of lateral border of scapula

InsertionInferior face of greater tubercle

InnervationAxillary nerve

ActionSame as infraspinatus muscle

SubcapularisOriginSubscapular fossa

InsertionLesser tubercle of humerus

InnervationUpper & lower subscapular nerveActionMedially rotates & adducts arm; helps hold humeral head in glenoid cavity

Teres majorOriginPosterior surface of inferior angle of scapula

InsertionMedial lip of intertubercular groove of humerusInnervationLower subscapular nerve

ActionSame as infraspinatus muscle

Rotator cuff muscles: form a musculotendinous rotator cuff around glenohumeral joint. All except the supraspinatus muscle rotate the humerus. They all protect the joint and give it stability

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Muscles of ArmBiceps BrachiiOriginShort head: tip of coracoid process of scapulaLong head: supraglenoid tubercle of scapula

InsertionTuberosity of radius & fascia of forearm via bicipital aponeurosis

InnervationMusculocutaneous nerve

ActionSupinates forearm &, when it is supine, flexes forearm; short head resists shoulder dislocation

BrachialisOriginDistal ½ of anterior surface of humerus

InsertionCoronoid process & tuberosity of ulna

InnervationMusculotaneous nerve

ActionFlexes forearm in all positions (during slow and quick movement: greatest force)

CoracobrachialisOriginTip of coracoid process of scapula

InsertionMiddle 3rd of medial surface of humerus

InnervationMusculocutaneous nerve

ActionHelps flex & adduct arm; resists dislocation of shoulder (stabilizes glenohumeral joint)

Triceps BrachiiOriginLong head: infraglenoid tubercle of scapulaLateral head: posterior surface of humerus, superior to radial grooveMedial head: posterior surface of humerus, inferior to radial grooveInsertionProximal end of olecranon of ulna & fascia of forearm

InnervationRadial nerve

ActionChief extensor of forearm; long head resists dislocation of humerus; esp important during abduction

AnconeusOriginLateral epicondyle of humerus

InsertionLateral surface of olecranon & superior part of posterior surface ulnaInnervationRadial Nerve

ActionAssists triceps in extending forearm; stabilizes elbow joint; may abduct ulna during protonation

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Muscles of Anterior Compartment of The Forearm

Superficial (first) layer and Intermediate (2 ND ) layerPronator Teres (PT)OriginUlnar head: coronoid processHumeral head: Medial epicondyle of humerus

InsertionMiddle convexity of lateral surface of radiusInnervationMedian nerve

ActionPronates & flexes forearm (at elbow)

Flexor carpi radialis (FCR)OriginMedial epicondyle of humerus (common flexor origin)

InsertionBase of 2nd metacarpal

InnervationMedian nerve

ActionFlexes & abducts hand (at wrist)

Palmaris longusOriginSame as FCR

InsertionDistal ½ of flexor retinaculum & apex of palmar aponeurosisInnervationMedian nerve

ActionFlexes hand (at wrist) & tenses palmar aponeurosis

Flexor Carpi Ulnaris (FCU)OriginHumeral head: medial epicondyle of humerusUlnar head: olecranon & posterior border (via aponeurosis)InsertionPisiform, hook of hamate, 5th metacarpal

InnervationUlnar nerve

ActionSame as palmar longus

Flexor digitorum superficialis (FDS)OriginHumeroulnar head and radial head: medial epicondyle(common flexor origin & coronoid process); superior ½ of anterior borderInsertionShafts of middle phalanges of medial 4 fingersInnervationMedian nerve

ActionFlexes middle phalanges at proximal interphalangeal joints of middle 4 fingers

Deep (3 rd ) Layer Flexor digitorum profundusOriginProximal ¾ of medial & anterior surfaces of ulna & interosseous membraneInsertionMedial part: bases of distal phalanges of 4th & 5th fingersLateral part: bases of distal phalanges of 2nd & 3rd fingersInnervationUlnar nerveActionFlexes distal phalanges 4 & 5

Flexor pollicis longus (FPL)OriginAnterior surface of radius & adjacent interosseous membraneInsertionBase of distal phalanx of thumbInnervationAnterior interosseous nerve, from median nerve

ActionFlexes distal phalanges of thumb

Pronator QuadratusOriginDistal ¼ of anterior surface of ulnaInsertionDistal ¼ of anterior surface of radiusInnervationSame as FPL

ActionPronates forearm, deep fibers bind radius & ulna together

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Muscles of Posterior Compartment of Forearm

Superficial LayerBrachioradialisOrigin Proximal 2/3 of supraepicondylar ridge

InsertionLateral surface of distal end of radius proximal to styloid process

InnervationRadial nerve

ActionWeak flexion of forearm, maximal when forearm is in midpronated position

Extensor Carpi radialis LongusOriginLateral supraepicondylar ridge of humerus

InsertionDorsal aspect of base of 2nd metacarpal

InnervationRadial nerve

ActionExtend & abduct hand at wrist joint

Extensor Carpi Radialis BrevisOriginLateral epicondyle of humerus (common extensor origin)

InsertionDorsal aspect of base of 3rd metacarpal

InnervationDeep branch of radial nerve

ActionActive during fist clenching (punch your lights out )

Extensor DigitorumOriginLateral epicondyle of humerus (common extensor origin)

InsertionExtensor expansions of medial 4 digits

InnervationPosterior interosseous nerve, continuation of deep branch of radial nerveActionExtends medial 4 fingers primarily at metacarpophalangeal joint

Extensor Digiti MinimiOriginLateral epicondyle of humerus (common extensor origin)

InsertionExtensor expansion of 5th digit

InnervationPosterior interosseous nerve, continuation of deep branch of radial nerveActionExtends 5th finger primarily at metacarpophalangeal joint

Extensor Carpi UlnarisOriginLateral epicondyle of humerus; posterior border of ulna via shared aponeurosisInsertionDorsal aspect of base of 5th metacarpal

InnervationPosterior interosseous nerve, continuation of deep branch of radial nerveActionExtends and adducts hand at wrist joint (also active during fist clenching…lights out again!)

Deep Layer Outcropping muscles of deep laye r SupinatorOriginLateral epicondyle of humerus’ radial collateral & anular ligaments; supinator fossa; crest of ulna

InsertionLateral, posterior, & anterior surfaces of proximal 3rd of radius

InnervationDeep branch of radial nerve

ActionSupinates forearm; rotates radius to turn palm anteriorly or superiorly (if elbow flexed)

Abductor pollicis longusOriginPosterior surface of proximal ½ of ulna, radius, interosseous membrane

InsertionBase of 1st metacarpal

InnervationPosterior interosseous nerve

ActionAbducts thumb & extends it at carpometacarpal joint

Extensor pollicis longusOriginPosterior surface of middle 3rd of ulna and interosseous membrane

InsertionDorsal aspect of base of distal phalanx of thumb

InnervationPosterior interosseous nerve

ActionExtends distal phalanx of thumb at interphalangeal joint

Extensor pollicis brevis OriginPosterior surface of distal 3rd of radius & interosseous membrane

InsertionDorsal aspect of base of proximal phalanx of thumb

InnervationPosterior interosseous nerve

ActionExtends proximal phalanx of thumb at metacarpophalangeal joint

Extensor indicisOriginPosterior surface of distal 3rd of ulna & interosseous membrane

InsertionExtensor expansion of 2nd finger

InnervationPosterior interosseous nerve

ActionExtends 2nd finger (enabling independent extension; helps extend hand at wrist

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Muscles of thoracic wallSerratus posterior superiorOriginNuchal ligament; spinous processes of C7-T3

InsertionSuperior borders of ribs 2-4

Innervation2nd-5th intercostal nerves

ActionElevate ribs

Serratus posterior inferiorOriginSpinous processes of T11-L2

InsertionInferior borders of 8th-12th ribs near their angles

Innervation9th- 11th intercostal nerves

ActionDepress ribs

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