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Sternocleidomastoid: breastbone-clavicle-mastoid process
Action: prime mover of active head flexion; individually each muscle rotates head towards the shoulder on opposite side
- O: manubrium of sternum and medial portion of clavicle
- I: mastoid process and superior nuchal line of occipital bone
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scalenus: uneven
anterior, middle, posterior
Action: elevates first two ribs (respiration); flexes and rotates neck
- O: transverse process of cervicle vertebrae
- I: anterolaterally (front & side) on first two ribs
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splenius:
capitus (head), cervicis (neck)
Action: act as a group to extend of hyperextend the head; when one side, head is rotated and bent laterally towards same side
- O: nuchal ligament and spinous processes of C7-T6 vertebrae
- I: mastoid process and transverse processes of C2-C4 vertebrae
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Erector spinae:
Action: helps control action of bending forward; act as powerful extensors to return to erect position; during full flexion (fingers to floor) erector spinae are relaxed
- Iliocostalis
- Longissimus
- Spinalis
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Iliocoastalis: rib
lumborum, thoracis, cervicis
Action: extend vertebral column; acting on one side, bends vertebral column to same side
- O: iliac crest (lumborum); inferior 6 ribs (thoracis); ribs 3-6 (cervicis)
- I: angles of ribs (lumborum, thoracis); transverse processes of cervical vertebrae C6-C4 (cervicis)
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Longissimus:
thoracis, cervicis, capitis
Action: thoracis and cervicis act together to extend vertebral column, or on one side to laterally bend; capitis extends head and turns the face toward same side
- O: transverse process of lumbar through cervical vertebrae
- I: transverse processes of thoracic or cervical vertebrae and to ribs superior to origin; capitis inserts to mastoid process
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Spinalis:
thoracic, cervicis
Action: extends vertebral column
- O: spines of upper lumbar and lower thoracic vertebrae
- I: spines of upper thoracic and cervical vertebrae
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Semispinalis:
thoracis, cervicis, capitis
Action: extends vertebral column and head and rotates them to opposite side; acts synergistically with sternocleidomastoid muscles of opposite side
- O: transverse processes of C7-T12
- I: occipital bone (capitis); spinous processes of cervical vertebrae (cervicis); thoracic vertebrae T1-T4 (thoracis)
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Quadratus lumborum: foursided-lumbar region
Action: flexes vertebral column laterally when acting separately; when paired, lumbar spines is extended and 12th rib is fixed; maintains upright posture
- O: iliac crest and lumbar fascia
- I: transverse processes of upper lumbar vertebrae and lower margin of 12th rib
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External intercostals: toward the outside- between rib
Action: pulls ribs toward one another to elevate rib cage; aids in respiration; synergist to diaphragm
- O: inferior border of rib above
- I: superior border of rib below
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Internal intercostals: toward the inside- between ribs
Action: aids in drawing ribs together and forced respiration; antagonist to external intercostals
- O: superior border of rib below
- I: inferior border of rib above
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Diaphragm: across-partition
Action: prime mover of inspiration
- O: inferior, internal surface of rib cage and sternum, costal cartilages of last six ribs and lumbar vertebrae
- I: central tendon
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Rectus abdominus: straight-abdomen
Action: flex and rotate lumbar region of vertebral column; fix and depress ribs; stabilize pelvis during walking
- O: pubic crest and symphysis
- I: xiphoid process and costal cartilages of ribs 5-7
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External oblique: toward outside- running at an angle
Action: pair contracts to aid in flexion of vertebral column; individually aid back muscles in trunk rotation/ lateral flexion
- O: by fleshy strips from outer surfaces of lower eight ribs
- I: most fibers insert anteriorly into linea alba, some onto pubic crest, pubic tubercle, and iliac crest
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Internal oblique: deep- running at an angle
Action: flexing vertebral column; aid muscles of back in trunk rotation and lateral flexion
- O: lumbar fascia, iliac crest, and inguinal ligament
- I: linea alba, pubic crest, last 3-4 ribs, and costal margin
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Transversus abdominus: running straight across- abdomen
Action: compresses abdominal contents
- O: inguinal ligament, lumbar fascia, cartilages of last 6 ribs; iliac crest
- I: linea alba, pubic crest
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Pectoral minor: chest- lesser
Action: draws scapula forward and downward with ribs fixed; with scapula fixed, draws rib cage superiorly
- O: anterior surfaces of ribs 3-5 or 2-4
- I: coracoid process of scapula
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Serratus anterior: saw
Action: prime mover to protract and hold scapula against chest wall; rotates scapula to move laterally and upward; important role in abduction and raising of arm
- O: a series of muscle slips from ribs 1-8 (or 9)
- I: entire anterior surface of vertebral border of scapula
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Subclavius: beneath-clavicle
Action: helps stabilize and depress pectoral girdle
- O: costal cartilage of rib 1
- I: groove on inferior surface of clavicle
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Trapezius: irregular four-sided figure
Action: stabilizes, raises, retracts, and rotates scapula; middle fibers retract (adduct) scapula; superior fibers elevate or extend head when scapula is fixed; inferior fibers depress
- O: occipital bone, nuchal ligament, and spines of C7 and all thoracic vertebrae
- I: a continuous insertion along acromion and spine of scapula and lateral third of clavicle
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Levator scapulae: raises- scapula
Action: elevates adducts scapula in concert with superior fibers of trapezius
- O: transverse processes of C1-C4
- I: medial border of scapula, superior to the spine
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Rhomboids: diamond shaped
major, minor
Action: retracts scapula- squaring shoulders; stabilizes scapula
- O: spinous processes of C7 and T1 (minor); spinous processes of T2-T5 (major)
- I: medial border of scapula
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Pectoralis major: chest- larger
Action: prime mover of arm flexion; rotates arm medially; adducts arm against resistance; pulls ribcage upward to aid in forced respiration
- O: sternal end of clavicle, sternum cartilage of ribs 1-6 (or 7), and aponeurosis of external oblique muscle
- I: fibers converge to insert by a short tendon into intertubercular groove of humerus
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Latissimus dorsi: widest- back
Action: prime mover of arm extension; arm adductor; medially rotates arm at shoulder; depresses scapula
- O: indirect attachment via lumbodorsal fascia into spines of lower six thoracic vertebrae, lumbar vertebrae, lower ribs 3-4, and iliac crest
- I: spirales around teres major to insert in floor of intertubercular groove of humerus
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Deltoid: triangular
Action: prime mover of arm abduction; when all fibers are active- antagonist to pectoralis major and latissimus dorsi; when anterior fibers are active acts in flexion and medial rotation of humerus therefore synergist to pectoralis major; posterior fibers effects extension and lateral rotation of arm
- O: embraces insertion of trapezius: lateral third of clavicle; acromium and spine of scapula
- I: deltoid tuberosity of humerus
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Subscapularis: under- scapula
Action: chief medial rotator of humerus; stabilizes shoulder joint
- O: subscapular fossa of scapula
- I: lesser tubercle of humerus
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Supraspinatus: above- spine
Action: stabilizes shoulder joint; assists in abduction of arm
- O: supraspinous fossa of scapula
- I: superior part of greater tubercle of humerus
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Infraspinatous: below- spine
Action: stabilizes shoulder joint; rotates humerus laterally
- O: infraspinous fossa of scapula
- I: greater tubercle of humerus
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Teres minor: round- lesser
Action: stabilizes shoulder joint; rotates humerus laterally; adducts arm
- O: lateral border of dorsal scapular surface
- I: greater tubercle of humerus
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Teres major: round- greater
Action: posteromedially extends, medially rotates, and adducts humerus; synergist of latissimus dorsi
- O: posterior surface of scapula at inferior angle
- I : intertubercular groove of humerus; insertion tendon fused with that of latissumus dorsi
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Coracobrachialis: arm
Action: flexion and adduction of the humerus; synergist of pectoralis major
- O: coracoid process of scapula
- I: medial surface of humerus shaft
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