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Elevation of mandible, minor role in protraction, retraction, and lateral and medial excursion


Elevation retraction, lateral and medial excursion of madible


Unilateral contraction causes ipsilateral flexion or contralateral rotation. Bilateral contraction flexes neck


Unilateral action tilts head slightly upward and toward the opposite side, Rotating left and right Bilateral action draws head straight forward and down, when eating or reading


Prime mover of inspiration; contracts in preparation for sneezing, and etc. 2/3 of air intake

Internal intercostals

In inspiration, part aids in elevating the ribs and expanding the thoracic cavity. In expiration, depresses and retracts the ribs, compressing the thoracic cavity.

Erector spinae

Extension and lateral flexion of vertebral column; the longissimus capitis also produces ipsilateral rotation of the head.

Latissimus dorsi

Adducts and medially rotates humerus; extends the shoulder joint as in pulling on the oars of rowboat; produces backward swing of arm; pulls body forward and upward, as in climbing

Levator Scapulae

Elevates scapula if cervical vertebrae are fixed; flexes neck laterally if scapular is fixed

Pectoralis major

Flexes, adducts, and medially rotates humerus, as in climbing or hugging; aids in deep inspiration

Pectoralis minor

Depresses the point of the shoulder, drawing the scapula inferior and medial, towards the thorax, and throwing its inferior angle posteriorly.

External intercostals

When scalenes fix rib 1, external intercostals elevate and protract ribs 2-12, expanding the thoracic cavity and creating a partial vacuum causing inflow of air; exercise a braking action during expiration so that expiration is not overly abrupt

Quadratus lumborum

Aids respiration by fixing rib 12 and stabilizing inferior attachments of diaphragm. Unilateral contraction causes ipsilateral flexion of lumbar vertebral colum; bilateral contraction extends lumbar vertebral colum


Retracts scapula and braces shoulder; fixes scapula during arm movement (prime antagonist)


Stabilizes scapula and shoulder during arm movement; elevates and depresses apex of shoulder; acts with other muscles to rotate and retract scapula

Biceps brachii

Rapid or forceful supination; synergist in elbow flexion; slight shoulder flexion; tendon of long head stabilizes shoulder by holding humeral head against glenoid cavity


Flexes elbow


Anterior fibers flex and medially rotate arm; lateral fibers abduct arm; posterior fibers extend and laterally rotate arm

Extensor carpi radialis (longus)

Extends wrist

Extensor carpi radialis brevis

Extends wrist

Palmaris longus

Anchors skin and fascia of palmar region; resists shearing forces when stress is applied to skin by such action as climbing and tool use. Weekely developed and sometimes absent

Pronator teres

Assists pronator quadratus in pronation, but only in rapid or forceful action; weakly flexes elbow


Modulates action of deltoid, preventing humeral head from sliding upward as arm is abducted; rotates humerus medially


Supinate forearm


Aids deltoid in abduction of arm; resists downward slippage of humeral head when arm is relaxed or when carrying weight

Teres minor

Modulates action of deltoid, preventing humeral head from sliding upward as arm is abducted; rotates humerus laterally

Triceps Brachii

Extends elbow; long head extends and adducts humerus

External oblique

Supports abdominal viscera against pull of gravity; stabilizes vertebral column during heavy lifting; maintains posture; compresses abdominal organs, thus aiding in forceful expiration of breath and in expulsion of abdominopelvic contents during childbirth, urination, defecation, and vomiting, unilateral contraction causes contralateral rotation of waist

Rectus abdominis

Flexes lumbar region of vertebral column, producing forward bending at the waist


Flexes thigh at hip when trunk is fixed; flexes trunk at hip when thigh is fixed, as in bending forward in a chair or sitting up in bed; balances trunk during sitting

Psoas major

Flexes thigh at hip when trunk is fixed; flexes trunk at hip when thigh is fixed, as in bending forward in a chair or sitting up in bed; balances trunk during sitting

Levator ani

Compresses anal canal and reinforces external anal and urethral sphincters; supports uterus and other pelvic viscera; aids in the falling away of the feces; vertical movements affect pressure difference between abdominal and thoracic cavities and thus aid in deep breathing

Adductor brevis

Adducts thigh

Adductor longus

Adducts and medially rotates thigh; flexes thigh at hip

Adductor Magnus

Adducts and medially rotates thigh; extends thigh at hip


Flexes and medially rotates tibia at knee


Aids in knee and hip flexion, as in sitting or climbing; abducts and laterally rotates thigh

Tensor fasciae latae

Extends knee laterally rotates tibia, aids in abduction and medial rotation of femur; during standing, steadies pelvis on femoral head and stedies femoral condyles on tibia

Gluteus maximus

Extend thigh at hip as in stair climbing (rising to next step) or running and walking (backswing of limb); abducts thigh; elevates trunk after stooping; prevents trunk from pitching forward during walking and running; helps stabilize femur on tibia

Biceps femoris

Flexes knee; extends hip; elevates trunk from stooping posture; laterally rotates tibia on femur when knee is fixed; laterally rotates femur when hip is extended; counteracts forward bending at hips


Plantar flexes foot, flexes knee; active in walking, running and jumping


Strongest of the hip flexors (rectus femoris, sartorius, and tensor fasciae latae), iliopsoas is important for standing, walking, and running.

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