How can we help?

You can also find more resources in our Help Center.

42 terms

Muscle Action

STUDY
PLAY
Masseter
Elevation of mandible, minor role in protraction, retraction, and lateral and medial excursion
Temporalis
Elevation retraction, lateral and medial excursion of madible
Scalenes
Unilateral contraction causes ipsilateral flexion or contralateral rotation. Bilateral contraction flexes neck
Sternocleidomastoid
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
Diaphragm
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
Rhomboids
Retracts scapula and braces shoulder; fixes scapula during arm movement (prime antagonist)
Trapezius
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
Brachioradialis
Flexes elbow
Deltoid
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
Subscapularis
Modulates action of deltoid, preventing humeral head from sliding upward as arm is abducted; rotates humerus medially
Supinator
Supinate forearm
Supraspinatus
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
Illiacus
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
Gracilis
Flexes and medially rotates tibia at knee
Sartorius
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
Gastrocnemius
Plantar flexes foot, flexes knee; active in walking, running and jumping
Illiopsoas
Strongest of the hip flexors (rectus femoris, sartorius, and tensor fasciae latae), iliopsoas is important for standing, walking, and running.