Learn: Anatomy: Major Skeletal Muscle Actions, Origins, and Insertions

Action: Acting together (bilateral), flex cervical portion of vertebral column and head; acting singly (unilateral), laterally flex and rotate head to side opposite contracting muscle

Sternocleidomastoid

Action: Depends on active region and state of other muscles; may (1) elevate, retract, depress, or rotate scapula upward, (2) elevate clavicle, or (3) extend neck

Trapezius

Action: Extends, adducts, and medially rotates arm at shoulder joint; draws arm inferiorly and posteriorly

Latissimus dorsi

Action: As a whole, adducts and medially rotates arm at shoulder joint; clavicular head alone flexes arm at shoulder joint

Pectoralis major

Action: Flexes vertebral column, especially lumbar portion, and compresses abdomen to aid in defecation, urination, forced expiration, and parturition (childbirth)

Rectus abdominis

Action: Middle fibers abduct arm at shoulder joint; anterior fibers flex and medially rotate arm at shoulder joint; posterior fibers extend and laterally rotate arm at shoulder joint

Deltoid

Action: Flexes forearm at elbow joint, supinates forearm at radioulnar joints, and flexes arm at shoulder joint

Biceps brachii

Action: Extends forearm at elbow joint and extends arm at shoulder joint

Triceps brachii

Action: All four heads (of the quadriceps) extend leg at knee joint; rectus femoris muscle acting alone also flexes thigh at hip joint

Rectus femoris, Vastus medialis, Vastus lateralis, & Vastus intermedius

Action: (The hamstrings) flex leg at knee joint and extend thigh at hip joint

Biceps femoris, Semitendinosus, & Semimembranosus

Action: Plantar flexes foot at ankle joint and leg at knee joint

Gastrocnemius

Origin: Sternum and clavicle

Insertion: Mastoid process of temporal bone

Sternocleidomastoid

Origin: Occipital bone, ligamentum nuchae, and spinous processes of thoracic vertebrae

Insertion: Clavicle and scapula (acromion and scapular spine)

Trapezius

Origin: Spines of inferior six thoracic vertebrae, lumbar vertebrae, crests of sacrum and ilium, inferior four ribs, inferior angle of scapula

Insertion: Intertubercular groove of humerus

Latissimus dorsi

Origin: Clavicle (clavicular head), sternum, and cartilages of second to sixth ribs (sternocostal head)

Insertion: Greater tubercle and intertubercular groove of humerus

Pectoralis major

Origin: Pubic crest and pubic symphysis

Insertion: Cartilage of fifth to seventh ribs and xiphoid process

Rectus abdominis

Origin: (1) Anterior fibers: acromial extremity of clavicle, (2) Middle fibers: acromion of scapula, (3) Posterior fibers: spine of scapula

Insertion: Deltoid tuberosity of humerus

Deltoid

Origin: (1) Long head: supraglenoid tubercle of the scapula, (2) Short head: coracoid process of scapula

Insertion: Radial tuberosity and bicipital aponeurosis

Biceps brachii

Origin: (1) Long head: projection inferior to glenoid cavity of scapula, (2) Lateral head: lateral and posterior surface of humerus superior to radial groove, (3) Medial head: entire posterior surface of humerus inferior to a groove for the radial nerve

Insertion: Olecranon of ulna

Triceps brachii

Origin: Anterior inferior iliac spine

Insertion: Patella via quadriceps tendon and then tibial tuberosity via patellar ligament

Rectus femoris

Origin: Linea aspera of femur

Insertion: Patella via quadriceps tendon and then tibial tuberosity via patellar ligament

Vastus medialis

Origin: Greater trochanter and linea aspera of femur

Insertion: Patella via quadriceps tendon and then tibial tuberosity via patellar ligament

Vastus lateralis

Origin: Anterior and lateral surfaces of body of femur

Insertion: Patella via quadriceps tendon and then tibial tuberosity via patellar ligament

Vastus intermedius

Origin: Long head arises from ischial tuberosity; short head arises from linea aspera of femur

Insertion: Head of fibula and lateral condyle of tibia

Biceps femoris

Origin: Ischial tuberosity

Insertion: Proximal part of medial surface of shaft of tibia

Semitendinosus

Origin: Ischial tuberosity

Insertion: Medial condyle of tibia

Semimembranosus

Origin: Lateral and medial condyles of femur and capsule of knee

Insertion: Calcaneus by way of calcaneal (Achilles) tendon

Gastrocnemius