 Superficial Skeletal Muscles Let's review each muscle to see its location and read about the action it performs. Oxypitalis draws back the scalp to raise the eyebrows. Trapezius, upper, elevates the scapula and extends the head and neck. Middle, retracts scapula medially. Lead lower, elevates scapula, upward rotation of the scapula and downward rotation of the scapula. Deltoid, abducts the arm, flexion and medial rotation, extension and lateral rotation. Infraspinatus, external rotation of the humerus, stabilizes the glenohumeral joint and part of the rotator cuff. Tera's major, assists in adduction of the arm, medial rotation of the arm and extension from a flexed position. Tera's minor, laterally rotates the arm, assists in adduction of the arm, stabilizes the glenohumeral joint and is part of the rotator cuff. Romboid major and minor, retracts the scapula and is located deep to the trapezius where it cannot be seen. Lattissimus dorsi, adduction of humerus, medial rotation of the humerus, extension from flexed position and downward rotation of the scapula. Triceps brachii, long, adducts the arm, extends at the shoulder and a little elbow flexion. Lateral, extends the forearm at the elbow and medial, extends the forearm at the elbow. Brachio radialis, acts as a synergist in forearm flexion. Extensor carpi radialis longus, extends the hand at the wrist, radially deviates the hand at the wrist, weakly flexes the forearm at the elbow and weakly supinates the forearm. Extensor carpi ulnaris, extends and adducts the hand at the wrist. Extensor digitorum, extends the foremedial digits, extends the wrist if the fingers are flexed, abducts the digits and is the most medial muscle in the posterior forearm. Gluteus medius, interior and lateral fibers abduct and medially rotate the thigh. Posterior fibers may laterally rotate the thigh and it stabilizes the pelvis and prevents free limb from sagging during gait. Gluteus maximus, powerful extensor of the hip, laterally rotates the thigh, upper fibers aid in abduction of the thigh, fibers of IT band stabilize a fully extended knee. Adductor magnus, adducts the thigh. Posterior fibers also extend and laterally rotate the thigh. Hamstrings, extend the thigh, flex the lower leg and include the biceps femoris, semi-tendinosis and semi-membranosis. Biceps femoris, flexor at the knee, laterally rotates the thigh if flexed at the knee and extends the hip. Semi-tendinosis, extends the hip, flexes the knee, medially rotates the tibia. Semi-membranosis, flexes the knee, extends the hip, medially rotates the tibia, pulls medial meniscus posterior during flexion. Gastrocnemius, planter flexes the ankle, knee flexion and stabilizes ankle and knee when standing. Solius, planter flexes the foot, fibularis longus, planter flexes and avert the foot. Calcennial tendon, insertion for the gastrocnemius and soleus muscles. Iliotibial tract, insertion for the tensor fasciae, lati and gluteus maximus. Deltoid, abducts the arm, flexion and medial rotation, extension and lateral rotation. Biceps brachii, flexes the forearm at the elbow, supinates forearm from neutral, stabilizes anterior aspect of the shoulder and flexes the shoulder. Brachialis, elbow flexion underneath the biceps brachii, pronator teres, pronates the forearm and weakly flexes the elbow. Brachioradialis, flexes the forearm at the elbow, pronates the forearm when supinated, supinates the forearm when pronated. Flexercarpi radialis, flexes the hand at the wrist, radially deviates the wrist and may assist to pronate the forearm. Palmaris longus, flexes the hand at the wrist. Pectoralis minor, depresses and downwardly rotates the scapula, assists in scapular protraction from a retracted position, stabilizes the scapula and is deep and cannot be seen. Pectoralis major, adducts humerus, medially rotates humerus, flexion of the arm from extension. Cerratus anterior, protracts the scapula, stabilizes scapula and assists in upward rotation. Intracostals, fix intracostal spaces during respiration and aid force inspiration by elevating the ribs. Rectus abdominis, flexes trunk, aids forced expiration, raises intra-abdominal pressure. External oblique, supports abdominal wall, assists forced expiration, assists in raising intra-abdominal pressure with muscles of opposite side it abducts and rotates the trunk. Internal oblique, supports abdominal wall, assists forced respiration, assists in raising intra-abdominal pressure with muscles of the other side it abducts and rotates the trunk. Fibers run medial to lateral underneath the external oblique. Transversus abdominis, supports abdominal wall, aids forced expiration and raising intra-abdominal pressure is deep and cannot be seen. Iliosus, flexes the torso and thigh with respect to each other. Pectaneous, flexes hip, adducts thigh, medially rotates the thigh. Rectus femoris, extends the knee and flexes the hip. Vastus lateralis, extends the knee and can abnormally displace the patella. Vastus medialis, extends the knee. Tensor fasciilate. Abduction and flexion at the hip, weak extension of knee joint, stabilizes the pelvis during walking, counters the pull of gluteus maximus on the iliotibial tract. Sartorius, flexes hip and knee, laterally rotates the thigh if flexed at the hip. Adductor longus, adducts thigh, flexes thigh, may laterally rotate thigh at the hip. Gracilis, adducts thigh, flexes knee and medially rotates the tibia. Tibialis anterior, strongest dorsiflector and inverts and educks the foot. Temporalis, elevates mandible and postfibers retract. Macedor, elevates mandible, enables forced closure of the mouth. Sternocleidomastoid, if contracted singularly, will rotate the head and neck to the opposite side. If contracted together, will cause anterior flexion of the head and neck. Frontalis, raises the eyebrows and wrinkles the forehead skin horizontally. Orbicularis oculi, powerfully closes the eye. Zygomaticus, zygomaticus minor, elevates the upper lip and zygomaticus major lifts and draws back the angles of the mouth as in smiling. Orbicularis aureus, closes the lips and protrudes the lips. Mentalis, elevates and protrudes the lower lip, wrinkles the skin over the chin. Depressor labiae inferioris, draws the lower lip inferiorly and laterally during mastication, used with mentalis for frowning. Buxinator, draws the corners of the mouth laterally and compresses the cheek, involved in the sucking action. Sternohioid, depresses hyoid bone and hence the larynx. Congratulations! You have completed this learning activity on the superficial skeletal muscles.