Skeletal Muscle Locations, Attachments, & Actions - Massage and Bodywork Licensing Examination Mblex

1. What is the primary action of the sternocleidomastoid when both sides contract?

   Cervical flexion (neck flexion). Bilateral contraction of the sternocleidomastoid pulls the head forward by drawing the mastoid process toward the sternum and clavicle.

2. What is the primary action of the serratus anterior on the scapula?

   Scapular protraction and upward rotation. The serratus anterior originates on the ribs and inserts on the medial scapular border, pushing the scapula forward and upward for reaching motions.

3. What is the primary action of the brachialis muscle at the elbow?

   Primary elbow flexor. Brachialis lies deep to the biceps, attaching from humerus to ulna, providing strong flexion independent of forearm position.

4. What is the primary action of the levator scapulae on the scapula?

   Scapular elevation and downward rotation. Levator scapulae runs from cervical vertebrae to the superior scapular angle, lifting the scapula and rotating it downward to assist neck movements.

5. What is the primary action of the triceps brachii at the elbow?

   Elbow extension. Triceps brachii's three heads originate on the humerus and scapula, inserting on the ulna to straighten the elbow against resistance.

6. What is the primary action of the rhomboids (major and minor) on the scapula?

   Scapular retraction and downward rotation. Rhomboids connect the thoracic vertebrae to the medial scapula, drawing it toward the spine while rotating it downward for stability in pulling actions.

7. What is the primary action of the supraspinatus muscle at the shoulder?

   Initiates shoulder abduction and stabilizes the humeral head. Supraspinatus, part of the rotator cuff, compresses the humeral head in the glenoid while starting abduction to prevent impingement.

8. What is the primary action of the middle trapezius on the scapula?

   Scapular retraction (adduction). Middle trapezius fibers connect the thoracic vertebrae to the scapular spine, enabling pulling of the scapulae toward the midline for posture maintenance.

9. What is the primary action of the teres major muscle at the shoulder?

   Shoulder adduction and medial rotation (assists extension). Teres major connects the scapula to the humerus, aiding in drawing the arm down and inward while supporting backward movement.

10. What is the primary action of the subscapularis muscle at the shoulder?

    Medial (internal) rotation of the humerus. Subscapularis fills the subscapular fossa and inserts on the lesser tubercle, providing internal rotation and anterior shoulder stability.

11. What is the primary action of the gastrocnemius muscle at the ankle joint?

    Plantarflexion of the ankle (assists knee flexion). Gastrocnemius crosses the knee and ankle, contracting to point the toes downward while aiding in bending the knee for propulsion in walking.

12. What is the primary action of the latissimus dorsi at the shoulder?

    Shoulder extension, adduction, and medial rotation. Latissimus dorsi's broad origin from the thoracolumbar area to humeral insertion allows backward, inward, and rotational pull for activities like rowing.

13. What is the primary action of the pronator teres on the forearm?

    Forearm pronation (assists elbow flexion). Pronator teres originates on the humerus and ulna, inserting on the radius to rotate it inward, with secondary support for elbow bending.

14. What is the primary action of the biceps brachii at the elbow and forearm?

    Elbow flexion and forearm supination. Biceps brachii crosses the elbow and radioulnar joints, contracting to bend the elbow and rotate the palm upward for tasks like lifting.

15. What is the primary action of the infraspinatus muscle at the shoulder?

    Lateral (external) rotation of the humerus. Infraspinatus originates in the infraspinous fossa and inserts on the greater tubercle, enabling outward rotation to stabilize the shoulder joint.

16. What is the primary action of the supinator muscle on the forearm?

    Forearm supination. Supinator wraps around the radius from the humerus and ulna, contracting to rotate the forearm outward for actions like turning a screwdriver.

17. What is the primary action of the masseter muscle at the temporomandibular joint?

    Elevation of the mandible (jaw closing). The masseter's attachment from the zygomatic arch to the mandible enables powerful upward pull for jaw closure during mastication.

18. What is the primary action of the upper trapezius on the scapula?

    Scapular elevation and upward rotation. The upper trapezius fibers run from the occiput and cervical vertebrae to the acromion, facilitating lifting and rotating the scapula upward for overhead movements.

19. What is the primary action of the lower trapezius on the scapula?

    Scapular depression and upward rotation. Lower trapezius fibers from the lower thoracic vertebrae to the scapular spine depress and rotate the scapula upward to support arm elevation.

20. What is the primary action of the teres minor muscle at the shoulder?

    Lateral rotation of the humerus. Teres minor, a rotator cuff muscle, attaches from the scapula to the humerus, facilitating external rotation for shoulder stability during lifts.

21. What is the primary action of the deltoid muscle as a whole at the shoulder?

    Shoulder abduction (especially midrange). The deltoid's middle fibers abduct the arm by lifting the humerus laterally, most effective between 15-90 degrees due to optimal leverage.

22. What is the primary action of the temporalis muscle on the mandible?

    Elevation and retraction of the mandible. The temporalis originates on the temporal bone and inserts on the coronoid process, allowing it to lift and pull back the jaw for chewing.

23. What is the primary action of the pectoralis major at the glenohumeral joint?

    Shoulder adduction and medial rotation. Pectoralis major spans from the chest to the humerus, pulling the arm toward the body and rotating it inward for actions like hugging or climbing.

24. What is the primary action of the sternocleidomastoid when one side contracts?

    Contralateral head rotation with ipsilateral lateral flexion. Unilateral sternocleidomastoid contraction rotates the head away from the side while bending it toward the contracting muscle due to its oblique fiber orientation.

25. Identify the muscle that originates on the iliac crest and inserts on the femur to abduct the hip: what is it?

    Gluteus medius. Gluteus medius's position on the lateral pelvis allows it to pull the femur away from the midline, stabilizing the hip during walking.

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