Muscles associated with the shoulders and upper limbs can be divided into four groups: (1) muscles that position the pectoral girdle, (2) muscles that move the arm, (3) muscles that move the forearm and hand, and (4) muscles that move the hand and fingers.

Muscles That Position the Pectoral Girdle

The large, superficial trapezius muscles cover the back and portions of the neck, reaching to the base of the skull. These muscles originate along the midline of the neck and back and insert on the clavicles and the scapular spines (Figures 11-14 and 11-15a). The trapezius muscles are innervated by more than one nerve (Table 11-11), and specific regions can be made to contract independently. As a result, their actions are quite varied.

Removing the trapezius muscle reveals the rhomboideus and levator scapulae muscles (Figure 11-15a). These muscles are attached to the dorsal surfaces of the cervical and thoracic vertebrae. They insert along the vertebral border of each scapula, between the superior and inferior angles. Contraction of a rhomboideus muscle adducts (retracts) the scapula on that side. The levator scapulae muscle, as its name implies, elevates the scapula.

On the chest, the serratus anterior muscle originates along the anterior surfaces of several ribs (Figures 11-3 and 11-15a, b). This fan-shaped muscle inserts along the anterior margin of the vertebral border of the scapula. When the serratus anterior muscle contracts, it abducts (protracts) the scapula and swings the shoulder anteriorly.

Two other deep chest muscles arise along the ventral surfaces of the ribs on either side. The subclavius muscle inserts on the inferior border of the clavicle (Figure 11-15b). When it contracts, it depresses and protracts the scapular end of the clavicle. Because ligaments connect this end to the shoulder joint and scapula, those structures move as well. The pectoralis minor muscle attaches to the coracoid process of the scapula. The contraction of this muscle generally complements that of the subclavius muscle.

Muscles That Move the Arm

The muscles that move the arm (Figures 11-14 and 11-16) are easiest to remember when grouped by their actions at the shoulder joint (Table 11-12). The deltoid muscle is the major abductor, but the supraspinatus  muscle assists at the start of this movement. The subscapularis and teres major muscles produce medial rotation at the shoulder, whereas the infraspinatus and the teres minor muscles produce lateral rotation. All these muscles originate on the scapula. The small coracobrachialis  muscle is the only muscle attached to the scapula that produces flexion and adduction at the shoulder.

The pectoralis major muscle extends between the anterior portion of the chest and the crest of the greater tubercle of the humerus. The latissimus dorsi muscle extends between the thoracic vertebrae at the posterior midline and the intertubercolar groove of the humerus (Figure 11-16b). The pectoralis major muscle produces flexion at the shoulder joint, and the latissimus dorsi muscle produces extension. These two muscles can also work together to produce adduction and medial rotation of the humerus at the shoulder.

Collectively, the supraspinatus, infraspinatus, subscapularis, and teres minor muscles and their associated tendons form the rotator cuff, a common site of sports injuries.

Muscles That Move the Forearm and Hand

Although most of the muscles that insert on the forearm and hand originate on the humerus, the biceps brachii and triceps brachii muscles are noteworthy exceptions. The biceps brachii muscle and the long head of the triceps brachii muscle originate on the scapula and insert on the bones of the forearm (Figure 11-17). The triceps brachii muscle inserts on the olecranon. Contraction of the triceps brachii muscle extends the elbow, as when you do push-ups. The biceps brachii muscle inserts on the radial tuberosity, a roughened area on the anterior surface of the radius.  Contraction of the biceps brachii muscle flexes the elbow and supinates the forearm. With the forearm pronated (palm facing back), the biceps brachii muscle cannot function effectively. As a result, you are strongest when you flex your elbow with a supinated forearm; the biceps brachii muscle then makes a prominent bulge.

More muscles are shown in Figure 11-17 and listed in Table 11-13. The brachialis and brachioradialis muscles flex the elbow and are opposed by the anconeus muscle and the triceps brachii muscle, respectively.

The flexor carpi ulnaris, flexor carpi radialis, and palmaris longus muscles are superficial muscles that work together to produce flexion of the wrist. The flexor carpi radialis muscle flexes and abducts, and the flexor carpi ulnaris muscle flexes and adducts. Pitcher's arm is an inflammation at the origins of the flexor carpi muscles at the medial epicondyle of the humerus. This condition results from forcibly flexing the wrist just before releasing a baseball.

The extensor carpi radialis muscles and the extensor carpi ulnaris muscle have a similar relationship to that between the flexor carpi muscles. The extensor carpi radialis muscles produce extension and abduction, whereas the extensor carpi ulnaris muscle produces extension and adduction.

The pronator teres and supinator muscles originate on both the humerus and ulna. These muscles rotate the radius without either flexing or extending the elbow. The pronator quadratus muscle originate on the ulna and assists the pronator teres muscle in opposing the actions of the supinator or biceps brachii muscles. The muscles involved in pronation and supination are shown in Figure 11-18. During pronation, the tendon of the biceps brachii muscle rotates with the radius. As a result, this muscle cannot assist in flexion of the elbow when the forearm is pronated.

As you study the muscles included in Table 11-13, notice that, in general, the extensor muscles lie along the posterior and lateral surfaces of the arm, whereas the flexors are on the anterior and medial surfaces.

Muscles That Move the Hand and Fingers

Several superficial and deep muscles of the forearm flex and extend the finger joints (Figure 11-18 and Table 11-14). These muscles stop before reaching the wrist, and only their tendons cross the articulation. The muscles are relatively large, and keeping them clear of the joints ensures maximum mobility at both the wrist and hand. The tendons that cross the dorsal and ventral surfaces of the wrist pass through tendon sheaths, elongate bursae that reduce friction.

The muscles of the forearm provide strength and crude control of the hand and fingers. These muscles are known as the extrinsic muscles of the hand. Fine control of the hand involves small intrinsic muscles, which originate on the carpal and metacarpal bones. No muscles originate on the phalanges, and only tendons extend across the distal joints of the fingers. The intrinsic muscles of the hand are detailed in Figure 11-19 and Table 11-15.

The fascia of the forearm thickens on the posterior surface of the wrist, forming the extensor retinaculum, a wide band of connective tissue. The extensor retinaculum holds the tendons of the extensor muscles in place. On the anterior surface, the fascia also thickens to form another wide band of connective tissue, the flexor retinaculum, which stabilizes the tendons of the flexor muscles. Inflammation of the retinacula and tendon sheaths can restrict movement and irritate the median nerve, a mixed (sensory and motor) nerve that innervates the hand. This condition, known as carpal tunnel syndrome, causes chronic pain. 

Which muscle are you using when you shrug your shoulders?

Baseball pitchers sometimes suffer from rotator cuff injuries. Which muscles are involved in this type of injury?

Injury to the flexor carpi ulnaris muscle would impair which two movements?

Sports Injuries Exercise carries risks due to the stresses placed on muscles, joints, and connective tissues. Many of us participate in exercise programs and sports on a regular basis. More than 30 million people jog in the United States, and millions more participate in various amateur and professional sports. As a result, sports injuries are very common, and sports medicine has become an active area of professional and academic research interest. Sports Injuries

Carpal Tunnel Syndrome Tenosynovitis is the inflammation of a tendon sheath. Carpal tunnel syndrome results from tenosynovitis of the synovial tendon sheath surrounding the flexor tendons of the palm. The inflammation leads to compression of the median nerve. Symptoms include pain, especially on palmar flexion, a tingling sensation or numbness on the palm, and weakness in the abductor pollicis brevis. This common condition often strikes persons engaged in repetitive hand movements, such as typing, working at a computer keyboard, or playing the piano. Treatment involves the administration of anti-inflammatory drugs such as aspirin, the injection of anti-inflammatory agents such as glucocorticoids (steroid hormones produced by the adrenal cortex), and the use of a splint to prevent wrist flexion and to stabilize the region. Carpal tunnel syndrome is an example of a cumulative trauma disorder, or overuse syndrome. These disorders are caused by repetitive movements of the arms, hands, and fingers. Such musculoskeletal problems now account for over 50 percent of all work-related injuries in the United States.