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2-7-6. Muscles of the Pectoral Girdle and Upper Limbs

Learning Objectives

  • Identify the muscles of the pectoral girdle and upper limbs
  • Identify the movement and function of the pectoral girdle and upper limbs

Muscles of the shoulder and upper limb can be divided into four groups: muscles that stabilize and position the pectoral girdle, muscles that move the arm, muscles that move the forearm, and muscles that move the wrists, hands, and fingers. The pectoral girdle, or shoulder girdle, consists of the lateral ends of the clavicle and scapula, along with the proximal end of the humerus, and the muscles covering these three bones to stabilize the shoulder joint. The girdle creates a base from which the head of the humerus, in its ball-and-socket joint with the glenoid fossa of the scapula, can move the arm in multiple directions.

Muscles That Position the Pectoral Girdle

Muscles that position the pectoral girdle are located either on the anterior thorax or on the posterior thorax (Figure 1 and Table 1). The anterior muscles include the subclavius, pectoralis minor, and serratus anterior. The posterior muscles include the trapezius, rhomboid major, and rhomboid minor. When the rhomboids are contracted, your scapula moves medially, which can pull the shoulder and upper limb posteriorly.

Muscles That Position the Pectoral Girdle

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Figure 1: The muscles that stabilize the pectoral girdle make it a steady base on which other muscles can move the arm. Note that the pectoralis major and deltoid, which move the humerus, are cut here to show the deeper positioning muscles. (Click on the image to enlarge)

Muscles That Move the Humerus

Similar to the muscles that position the pectoral girdle, muscles that cross the shoulder joint and move the humerus bone of the arm include both axial and scapular muscles (Figure 2 and Figure 3). The two axial muscles are the pectoralis major and the latissimus dorsi. The pectoralis major is thick and fan-shaped, covering much of the superior portion of the anterior thorax. The broad, triangular latissimus dorsi is located on the inferior part of the back, where it inserts into a thick connective tissue shealth called an aponeurosis.

Muscles That Move the Humerus

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Figure 2: (a, c) The muscles that move the humerus anteriorly are generally located on the anterior side of the body and originate from the sternum (e.g., pectoralis major) or the anterior side of the scapula (e.g., subscapularis). (b) The muscles that move the humerus superiorly generally originate from the superior surfaces of the scapula and/or the clavicle (e.g., deltoids). The muscles that move the humerus inferiorly generally originate from middle or lower back (e.g., latissiumus dorsi). (d) The muscles that move the humerus posteriorly are generally located on the posterior side of the body and insert into the scapula (e.g., infraspinatus). (Click on the image to enlarge)

Muscles That Move the Humerus

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Figure 3. (Click on the image to enlarge)

The rest of the shoulder muscles originate on the scapula. The anatomical and ligamental structure of the shoulder joint and the arrangements of the muscles covering it, allows the arm to carry out different types of movements. The deltoid, the thick muscle that creates the rounded lines of the shoulder is the major abductor of the arm, but it also facilitates flexing and medial rotation, as well as extension and lateral rotation. The subscapularis originates on the anterior scapula and medially rotates the arm. Named for their locations, the supraspinatus (superior to the spine of the scapula) and the infraspinatus (inferior to the spine of the scapula) abduct the arm, and laterally rotate the arm, respectively. The thick and flat teres major is inferior to the teres minor and extends the arm, and assists in adduction and medial rotation of it. The long teres minor laterally rotates and extends the arm. Finally, the coracobrachialis flexes and adducts the arm.

The tendons of the deep subscapularis, supraspinatus, infraspinatus, and teres minor connect the scapula to the humerus, forming the rotator cuff (musculotendinous cuff), the circle of tendons around the shoulder joint. When baseball pitchers undergo shoulder surgery it is usually on the rotator cuff, which becomes pinched and inflamed, and may tear away from the bone due to the repetitive motion of bring the arm overhead to throw a fast pitch.

Muscles That Move the Forearm

The forearm, made of the radius and ulna bones, has four main types of action at the hinge of the elbow joint: flexion, extension, pronation, and supination. The forearm flexors include the biceps brachii, brachialis, and brachioradialis. The extensors are the triceps brachii and anconeus. The pronators are the pronator teres and the pronator quadratus, and the supinator is the only one that turns the forearm anteriorly. When the forearm faces anteriorly, it is supinated. When the forearm faces posteriorly, it is pronated.

The biceps brachii, brachialis, and brachioradialis flex the forearm. The two-headed biceps brachii crosses the shoulder and elbow joints to flex the forearm, also taking part in supinating the forearm at the radioulnar joints and flexing the arm at the shoulder joint. Deep to the biceps brachii, the brachialis provides additional power in flexing the forearm. Finally, the brachioradialis can flex the forearm quickly or help lift a load slowly. These muscles and their associated blood vessels and nerves form the anterior compartment of the arm (anterior flexor compartment of the arm) (Figure 4 and Figure 5).

Muscles That Move the Forearm

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Figure 4: The muscles originating in the upper arm flex, extend, pronate, and supinate the forearm. The muscles originating in the forearm move the wrists, hands, and fingers. (Click on the image to enlarge)

Muscles That Move the Forearm

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Figure 5. (Click on the image to enlarge)

Muscles That Move the Wrist, Hand, and Fingers

Wrist, hand, and finger movements are facilitated by two groups of muscles. The forearm is the origin of the extrinsic muscles of the hand. The palm is the origin of the intrinsic muscles of the hand.

Muscles of the Arm That Move the Wrists, Hands, and Fingers

The muscles in the anterior compartment of the forearm (anterior flexor compartment of the forearm) originate on the humerus and insert onto different parts of the hand. These make up the bulk of the forearm. From lateral to medial, the superficial anterior compartment of the forearm includes the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor digitorum superficialis. The flexor digitorum superficialis flexes the hand as well as the digits at the knuckles, which allows for rapid finger movements, as in typing or playing a musical instrument (see Figure 6 and Table 2). However, poor ergonomics can irritate the tendons of these muscles as they slide back and forth with the carpal tunnel of the anterior wrist and pinch the median nerve, which also travels through the tunnel, causing Carpal Tunnel Syndrome. The deep anterior compartment produces flexion and bends fingers to make a fist. These are the flexor pollicis longus and the flexor digitorum profundus.

The muscles in the superficial posterior compartment of the forearm (superficial posterior extensor compartment of the forearm) originate on the humerus. These are the extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and the extensor carpi ulnaris.

The muscles of the deep posterior compartment of the forearm (deep posterior extensor compartment of the forearm) originate on the radius and ulna. These include the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis (see Figure 6).

Muscles That Move the Wrist, Hands, and Forearm

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Figure 6. (Click on the image to enlarge)

The tendons of the forearm muscles attach to the wrist and extend into the hand. Fibrous bands called retinacula sheath the tendons at the wrist. The flexor retinaculum extends over the palmar surface of the hand while the extensor retinaculum extends over the dorsal surface of the hand.

Intrinsic Muscles of the Hand

The intrinsic muscles of the hand both originate and insert within it (Figure 7). These muscles allow your fingers to also make precise movements for actions, such as typing or writing. These muscles are divided into three groups. The thenar muscles are on the radial aspect of the palm. The hypothenar muscles are on the medial aspect of the palm, and the intermediate muscles are midpalmar.

The thenar muscles include the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and the adductor pollicis. These muscles form the thenar eminence, the rounded contour of the base of the thumb, and all act on the thumb. The movements of the thumb play an integral role in most precise movements of the hand.

The hypothenar muscles include the abductor digiti minimi, flexor digiti minimi brevis, and the opponens digiti minimi. These muscles form the hypothenar eminence, the rounded contour of the little finger, and as such, they all act on the little finger. Finally, the intermediate muscles act on all the fingers and include the lumbrical, the palmar interossei, and the dorsal interossei.

Intrinsic Muscles of the Hand

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Figure 7: The intrinsic muscles of the hand both originate and insert within the hand. These muscles provide the fine motor control of the fingers by flexing, extending, abducting, and adducting the more distal finger and thumb segments. (Click on the image to enlarge)

Chapter Review

The clavicle and scapula make up the pectoral girdle, which provides a stable origin for the muscles that move the humerus. The muscles that position and stabilize the pectoral girdle are located on the thorax. The anterior thoracic muscles are the subclavius, pectoralis minor, and the serratus anterior. The posterior thoracic muscles are the trapezius, levator scapulae, rhomboid major, and rhomboid minor. Nine muscles cross the shoulder joint to move the humerus. The ones that originate on the axial skeleton are the pectoralis major and the latissimus dorsi. The deltoid, subscapularis, supraspinatus, infraspinatus, teres major, teres minor, and coracobrachialis originate on the scapula.

The forearm flexors include the biceps brachii, brachialis, and brachioradialis. The extensors are the triceps brachii and anconeus. The pronators are the pronator teres and the pronator quadratus. The supinator is the only one that turns the forearm anteriorly.

The extrinsic muscles of the hands originate along the forearm and insert into the hand in order to facilitate crude movements of the wrists, hands, and fingers. The superficial anterior compartment of the forearm produces flexion. These muscles are the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and the flexor digitorum superficialis. The deep anterior compartment produces flexion as well. These are the flexor pollicis longus and the flexor digitorum profundus. The rest of the compartments produce extension. The extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris are the muscles found in the superficial posterior compartment. The deep posterior compartment includes the abductor longus, extensor pollicis brevis, extensor pollicis longus, and the extensor indicis.

Finally, the intrinsic muscles of the hands allow our fingers to make precise movements, such as typing and writing. They both originate and insert within the hand. The thenar muscles, which are located on the lateral part of the palm, are the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and adductor pollicis. The hypothenar muscles, which are located on the medial part of the palm, are the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi. The intermediate muscles, located in the middle of the palm, are the lumbricals, palmar interossei, and dorsal interossei.

Review Questions

Exercise 1

The rhomboid major and minor muscles are deep to the ________.

  1. rectus abdominis
  2. scalene muscles
  3. trapezius
  4. ligamentum nuchae

Show/Hide Solution

C

Exercise 2

Which muscle extends the forearm?

  1. biceps brachii
  2. triceps brachii
  3. brachialis
  4. deltoid

Show/Hide Solution

B

Exercise 3

What is the origin of the wrist flexors?

  1. the lateral epicondyle of the humerus
  2. the medial epicondyle of the humerus
  3. the carpal bones of the wrist
  4. the deltoid tuberosity of the humerus

Show/Hide Solution

B

Exercise 4

Which muscles stabilize the pectoral girdle?

  1. axial and scapular
  2. axial
  3. appendicular
  4. axial and appendicular

Show/Hide Solution

A

Critical Thinking Questions

Exercise 5

The tendons of which muscles form the rotator cuff? Why is the rotator cuff important?

Show/Hide Solution

Tendons of the infraspinatus, supraspinatus, teres minor, and the subscapularis form the rotator cuff, which forms a foundation on which the arms and shoulders can be stabilized and move.

Exercise 6

List the general muscle groups of the shoulders and upper limbs as well as their subgroups.

Show/Hide Solution

The muscles that make up the shoulders and upper limbs include the muscles that position the pelvic girdle, the muscles that move the humerus, the muscles that move the forearm, and the muscles that move the wrists, hands, and fingers.

Glossary

abductor digiti minimi
muscle that abducts the little finger

adductor pollicis
muscle that adducts the thumb

abductor pollicis brevis
muscle that abducts the thumb

abductor pollicis longus
muscle that inserts into the first metacarpal

anconeus
small muscle on the lateral posterior elbow that extends the forearm

anterior compartment of the arm
(anterior flexor compartment of the arm) the biceps brachii, brachialis, brachioradialis, and their associated blood vessels and nerves

anterior compartment of the forearm
(anterior flexor compartment of the forearm) deep and superficial muscles that originate on the humerus and insert into the hand

biceps brachii
two-headed muscle that crosses the shoulder and elbow joints to flex the forearm while assisting in supinating it and flexing the arm at the shoulder

brachialis
muscle deep to the biceps brachii that provides power in flexing the forearm.

brachioradialis
muscle that can flex the forearm quickly or help lift a load slowly

coracobrachialis
muscle that flexes and adducts the arm

deep anterior compartment
flexor pollicis longus, flexor digitorum profundus, and their associated blood vessels and nerves

deep posterior compartment of the forearm
(deep posterior extensor compartment of the forearm) the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, and their associated blood vessels and nerves

deltoid
shoulder muscle that abducts the arm as well as flexes and medially rotates it, and extends and laterally rotates it

dorsal interossei
muscles that abduct and flex the three middle fingers at the metacarpophalangeal joints and extend them at the interphalangeal joints

extensor carpi radialis brevis
muscle that extends and abducts the hand at the wrist

extensor carpi ulnaris
muscle that extends and adducts the hand

extensor digiti minimi
muscle that extends the little finger

extensor digitorum
muscle that extends the hand at the wrist and the phalanges

extensor indicis
muscle that inserts onto the tendon of the extensor digitorum of the index finger

extensor pollicis brevis
muscle that inserts onto the base of the proximal phalanx of the thumb

extensor pollicis longus
muscle that inserts onto the base of the distal phalanx of the thumb

extensor radialis longus
muscle that extends and abducts the hand at the wrist

extensor retinaculum
band of connective tissue that extends over the dorsal surface of the hand

extrinsic muscles of the hand
muscles that move the wrists, hands, and fingers and originate on the arm

flexor carpi radialis
muscle that flexes and abducts the hand at the wrist

flexor carpi ulnaris
muscle that flexes and adducts the hand at the wrist

flexor digiti minimi brevis
muscle that flexes the little finger

flexor digitorum profundus
muscle that flexes the phalanges of the fingers and the hand at the wrist

flexor digitorum superficialis
muscle that flexes the hand and the digits

flexor pollicis brevis
muscle that flexes the thumb

flexor pollicis longus
muscle that flexes the distal phalanx of the thumb

flexor retinaculum
band of connective tissue that extends over the palmar surface of the hand

hypothenar
group of muscles on the medial aspect of the palm

hypothenar eminence
rounded contour of muscle at the base of the little finger

infraspinatus
muscle that laterally rotates the arm

intermediate
group of midpalmar muscles

intrinsic muscles of the hand
muscles that move the wrists, hands, and fingers and originate in the palm

latissimus dorsi
broad, triangular axial muscle located on the inferior part of the back

lumbrical
muscle that flexes each finger at the metacarpophalangeal joints and extend each finger at the interphalangeal joints

opponens digiti minimi
muscle that brings the little finger across the palm to meet the thumb

opponens pollicis
muscle that moves the thumb across the palm to meet another finger

palmar interossei
muscles that abduct and flex each finger at the metacarpophalangeal joints and extend each finger at the interphalangeal joints

palmaris longus
muscle that provides weak flexion of the hand at the wrist

pectoral girdle
shoulder girdle, made up of the clavicle and scapula

pectoralis major
thick, fan-shaped axial muscle that covers much of the superior thorax

pectoralis minor
muscle that moves the scapula and assists in inhalation

pronator quadratus
pronator that originates on the ulna and inserts on the radius

pronator teres
pronator that originates on the humerus and inserts on the radius

retinacula
fibrous bands that sheath the tendons at the wrist

rhomboid major
muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae

rhomboid minor
muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae

rotator cuff
(also, musculotendinous cuff) the circle of tendons around the shoulder joint

serratus anterior
large and flat muscle that originates on the ribs and inserts onto the scapula

subclavius
muscle that stabilizes the clavicle during movement

subscapularis
muscle that originates on the anterior scapula and medially rotates the arm

superficial anterior compartment of the forearm
flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis, and their associated blood vessels and nerves

superficial posterior compartment of the forearm
extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and their associated blood vessels and nerves

supinator
muscle that moves the palm and forearm anteriorly

supraspinatus
muscle that abducts the arm

teres major
muscle that extends the arm and assists in adduction and medial rotation of it

teres minor
muscle that laterally rotates and extends the arm

thenar
group of muscles on the lateral aspect of the palm

thenar eminence
rounded contour of muscle at the base of the thumb

trapezius
muscle that stabilizes the upper part of the back

triceps brachii
three-headed muscle that extends the forearm