- 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.
|Table 1. Muscles that Position the Pectoral Girdle|
|Position in the Thorax||Movement||Target||Target motion direction||Prime mover||Origin||Insertion|
|Anterior thorax||Stabilizes clavicle during movement by depressing it||Clavicle||Depression||Subclavius||First rib||Inferior surface of clavicle|
|Anterior thorax||Rotates shoulder anteriorly (throwing motion); assists with inhalation||Scapula; ribs||Scapula: depresses; ribs: elevates||Pectoralis minor||Anterior surfaces of certain ribs (2–4 or 3–5)||Coracoid process of scapula|
|Anterior thorax||Moves arm from side of body to front of body; assists with inhalation||Scapula; ribs||Scapula: protracts; ribs: elevates||Serratus anterior||Muscle slips from certain ribs (1–8 or 1–9)||Anterior surface of vertebral border of scapula|
|Posterior thorax||Elevates shoulders (shrugging); pulls shoulder blades together; tilts head backwards||Scapula; cervical spine||Scapula: rotates inferiorly, retracts, elevates, and depresses; spine: extends||Trapezius||Skull; vertebral column||Acromion and spine of scapula; clavicle|
|Posterior thorax||Stabilizes scapula during pectoral girdle movement||Scapula||Retracts; rotates inferiorly||Rhomboid major||Thoracic vertebrae (T2–T5)||Medial border of scapula|
|Posterior thorax||Stabilizes scapula during pectoral girdle movement||Scapula||Retracts; rotates inferiorly||Rhomboid minor||Cervical and thoracic vertebrae (C7 and T1)||Medial border of scapula|
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, Figure 3, and Table 2).
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.
|Table 2. Muscles That Move the Humerus|
|Movement||Target||Target motion direction||Prime mover||Origin||Insertion|
|Brings elbows together; moves elbow up (as during an uppercut punch)||Humerus||Flexion; adduction; medial rotation||Pectoralis major||Clavicle; sternum; cartilage of ribs (1–6 or 1–7); aponeurosis of external oblique muscle||Greater tubercle of humerus|
|Moves elbow back (as in elbowing someone standing behind you); spreads elbows apart||Humerus; scapula||Humerus: extension, adduction, and medial rotation; scapula: depression||Latissimus dorsi||Thoracic vertebrae (T7–T12); lumbar vertebrae; lower ribs (9–12); iliac crest||Intertubercular sulcus of humerus|
|Lifts arms at the shoulder||Humerus||Abduction; flexion; extension; medial and lateral rotation||Deltoid||Trapezius; clavicle; acromion; spine of scapula||Nasal bone|
|Assists the pectoralis major in bringing the elbows together and stabilizes the shoulder joint during movement of the pectoral girdle||Humerus||Medial rotation||Subscapularis||Subscapular fossa of the scapula||Lesser tubercle of humerus|
|Rotates the elbow outwards, as during a tennis swing||Humerus||Abduction||Supraspinatus||Supraspinous fossa of the scapula||Greater tubercle of humerus|
|Rotates the elbow outwards, as during a tennis swing||Humerus||Extension; adduction||Infraspinatus||Infraspinous fossa of the scapula||Greater tubercle of humerus|
|Assists the infraspinatus in rotating the elbow outwards||Humerus||Extension; adduction||Teres major||Posterior surface of the scapula||Intertubercular sulcus of humerus|
|Assists the infraspinatus in rotating the elbow outwards||Humerus||Extension; adduction||Teres minor||Lateral border of the dorsal scapular surface||Greater tubercle of humerus|
|Moves the elbow up and across the body, as when putting a hand on the chest||Humerus||Flexion; adduction||Coracobra chialis||Coracoid process of the scapula||Medial surface of humerus shaft|
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 Table 3).
|Table 3. Muscles That Move the Forearm|
|Movement||Target||Target motion direction||Prime mover||Origin||Insertion|
|Anterior muscles (flexion)|
|Performs a bicep curl; also allows palm of hand to point toward body while flexing||Forearm||Flexion; supination||Biceps brachii||Coracoid process; tubercle above glenoid cavity||Radial tuberosity|
|Forearm||Flexion||Brachialis||Front of distal humerus||Coronoid process of ulna|
|Assists and stabilizes elbow during bicep-curl motion||Forearm||Flexion||Brachioradialis||Lateral supracondylar ridge at distal end of humerus||Base of styloid process of radius|
|Posterior muscles (extension)|
|Extends forearm, as during a punch||Forearm||Extension||Triceps brachii||Infraglenoid tubercle of scapula; posterior shaft of humerus; posterior humeral shaft distal to radial groove||Olecranon process of ulna|
|Assists in extending forearm; also allows forearm to extend away from body||Forearm||Extension; abduction||Anconeus||Lateral epicondyle of humerus||Lateral aspect of olecranon process of ulna|
|Anterior muscles (pronation)|
|Turns hand palm-down||Forearm||Pronation||Pronator teres||Medial epicondyle of humerus; coronoid process of ulna||Lateral radius|
|Assists in turning hand palm-down||Forearm||Pronation||Pronator quadratus||Distal portion of anterior ulnar shaft||Distal surface of anterior radius|
|Posterior muscles (supination)|
|Tuns hand palm-up||Forearm||Supination||Supinator||Lateral epicondyle of humerus; proximal ulna||Proximal end of radius|
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 Table 4). 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 Table 4).
|Table 4. Muscles That Move the Wrist, Hands, and Forearm|
|Movement||Target||Target motion direction||Prime mover||Origin||Insertion|
|Superficial anterior compartment of forearm|
|Bends the wrist toward the body; it also tilts the hand to the side away from the body||Wrist; hand||Flexion; abduction||Flexor carpi radialis||Medial epicondyle of the humerus||Base of second and third metacarpals|
|Assists in bending the hand up toward the shoulder||Wrist||Flexion||Palmaris longus||Medial epicondyle of the humerus||Palmar aponeurosis; skin and fascia of palm|
|Assists in bending the hand up toward the shoulder; it also tilts the hand to the side away from the body and stabilizes the wrist||Wrist; hand||Flexion; abduction||Flexor carpi ulnaris||Medial epicondyle of the humerus, the olecranon process, and the posterior surface of the ulna||Pisiform, hamate bones, and base of fifth metacarpal|
|Bends the fingers to make a fist||Wrist; fingers 2–5||Flexion||Flexor digitorum superficialis||Medial epicondyle of the humerus, the coronoid process of the ulna, and the shaft of the radius||Middle phalanges of fingers 2–5|
|Deep anterior compartment of forearm|
|Bends the tip of the thumb||Thumb||Flexion||Flexor pollicis longus||Anterior surface of the radius and the interosseous membrane||Distal phalanx of thumb|
|Bends the fingers to make a fist; it also bends the wrist toward the body||Wrist; fingers||Flexion||Flexor digitorum profundus||Coronoid process, the anteromedial surface of the ulna, and the interosseous membrane||Distal phalanges of fingers 2–5|
|Superficial posterior compartment of forearm|
|Straightens the wrist away from the body; it also tilts the hand to the side away from the body||Wrist||Extension; abduction||Extensor radialis longus||Lateral supracondylar ridge of the humerus||Base of second metacarpal|
|Assists the extensor radialis longus in extending and abducting the wrist; it also stabilizes the hand during finger flexion||Wrist||Extension; abduction||Extensor carpi radialis brevis||Lateral epicondyle of the humerus||Base of third metacarpal|
|Opens the fingers and moves them sideways away from the body||Wrist; fingers||Extension; abduction||Extensor digitorum||Lateral epicondyle of the humerus||Extensor expansions; distal phalanges of fingers|
|Extends the little finger||Little finger||Extension||Extensor digiti minimi||Lateral epicondyle of the humerus||Extensor expansion; distal phalanx of finger 5|
|Straightens the wrist away from the body; it also tilts the hand to the side toward the body||Wrist||Extension; abduction||Extensor carpi ulnaris||Lateral epicondyle of the humerus and the posterior of the ulna||Base of fifth metacarpal|
|Deep posterior compartment of forearm|
|Moves the thumb sideways toward the body; it also extends the thumb and moves the hand sideways toward the body||Wrist; thumb||Thumb: abduction, extension; wrist: abduction||Abductor pollicis longus||Posterior surface of the radius and ulna and in the interosseous membrane||Base of first metacarpal; trapezium|
|Extends the thumb||Thumb||Extension||Extensor pollicis brevis||Dorsal shaft of the radius and ulna and in the interosseous membrane||Base of proximal phalanx of thumb|
|Extends the thumb||Thumb||Extension||Extensor pollicis longus||Dorsal shaft of the radius and ulna and in the interosseous membrane||Base of distal phalanx of thumb|
|Extends the index finger; it also straightens the wrist away from the body||Wrist; index finger||Extension||Extensor indicis||Posterior surface of the distal ulna and in the interosseous membrane||Tendon of extensor digitorum of finger|
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 5). 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.
|Table 5. Muscles That Move the Wrist, Hands, and Forearm|
|Muscle||Movement||Target||Target motion direction||Prime mover||Origin||Insertion|
|Thenar muscles||Moves thumb toward body||Thumb||Abduction||Abductor pollicis brevis||Flexor retinaculum; nearby carpals||Lateral base of proximal phalanx of thumb|
|Thenar muscles||Moves thumb across palm toward body||Thumb||Opposition||Opponens pollicis||Flexor retinaculum; trapezium||Anterior of first metacarpal|
|Thenar muscles||Flexes thumb||Thumb||Flexion||Flexor pollicis brevis||Felxor retinaculum; trapezium||Lateral base of proximal phalanx of thumb|
|Thenar muscles||Moves thumb away from body||Thumb||Adduction||Adductor pollicis||Capitate bone; bases of metacarpals 2–4; front of metacarpal||Medial base of proximal phalanx of thumb|
|Hypothenar muscles||Moves little finger toward body||Little finger||Abduction||Abductor digiti minimi||Pisiform bone||Medial side of proximal phalanx of little finger|
|Hypothenar muscles||Flexes little finger||Little finger||Flexion||Flexor digiti minimi brevis||Hamate bone; flexor retinaculum||Medial side of proximal phalanx of little finger|
|Hypothenar muscles||Moves little finger across palm to touch thumb||Little finger||Opposition||Opponens digiti minimi||Hamate bone; flexor retinaculum||Medial side of proximal phalanx of little finger|
|Intermediate muscles||Flexes each finger at metacarpo-phalangeal joints; extends each finger at interphalangeal joints||Fingers||Flexion||Lumbricals||Palm (lateral sides of tendons in flexor digitorum profundus)||Fingers 2–5 (lateral edges of extensional expansions on first phalanges)|
|Intermediate muscles||Adducts and flexes each finger at meacarpo-phalangeal joints; extends each finger at interphalangeal joints||Fingers||Adduction; flexion; extension||Palmar interossei||Side of each metacarpal that faces metacarpal 3 (absent from metacarpal 3)||Extensor expansion on first phalanx of each finger (except finger 3) on side facing finger 3|
|Intermediate muscles||Abducts and flexes the three middle fingers at metacarpo-phalangeal joints; extends the three middle fingers at interphalangeal joints||Fingers||Abduction; flexion; extension||Dorsal interossei||Sides of metacarpals||Both sides of finger 3; for each other finger, extensor expansion over first phalanx on side opposite finger 3|