Muscles Acting on the Wrist and Hand

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The hand is acted upon by extrinsic muscles in the forearm and intrinsic muscles in the hand itself (table 10.14). The bellies of the extrinsic muscles form the fleshy roundness of the proximal forearm; their tendons extend into the wrist and hand. Their actions are mainly flexion and extension, but the wrist and fingers can be abducted and adducted, and the thumb and fingers can be opposed.

46ancon = elbow

Flexion Biceps brachii Brachialis

Brachioradialis Flexor carpi radialis (Pronator teres)

Pronation Pronator teres

Pronator quadratus

Extension Triceps brachii

Anconeus

Supination Supinator

Biceps brachii

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362 Part Two Support and Movement

Table 10.13 Muscles Acting on the Forearm (see figs. 10.22 and 10.25)

O = origin, I = insertion, N = innervation (n. = nerve, nn. = nerves)

Table 10.13 Muscles Acting on the Forearm (see figs. 10.22 and 10.25)

O = origin, I = insertion, N = innervation (n. = nerve, nn. = nerves)

Muscles with Bellies in the Arm (Brachium)

Biceps Brachii (BY-seps BRAY-kee-eye)

Flexes elbow; abducts arm; supinates forearm; holds head of humerus in glenoid cavity

O: long head—supraglenoid tubercle of scapula; short head—coracoid process of scapula

I: radial tuberosity

N: musculocutaneous n.

Brachialis (BRAY-kee-AL-iss)

Flexes elbow

O: anterior distal shaft of humerus

I: coronoid process of ulna, capsule of elbow joint

N: musculocutaneous n., radial n.

Triceps Brachii (TRI-seps BRAY-kee-eye)

Extends elbow; long head adducts humerus

O: long head—infraglenoid tubercle of scapula; lateral head—proximal posterior shaft of humerus; medial head—posterior shaft of humerus

I: olecranon of ulna

N: radial n.

Muscles with Bellies in the Forearm (Antebrachium)

Brachioradialis (BRAY-kee-oh-RAY-dee-AL-iss)

Flexes elbow

O: lateral supracondylar ridge of humerus

I: styloid process of radius

N: radial n.

Anconeus (an-CO-nee-us)

Extends elbow

O: lateral epicondyle of humerus

I: olecranon and posterior aspect of ulna

N: radial n.

Pronator Teres (PRO-nay-tur TERR-eez)

Pronates forearm

O: medial epicondyle of humerus, coronoid process of ulna

I: lateral midshaft of radius

N: median n.

Pronator Quadratus (PRO-nay-tur quad-RAY-tus)

Pronates forearm

O: anterior distal shaft of ulna

I: anterior distal shaft of radius

N: median n.

Supinator (SOO-pih-NAY-tur)

Supinates forearm

O: lateral epicondyle of humerus, proximal shaft of ulna

I: proximal shaft of radius

N: radial n.

Saladin: Anatomy & I 10. The Muscular System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 10 The Muscular System 363

Supination

71 f

Pronation epicondyle Supinator

Radius

Medial epicondyle

Pronator teres

Supination

Pronation

Medial epicondyle

Pronator teres epicondyle Supinator

Radius

Pronator Teres Pronation

(c) Supinator

Figure 10.25 Actions of the Rotator Muscles on the Forearm. (a) Supination; (b) pronation; (c) cross section just distal to the elbow, showing how the biceps brachii aids in supination.

What do the names of the pronator teres and pronator quadratus muscles indicate about their shapes?

(c) Supinator

Figure 10.25 Actions of the Rotator Muscles on the Forearm. (a) Supination; (b) pronation; (c) cross section just distal to the elbow, showing how the biceps brachii aids in supination.

What do the names of the pronator teres and pronator quadratus muscles indicate about their shapes?

Table 10.14 Muscles Acting on the Wrist and Hand (see figs. 10.27 and 10.28)

O = origin, I = insertion, N = innervation (n. = nerve, nn. = nerves)

Anterior Compartment—Superficial Layer

Flexor Carpi Radialis (CAR-pie RAY-dee-AY-liss)

Powerful wrist flexor; abducts hand; synergist in elbow flexion O: medial epicondyle of humerus

Flexor Carpi Ulnaris (ul-NAY-riss)

Flexes and adducts wrist; stabilizes wrist during extension of fingers O: medial epicondyle of humerus

I: base of metacarpals II and III

I: pisiform, hamate, metacarpal V

Flexor Digitorum Superficialis (DIDJ-ih-TOE-rum SOO-per-FISH-ee-AY-liss)

Flexes fingers II—V at proximal interphalangeal joints; aids in flexion of wrist and metacarpophalangeal joints

O: medial epicondyle of humerus, radius, coronoid process of ulna I: four tendons leading to middle phalanges II—V

Palmaris (pall-MERR-iss) Longus

Weakly flexes wrist; often absent O: medial epicondyle of humerus

I: palmar aponeurosis, flexor retinaculum

N: median n.

1 Saladin: Anatomy & 1 10. The Muscular System 1 Text 1 Physiology: The Unity of Form and Function, Third Edition

© The McGraw-Hill Companies, 2003

364 Part Two Support and Movement

Table 10.14 Muscles Acting on the Wrist and Hand (see figs. 10.27 and 10.28) (continued)

Anterior Compartment—Deep Layer

Flexor Digitorum Profundus

Flexes wrist and distal interphalangeal joints

O: shaft of ulna, interosseous membrane I: four tendons to distal phalanges II—V

N: median and ulnar nn.

Flexor Pollicis (PAHL-ih-sis) Longus

Flexes interphalangeal joint of thumb; weakly flexes wrist

O: radius, interosseous membrane I: distal phalanx I

N: median n.

Posterior Compartment—Superficial Layer

Extensor Carpi Radialis Longus

Extends and abducts wrist

O: lateral epicondyle of humerus I: base of metacarpal II

N: radial n.

Extensor Carpi Radialis Brevis

Extends and abducts wrist; fixes wrist during finger flexion

O: lateral epicondyle of humerus I: base of metacarpal III

N: radial n.

Extensor Carpi Ulnaris

Extends and adducts wrist

O: lateral epicondyle of humerus, posterior shaft of ulna I: base of metacarpal V

N: radial n.

Extensor Digitorum (DIDJ-ih-TOE-rum)

Extends fingers II—V at metacarpophalangeal joints

O: lateral epicondyle of humerus I: dorsal aspect of phalanges II-V

N: radial n.

Extensor Digiti Minimi (DIDJ-ih-ty MIN-in-my)

Extends metacarpophalangeal joint of little finger; sometimes considered to be a detached portion of extensor digitorum O: lateral epicondyle of humerus I: distal and middle phalanges V

N: radial n.

Posterior Compartment—Deep Layer

Abductor Pollicis Longus

Abducts and extends thumb; abducts wrist

O: posterior aspect of radius and ulna, interosseous membrane I: trapezium, base of metacarpal I

N: radial n.

Extensor Indicis (IN-dih-sis)

Extends index finger at metacarpophalangeal joint

O: shaft of ulna, interosseous membrane I: middle and distal phalanges II

N: radial n.

Extensor Pollicis Longus

Extends thumb at metacarpophalangeal joint

O: shaft of ulna, interosseous membrane I: distal phalanx I

N: radial n.

Extensor Pollicis Brevis

Extends thumb at metacarpophalangeal joint

O: shaft of radius, interosseous membrane I: proximal phalanx I

N: radial n.

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

Trapezium

Palmar Carpal Ligament

Superficial palmar arterial arch

Palmaris longus tendon

Flexor carpi radialis tendon

Flexor pollicis longus tendon Palmar carpal ligament (cut) Median nerve Radial artery

Trapezium

Chapter 10 The Muscular System 365

Flexor digitorum superficialis tendon

Flexor digitorum profundus tendon

Flexor carpi ulnaris tendon Ulnar artery

Ulnar nerve

Flexor retinaculum covering carpal tunnel

Bursa

Superficial palmar arterial arch

Thenar muscles Median nerve

Flexor carpi radialis tendon

Carpal tunnel

Flexor digitorum profundus tendons

Trapezium Radial artery Trapezoid Scaphoid

Thenar muscles Median nerve

Flexor carpi radialis tendon

Carpal tunnel

Cross Sectional Anatomy Thenar Muscles

Dorsal

Figure 10.26 The Carpal Tunnel. (a) Dissection of the wrist (anterior aspect) showing the tendons, nerve, and bursae that pass under the flexor retinaculum. (b) Cross section of the wrist, ventral (anterior side) up. Note how the flexor tendons and median nerve are confined in the tight space between the carpal bones and flexor retinaculum.

Ulnar artery Ulnar nerve Flexor retinaculum covering carpal tunnel

Ulnar bursa Hypothenar muscles

Flexor digitorum superficialis tendons

Hamate Capitate

Extensor tendons

Dorsal

Figure 10.26 The Carpal Tunnel. (a) Dissection of the wrist (anterior aspect) showing the tendons, nerve, and bursae that pass under the flexor retinaculum. (b) Cross section of the wrist, ventral (anterior side) up. Note how the flexor tendons and median nerve are confined in the tight space between the carpal bones and flexor retinaculum.

It may seem as if the tendons would stand up like taut bowstrings when these muscles contracted, but this is prevented by the fact that most of them pass under a flexor retinaculum (transverse carpal ligament) on the anterior side of the wrist and an extensor retinaculum (dorsal carpal ligament) on the posterior side (see fig. 10.29). The carpal tunnel is a tight space between the carpal bones and flexor retinaculum (fig. 10.26). The flexor tendons passing through the tunnel are enclosed in tendon sheaths that enable them to slide back and forth quite easily, although this region is very subject to injury from repetitive motion (see insight 10.4).

Insight 10.4 Clinical Application

Carpal Tunnel Syndrome

Prolonged, repetitive motions of the wrist and fingers can cause tissues in the carpal tunnel to become inflamed, swollen, or fibrotic. Since the carpal tunnel cannot expand, swelling puts pressure on the median nerve of the wrist, which passes through the carpal tunnel with the flexor tendons. This pressure causes tingling and muscular weakness in the palm and medial side of the hand and pain that may radiate to the arm and shoulder. This condition, called carpal tunnel syndrome, is common among keyboard operators, pianists, meat cutters, and others

Saladin: Anatomy & I 10. The Muscular System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

366 Part Two Support and Movement who spend long hours making repetitive wrist motions. Carpal tunnel syndrome is treated with aspirin and other anti-inflammatory drugs, immobilization of the wrist, and sometimes surgical removal of part or all of the flexor retinaculum to relieve pressure on the nerve.

Several of these muscles originate on the humerus; therefore, they cross the elbow joint and weakly contribute to flexion and extension of the elbow. This action is relatively negligible, however, and we focus on their action at the wrist and fingers. Although these muscles are numerous and complex, most of their names suggest their actions, and from their actions, their approximate locations in the forearm can generally be deduced.

The deep fasciae divide the muscles of the forearm into anterior and posterior compartments and each compartment into superficial and deep layers (fig. 10.27). The muscles are listed and classified this way in table 10.14. Most muscles of the anterior compartment are flexors of the wrist and fingers that arise from a common tendon on the humerus (fig. 10.28). At the distal end, the tendon of the palmaris longus passes over the flexor retinaculum while the other tendons pass beneath it. The two prominent tendons that you can palpate at the wrist belong to the palmaris longus on the medial side and the flexor carpi radialis on the lateral side. The latter is an important landmark for finding the radial artery, where the pulse is usually taken.

Muscles of the posterior compartment are mostly wrist and finger extensors that share a single proximal tendon arising from the humerus. One of the superficial muscles on this side, the extensor digitorum, has four distal tendons that can easily be seen and palpated on the back of the hand when the fingers are strongly hyperex-tended (fig. 10.28d, and see fig. B.8 in the atlas following this chapter). By strongly abducting and extending the thumb into a hitchhiker's position, you should also be able to see a deep dorsolateral pit at the base of the thumb, with a taut tendon on each side of it. This depression is called the anatomical snuffbox because it was once fashionable to place a pinch of snuff here and inhale it (see fig. B.8). It is bordered laterally by the tendons of the abductor polli-cis longus and extensor pollicis brevis and medially by the tendon of the extensor pollicis longus.

Other muscles of the forearm were considered earlier because they act on the radius and ulna rather than on the hand. These are the pronator quadratus, pronator teres, supinator, anconeus, and brachioradialis.

Table 10.15 summarizes the muscles responsible for the major movements of the wrist and hand.

Think About It

Why are the prime movers of finger extension and flexion located in the forearm rather than in the hand, closer to the fingers?

The intrinsic muscles of the hand assist the flexors and extensors of the forearm and make finger movements more precise (fig. 10.29). You will note in table 10.16 that they are divided into three groups. The thenar group forms the thick fleshy mass (thenar eminence) at the base of the thumb, except for the adductor pollicis, which forms the web between the thumb and palm; the hypothenar group forms the fleshy mass (hypothenar eminence) at the base of the little finger; and the midpal-mar group occupies the space between these. The mid-palmar group consists of 11 muscles divided into three subgroups:

1. Dorsal interosseous47 muscles—four bipennate muscles attached to both sides of the metacarpal bones, serving to abduct (spread) the fingers.

2. Palmar interosseous muscles—three unipennate muscles that arise from metacarpals II, IV, and V and adduct the fingers (draw them together).

3. Lumbrical48 muscles—four wormlike muscles that flex the metacarpophalangeal joints (proximal knuckles) but extend the interphalangeal joints (distal knuckles).

Before You Go On

Answer the following questions to test your understanding of the preceding section:

17. Name a muscle that inserts on the scapula and plays a significant role in each of the following actions: (a) pushing a stalled car, (b) paddling a canoe, (c) squaring the shoulders in military attention, (d) lifting the shoulder to carry a heavy box on it, and (e) lowering the shoulder to lift a suitcase.

18. Describe three contrasting actions of the deltoid muscle.

19. Name the four rotator cuff muscles and identify the scapular surfaces against which they lie.

20. Name the prime movers of elbow flexion and extension.

21. Identify three functions of the biceps brachii.

22. Name three extrinsic muscles and two intrinsic muscles that flex the phalanges.

48 lumbric = earthworm

Insight 10.5 Clinical Application

Intramuscular Injections

Muscles with thick bellies are commonly used for intramuscular (I.M.) drug injections. Since drugs injected into these muscles are absorbed into the bloodstream gradually, it is safe to administer relatively large doses (up to 5 mL) that could be dangerous or even fatal if injected directly into the bloodstream. I.M. injections also cause less tissue irritation than subcutaneous injections.

Knowledge of subsurface anatomy is necessary to avoid damaging nerves or accidentally injecting a drug into a blood vessel. Anatomical

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

Chapter 10 The Muscular System 367

Superficial flexors Deep flexors Superficial extensors Other muscles

Subcutaneous Injections Triceps Long Head Triceps Brachii Cross Section

Biceps brachii

Brachialis

Triceps brachii Medial head Long head Lateral head

Deltoid

Pectoralis major

Biceps brachii Short head Long head

Coracobrachialis Humerus

Latissimus dorsi tendon Teres major

Triceps brachii Lateral head Long head

Biceps brachii

Brachialis

Triceps brachii Medial head Long head Lateral head

Brachioradialis Supinator Radius

Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris (c)

Extensor Carpi Radialis Longus Muscle

Figure 10.27 Serial Cross Sections Through the Upper Limb. Each section is taken at the correspondingly lettered level in the figure at the left and is pictured with the posterior muscle compartment facing the bottom of the page, as if you were viewing the right arm of a person facing you with the arm extended and the palm up.

Why are the extensor pollicis longus and extensor indicis not seen in figure c?

Pronator teres Flexor carpi radialis Palmaris longus Flexor digitorum superficialis

Flexor pollicis longus Flexor carpi ulnaris Flexor digitorum profundus Ulna

Anconeus

Figure 10.27 Serial Cross Sections Through the Upper Limb. Each section is taken at the correspondingly lettered level in the figure at the left and is pictured with the posterior muscle compartment facing the bottom of the page, as if you were viewing the right arm of a person facing you with the arm extended and the palm up.

Why are the extensor pollicis longus and extensor indicis not seen in figure c?

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

Brachialis

Biceps brachii

Brachialis

Pronator teres

Brachioradialis

Flexor carpi radialis

Palmaris longus

Flexor carpi ulnaris

Flexor pollicis longus

Pronator quadratus

Flexor Digitorum Profundus Cross Section

Flexor Flexor digitorum superficialis

Supinator

Flexor digitorum profundus

Flexor pollicis longus

Supinator Longus

Supinator

Pronator quadratus

Pronator quadratus

Anconeus And Biceps Brachii
Triceps brachii

Anconeus

Flexor carpi ulnaris

Extensor carpi ulnaris

Extensor digiti minimi

Tendons of extensor digitorum

Anconeus

Flexor carpi ulnaris

Extensor carpi ulnaris

Extensor digiti minimi

Tendons of extensor digitorum

Extensor Polli Longus Tendon

Brachioradialis

Extensor carpi radialis longus

Extensor carpi radialis brevis

Extensor digitorum

Abductor pollicis longus

Extensor pollicis brevis

Extensor pollicis longus

Tendons of extensor carpi radialis longus and brevis

Olecranon

Extensor pollicis longus

Extensor indicis

Anconeus Supinator

Olecranon

Extensor pollicis longus

Extensor indicis

Abductor Pollicis Longus

Abductor pollicis longus

Extensor pollicis

Anconeus Supinator

Abductor pollicis longus

Extensor pollicis

Figure 10.28 Muscles of the Forearm. Figures a-c are anterior views and figures d-e are posterior. Boldface labels indicate: (a) superficial flexors; (b) the flexor digitorum superficialis, deep to the muscles in a but also classified as a superficial flexor; (c) deep flexors; (d) superficial extensors; and (e) deep extensors.

Saladin: Anatomy & I 10. The Muscular System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Table 10.15 Actions of the Wrist and Hand

Chapter 10 The Muscular System 369

Boldface indicates prime movers; others are synergists. Parentheses indicate only a slight effect.

Table 10.15 Actions of the Wrist and Hand

Boldface indicates prime movers; others are synergists. Parentheses indicate only a slight effect.

Wrist Flexion

Wrist Extension

Flexor carpi radialis

Extensor digitorum

Flexor carpi ulnaris

Extensor carpi radialis longus

Flexor digitorum superficialis

Extensor carpi radialis brevis

(Palmaris longus)

Extensor carpi ulnaris

(Flexor pollicis longus)

Wrist Abduction

Wrist Adduction

Flexor carpi radialis

Flexor carpi ulnaris

Extensor carpi radialis longus

Extensor carpi ulnaris

Extensor carpi radialis brevis

Abductor pollicis longus

Finger Flexion

Finger Extension Thumb Opposition

Flexor digitorum

Extensor pollicis

Opponens pollicis

superficialis

longus

Opponens digiti minimi

Flexor digitorum

Extensor pollicis

profundus

brevis

Flexor pollicis longus

Extensor digitorum

Extensor indicis

knowledge also enables a clinician to position a patient so that the muscle is relaxed, making the injection less painful.

Amounts up to 2 mL are commonly injected into the deltoid muscle about two finger widths below the acromion. Amounts over 2 mL are commonly injected into the gluteus medius, in the superolateral quadrant of the gluteal area, at a safe distance from the sciatic nerve and major gluteal blood vessels. Injections are often given to infants and young children in the vastus lateralis of the thigh, because their deltoid and gluteal muscles are not well developed.

The largest and strongest muscles in the body are found in the lower limb. Unlike those of the upper limb, they are adapted less for precision than for the strength needed to stand, maintain balance, walk, and run. Several of them cross and act upon two or more joints, such as the hip and knee.

To avoid confusion in this discussion, remember that in the anatomical sense the word leg refers only to that part of the limb between the knee and ankle. The term foot includes the tarsal region (ankle), metatarsal region, and toes.

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  • fre-swera
    What are the synergists for finger flexion?
    6 years ago

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