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Upper Limb muscles and movements

The upper limb (upper extremity) is truly a complex part of human anatomy. It is best studied broken down into its components: regions, joints, muscles, nerves, and blood vessels.

By looking at all of the upper limbs components separately we can appreciate and compartmentalize the information, then later view the upper limb as a whole and understand how all of its parts work in unison.

For this reason, the anatomy of the upper limb from the aspect of muscles will be reviewed topographically. In that manner of speaking, this article will explain all the anatomical aspects of the muscles of the scapula, arm, forearm and hand.

Key Facts
Scapula Teres major, teres minor, infraspinatus, supraspinatus, serratus anterior, subscapularis, levator scapulae, rhomboid major, rhomboid minor, trapezius
Shoulder Pectoralis major, pectoralis minor, deltoid, coracobrachialis, latissimus dorsi
Arm Brachialis, biceps brachii, triceps brachii
Forearm flexors Pronator quadratus, flexor pollicis longus, flexor digitorum profundus, flexor digitorum superficialis, flexor carpi radialis and ulnaris, palmaris longus, pronator teres
Forearm extensors Supinator, extensor digitorum, extensor carpi ulnaris, extensor carpi radialis longus and brevis, extensor indicis proprius, extensor digiti minimi, brachioradialis
Hand Thenar eminence, hypothenar eminence, interossei, lumbricals

In this article we will discuss the gross (structure) and functional anatomy (movement) of the muscles of the upper limb. The hand (manual region) is the terminal end and focus of the upper limb. Human hands are quite special in their anatomy, which allows us to be so dextrous and relies on muscles of the upper limb to help move it through space. We will also discuss the clinical relevance of the upper limb.

Scapular Region

The scapular region lies on the posterior surface of the thoracic wall. It may seem strange that it is included in the anatomy of the upper limb. However, the scapula is integral to the movement of the shoulder via the rotator cuff and additional muscles. The acronym for the rotator cuff is S.I.T.S. which stands for supraspinatus, infraspinatus, teres minor, and subscapularis. The scapula has no direct bony attachments to the thorax, so it is held in place and stabilized through muscular attachment. It is important to note that the scapula does articulate with the acromial end of the clavicle forming the acromioclavicular joint (AC joint), as well as the humeral head with the scapular glenoid cavity (fossa) which forms the glenohumeral joint.

Teres major

Teres major: This muscle arises from the posterior surface of the inferior scapular angle and inserts onto the medial lip of the intertubercular sulcus of the humerus. It acts as an adductor (to ‘add’ to the body), assists in extension and medial rotation, as well as stabilization of the scapula. The lower subscapular nerve innervates the muscle and it is a branch of the posterior cord of the brachial plexus.

Key facts about the teres major
Origins Inferior angle and lower part of the lateral border of the scapula
Insertions Intertubercular sulcus (medial lip) of the humerus
Innervation Lower subscapular nerve
Function Adduction and medial rotation of the humerus (arm)

Teres minor

Teres minor: This muscle arises from the lateral border of the scapula and inserts onto the greater tubercle of the humerus. It acts as a lateral rotator and a weak adductor of the shoulder. It also has a role in stabilizing the humerus and part of the rotator cuff of four muscles.

Key facts about the teres minor muscle
Origins Lateral border of the scapula (middle part)
Insertions Greater tubercle of the humerus (inferior facet)
Innervation Axillary nerve
Function Lateral rotation of the arm, stabilization of the humerus as part of the rotator cuff muscles

This muscle also prevents the humeral head from moving too far upwards while the deltoid is in action, as do all the rotator cuff muscles. The nerve supply to this muscle arises from the axillary nerve, a branch of the posterior cord of the brachial plexus.

Infraspinatus

I nfraspinatus muscle : This muscle is located in the large posterior infraspinous fossa located inferior to the scapular spine. It is the primary lateral rotator of the shoulder, it also modulates deltoid movement. The nerve supply arises from the suprascapular nerve (upper and lower), which arises from the unification of the ventral rami of C5 and C6 spinal nerves (C = cervical).

Key facts about the infraspinatus muscle
Origins Infraspinous fossa of the scapula
Insertions Greater tubercle of the humerus (middle facet)
Innervation Suprascapular nerve
Function Lateral rotation of the arm, stabilization of the humerus as part of the rotator cuff muscles

Supraspinatus

Supraspinatus muscle: This rotator cuff muscle is deep and originates from the supraspinous fossa which is located on the posterior superior portion of the scapula. It acts as an abductor of the shoulder, and inserts onto the superior facet of the greater tubercle of the humerus. It has an essential role in initiating the first 15 degrees of abduction (move away from the body).

Due to this abducting movement, the supraspinatus is commonly referred to as the ‘suitcase’ muscle; i.e.: imagine holding a suitcase or briefcase at your side. This muscle also modulates the movement of the deltoid like the other rotator cuff muscles. However, it prevents the humeral head from slipping downwards. Its innervation is from the upper suprascapular nerve.

Key facts about the supraspinatus muscle
Origins Supraspinous fossa of the scapula
Insertions Greater tubercle of the humerus (superior facet)
Innervation Suprascapular nerve
Function Assistance in arm abduction, stabilization of the humerus as part of the rotator cuff muscles

Serratus anterior

Serratus anterior muscle: This muscle is so named due to its anterior digitations that have a serrated or finger-like appearance. The muscle arises from costals (ribs) 1 - 8, sometimes terminating origins at costal 9. The muscle inserts on the medial part of the anterior border of the scapula.

It passes anteriorly and around the thoracic cage as if wrapping. It functions as a stabilizer of the scapula, acts as a protractor when reaching forward or pushing, and aids in rotation of scapula. This is the reason the muscle is well developed in boxers who protract their scapula in the terminal phases of their punches in order to maximize reach. The nerve supply is from the long thoracic nerve, which arises from the C5, C6, and C7 nerve roots.

Winged scapula is caused by an injury to the long thoracic nerve. It can be observed when a patient circumducts (circle movement) the affected upper limb. The damaged nerve causes a weakened serratus anterior, leading to the scapula not being pulled ‘down’ and ‘in’ during circumduction. This results in a restricted range of motion.

Key facts about the serratus anterior muscle
Origins Lateral parts of the 1st to 8th ribs
Insertions Medial border of the scapula
Innervation Long thoracic nerve
Function Protraction and rotation of the scapula, 

Subscapularis

Subscapularis muscle: This is another muscle of the rotator cuff, which is deep and arises from the large anterior subscapular fossa. It passes laterally to insert onto the lesser tubercle of the humerus. It is the chief medial rotator of the shoulder and modulates the movement of the deltoid. The nerve supply comes from the upper and lower subscapular.

Key facts about the subscapularis muscle
Origins Subscapular fossa
Insertions Lesser tubercle of the humerus
Innervation Upper and lower subscapular nerves
Function Medial rotation of the arm, stabilization of the humerus as part of the rotator cuff muscles

Levator scapulae

Levator scapulae muscle: This is a deep small muscle that inserts onto the superior angle and superior medial scapular border. It arises from the transverse processes of the superior four cervical vertebrae (C1-C4). Its action is elevation of the scapula as well as superior rotation of the scapula. It is innervated by spinal nerves C3-C4 and C5 via the posterior (dorsal) scapular nerve.

Key facts about the levator scapulae muscle
Origins Transverse process of the atlas and axis, posterior tubercles C3 and C4
Insertions Posterior surface of the medial scapular border (from the superior angle to the root of the spine of the scapula)
Innervation Anterior rami of the nerves C3 and C4, dorsal scapular nerve (branch of the C5)
Function Elevation of the scapula

Rhomboid major

Rhomboid major muscle: This is a ribbon like rhomboid shaped muscle that arises from the spinous processes of the T2-T5 (T = thoracic) vertebrae and inserts onto the medial border of the scapula. This muscle primary retracts the scapula, elevates the medial border, and also stabilizes the scapula against the thoracic wall. It is innervated by the posterior scapular nerve.

Rhomboid minor

Rhomboid minor muscle: This is a smaller muscle with the same shape as the rhomboid major and lies above it. It arises from the nuchal ligament and spinous processes of C7 to T1. It inserts onto the medial border of the scapula just superior to the rhomboid major. The actions and innervation are the same as the rhomboid major.

Key facts about the rhomboid muscles
Rhomboid minor

Origins: nuchal ligament, spinous processes of C7 and T1 vertebrae

Insertions: medial end of the scapular spine

Innervation: dorsal scapular nerve

Function: retraction and fixation of the scapula on the thoracic wall

Rhomboid major

Origins: spinous processes of T2 to T5

Insertions: medial border of scapula from the level of the spine to the nferior angle

Innervation: dorsal scapular nerve

Function: retraction and fixation of the scapula on the thoracic wall

Trapezius

Trapezius muscle: This is a superficial, large, fan like muscle found on the back. It arises from the occipital bones, occipital protuberance and nuchal lines, as well as the spinous processes of C7 through T12. It inserts onto the spine of the scapula, acromion, and lateral third of the clavicle. The muscle can be divided into three sets of fibers: upper, middle, and lower. The upper fibers act to extend the neck, elevate, and upwardly rotate. The middle fibers retract (adduct). The lower fibers are responsible for elevation and depression. It is innervated by the C3 & C4 and the accessory nerve (cranial nerve 11 = CN11).

Key facts about the trapezius muscle
Origins Superior nuchal line, external occipital protruberance, nuchal ligament, spinous processes of C7 to T12 vertebrae
Insertions Lateral third of the clavicle, acromion and spine of the scapula
Innervation Spinal accessory nerve; C3 and C4 spinal nerves
Function Elevation, depression, and retraction of the scapula

Shoulder

The shoulder moves at the glenohumeral joint. There are a number of other joints in the region which all move in unison in order to generate a stable movement.

Pectoralis major

Pectoralis major muscle : This is a superficial, large, fan shaped muscle that makes up the bulk of the pectoral (chest) region. It has both sternocostal and clavicular heads. The clavicular head arises from the medial two thirds of the inferior surface of the clavicle. The sternocostal head arises from the sternum and the superior 6-7 costal cartilages.

It inserts onto the lateral lip of the intertubercular sulcus (bicipital groove) of the humerus. The clavicular head enables the muscle to act as a flexor (decrease angle between joints) of arm at the shoulder and the sternocostal head enables the muscle to act as an extensor (increase angle between joints). When the whole muscle acts as a unit it acts as a medial rotator and adductor the arm at the shoulder. It is innervated by the medial (C8-T1) and lateral (C5-C7) pectoral nerves.

Key facts about the pectoralis major muscle
Origins Medial half of the clavicle (clavicular head); anterior surface of the sternum, 1st to 6th costal cartilages, aponeurosis of external oblique muscle (sternocosotal head)
Insertions Intertubercular sulcus of the humerus (lateral lip)
Innervation Lateral and medial pectoral nerves
Function Adduction and medial rotation of the humerus

Pectoralis minor

Pectoralis minor muscle: This muscle lies deep to the pectoralis major and arises from 3rd-5th costals sternal ends and its associated fascia (connective tissue surrounding a muscle group). Pectoralis minor inserts onto the coracoid process of the scapula. This muscle is considered an accessory muscle of respiration.

It acts to draw the scapula lateral, forward, downward, and stabilizes the scapula. It is the prime mover in forward reaching and pushing down. It is innervated by the medial and lateral pectoral nerves.

Key facts about the pectoralis minor muscle
Origins Anterior surface of the 3rd, 4th, and 5th ribs and the fascia overlying the intercostal spaces
Insertions Medial border and superior surface of the coracoid process of the scapula
Innervation Medial pectoral nerve
Function Protraction of the scapula, pulls the coracoid process anteriorly and inferiorly, accessory muscle in respiratory

Deltoid 

Deltoid muscle: This muscle is named due to its Greek delta letter shape (triangular) appearance. It is a powerful superficial muscle of the shoulder. Like the trapezius, this muscle can be divided into three sets of fibers: anterior, lateral, and posterior.

Due to this arrangement the deltoid has a large area of origin: from the acromion, lateral superior portion of the clavicle, and lateral third of the scapular spine. It inserts onto the deltoid tuberosity, which is a roughened elevated patch found on the lateral surface of the humerus. As a result it acts as a flexor, extensor, and abductor of the shoulder. It also assists in medial (anterior fibers) and lateral rotation (posterior fibers). The movements would be used in bowling or swing your arms while walking. It is innervated by the axillary nerve.

Key facts about the deltoid muscle
Origins Lateral third of the clavicle, acromion, and spine of scapula
Insertions Deltoid tuberosity of the humerus
Innervation Axillary nerve
Function Abduction and stabilization of the shoulder joint

Coracobrachialis

Coracobrachialis muscle : The beauty of this muscle is that its name explains its origin, insertion, and action. This deep muscle arises from the coracoid process of the scapula and inserts onto the medial surface of the humeral diaphysis (shaft). It acts as an adductor, medial rotator, and flexor of the arm at the shoulder joint. It is innervated by the musculocutaneous nerve, a branch of the lateral cord of the brachial plexus. It is often grouped as one of the muscles of the arm due to its insertion, but its actions involve the shoulder portion only, this why it has been included in the shoulder section here.

Key facts about the coracobrachialis muscle
Origins Coracoid process of the scapula
Insertions Anteromedial surface of the humerus
Innervation Musculocutaneous nerve
Function Adduction and flexion of the arm

Latissimus dorsi

Latissimus dorsi muscle : This is a large, fan shaped superficial muscle which has a large area of origin. It arises from the spinous processes of the T7-L5 (L = Lumbar) vertebrae, costals 8-12, inferior angle of the scapula, and iliac crest. It blends into the thoracolumbar fascia, which acts to stabilize the sacroiliac joints along with the gluteus maximus muscles. The muscle forms the posterior axillary fold and rotates in order to insert onto the floor of the intertubercular sulcus of the humerus. It is innervated by the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus.

Key facts about the latissimus dorsi muscle
Origins Spinous processes of T7-L5 and sacrum, iliac crest, X-XII ribs
Insertions Intertubercular groove of the humerus
Innervation Thoracodorsal nerve (C6-C8)
Function Contracting insertion->origin: adduction, extension, internal rotation of the arm
Contracting origin->insertion: rotation of the trunk

Arm (Brachium)

The layman will refer to the entire upper limb as the arm. However, the anatomist knows that the ‘arm’ or the ‘brachium’ is purely the region between the shoulder joint and elbow. There are relatively few muscles which its movements and function are easy to learn.

Brachialis

Brachialis muscle: This is the deep primary flexor of the elbow and arises from the lower part of the anterior surface of the humerus. It inserts onto the coronoid process and tuberosity of the ulna. It is innervated by the musculocutaneous nerve.

Key facts about the brachialis muscle
Origins Distal half of the anterior side of the humerus and intermuscular septa
Insertions Coronoid process and ulnar tuberosity
Innervation Musculocutaneous and radial nerves
Function Flexion of the forearm at the elbow joint

Biceps brachii

Biceps brachii muscle: This superficial muscle forms the bulk of the anterior compartment of the arm. It has a long head and a short head. The long head arises from the supraglenoid tubercle of the scapula and passes through the intertubercular sulcus in its own synovial sheath. The short head arises from the coracoid process and both heads unite. The muscle then descends inferiorly to insert into the radial tuberosity of the radius as well as help create the bicipital aponeurosis, an expansion that inserts into the deep fascia of the forearm and onto the ulna. The muscle acts primarily as a supinator of the forearm, as well as a flexor of the elbow. It’s supinating effect are maximal when the elbow is flexed. It is innervated by the musculocutaneous nerve.

Key facts about the biceps brachii muscle
Origins Long head - supraglenoid tubercle of the scapula
Short head - apex of the coracoid process of the scapula
Insertions Radial tuberosity of the radius
Innervation Musculocutaneous nerve
Function Flexion of the forearm at the elbow joint, supinator of the forearm, accessory flexor of the arm at the glenohumeral joint

Triceps brachii

Triceps brachii muscle: This is the only muscle of the posterior compartment of the arm. It has three heads: long, lateral, and medial. The long head arises from the infraglenoid tubercle and consists of mainly type 2b fibers. It allows for powerful elbow extension (such as doing a pushup). The lateral head arises from the posterior surface of the humerus, above the radial groove of the humerus. It consists mainly of type 2a fibers and provides power and endurance to elbow extension. The medial head arises from the posterior surface of the humerus below the radial groove. It consists mainly of type 1 muscle fibers and hence provides sustained elbow extension. All three heads unite and insert onto the olecranon process and fascia of the ulna.  

It is innervated by the radial nerve, a portion of the posterior branch of the brachial plexus.  

Key facts about the triceps brachii muscle
Origins Long head - infraglenoid tubercle of the scapula
Medial head - posterior surface of the humerus
Lateral head - posterior surface of the humerus
Insertions Olecranon
Innervation Radial nerve
Function Extension of the forearm and elbow joint

Forearm Flexors

The forearm is the region between the elbow and the wrist and is composed of an extensor and flexor compartment. The closer we move to the hand the more muscles we begin to have, as our movements require finer and finer gradations. We will study these muscles in depth.

There are numerous muscles in this compartment. The common flexor origin is the medial epicondyle. This compartment is anterior in anatomical position.

Pronator quadratus

Pronator quadratus muscle: In the deepest layer of the forearm is the pronator quadratus, which is found connecting the radius (insertion) and ulna (origin) at their distal points like a strap. It pronates the radius and is innervated by the anterior interosseous branch of the median nerve.

Key facts about the pronator quadratus muscle
Origins Anterior surface of the ulna (distal quarter)
Insertions Anterior surface of the radius (distal quarter)
Innervation Anterior interosseous nerve
Function Forearm pronation and binding of the radius and ulna

Flexor pollicis longus

Flexor pollicis longus muscle: This muscle is found superficially within the deep layer. It arises from the anterior surface of the radius and adjacent interosseous membrane. The tendon of the muscle passes in its own tunnel to enter the palm and it inserts onto the base of the 1st distal phalanx. The tendon is kept close to the bones by a series of flexor tendon sheaths, which lubricate the tendon and prevent bowstringing (excessive loss of proximal pulley). It causes flexion of the interphalangeal joint (IP joint) of the thumb, as well as flexion at the metacarpophalangeal joint (MP joint). It is innervated by the median nerve a branch of the lateral and medial cord of the brachial plexus.

Key facts about the flexor pollicis longus muscle
Origins Anterior surface of the radius and interosseous membrane
Insertions Base of the distal phalanx of the thumb
Innervation Anterior interosseous nerve
Function Flexion of the phalanges of the thumb

Flexor digitorum profundus

F lexor digitorum profundus muscle: It rises from the anterior proximal surface of the ulna and adjacent interosseous membrane and deep fascia of the forearm. It inserts on the distal phalanges of the 2nd to 5th digits and acts to flex the distal IP joints of the fingers.  It also causes contributes to flexion of the proximal IP, MP, and wrist joints, although these are its secondary function. The muscle has dual innervation. The medial head is supplied by the ulnar nerve, and the lateral head by the anterior interosseous branch.

Key facts about the flexor digitorum profundus muscle
Origins Proximal parts of the anterior and lateral surfaces of the ulna and interosseous membrane
Insertions Bases of the phalanges of the 4th and 5th digits (medial part), bases of the phalanges of the 2nd and 3rd digits (lateral part)
Innervation Ulnar nerve (medial part), anterior interosseous nerve (lateral part)
Function Flexion of the distal phalanges at the interphalangeal joints of the 4th and 5th digits (medial part) and of the 2nd and 3rd digits (lateral part)

Flexor digitorum superficialis

Flexor digitorum superficialis muscle: This muscle is located in the intermediate layer and has two heads. The humeroulnar head arises from the medial epicondyle and the radial head arises from the superior anterior surface of the radial shaft. It inserts into the lateral surfaces of the middle phalanges of the 2nd to 5th digits. It divides and allows the tendon of flexor digitorum profundus to pass through at Camper’s chiasm (tendon split). The muscles acts to flex the proximal IP joints as it primary function. It also flexes the MP and wrist joints, although these are its secondary functions. The muscle causes flexion of the wrist, and radial deviation when it acts with extensor carpi radialis. The muscle is innervated by the anterior interosseous branch.

Key facts about the flexor digitorum superficialis muscle
Origins Medial epicondyle of the humerus and coronoid process of the ulna (humero-ulnar head) and superior half of anterior border (ulnar head)
Insertions Shafts of middle phalanges of medial four digits
Innervation Median nerve
Function Flexion of middle phalanges at proximal interphalangeal joints and flexion of the proximal phalanges at the metacarpophalangeal joints of the middle four digits

Flexor carpi radialis and ulnaris

Flexor carpi radialis muscle - cross-sectional view

Flexor carpi muscles:  In the superficial layer of the forearm is where we find flexor carpi radialis, and flexor carpi ulnaris. They both arise from the medial epicondyle, with the radialis inserting onto the base of the 2nd and 3rd metacarpals, and the ulnaris into the pisiform, hook of hamate and base of the 5th metacarpal.  The muscle causes flexion of the wrist and ulnar deviation when its acts with extensor carpi ulnaris. Both of these muscles are innervated by the anterior interosseous branch.

Key facts about the flexor carpi radialis and ulnaris
Flexor carpi radialis muscle

Origins: medial epicondyle of the humerus (common flexor tendon)
Insertions: bases of 2nd metacarpal bone

Innervation: median nerve
Functions: flexion and abduction of the hand at the wrist joint

Flexor carpi ulnaris muscle

Origins: humeral head (medial epicondyle of the humerus), ulnar head (olecranon and posterior border of the ulna)
Insertions: pisiform bone, hook of hamate bone, base of the 5th metacarpal bone

Innervation: ulnar nerve
Functions: flexion and adduction of the hand at the wrist

Palmaris longus

Palmaris longus muscle: This muscle can be absent in some of the population. It lays directly superficial to the flexor digitorum superficialis. It acts as a weak flexor of the wrist and tenses the palmar aponeurosis (fascia) during grip. The palmar aponeurosis helps resist shearing forces applied to the palm, such as climbing and tool use. It is innervated by the anterior interosseous branch.

Key facts about the palmaris longus muscle
Origins Medial epicondyle of the humerus (common flexor tendon)
Insertions Flexor retinaculum and palmar aponeurosis
Innervation Median nerve
Function Flexion of the hand at the wrist joint

Pronator teres

Pronator teres muscle is the larger of the pronator muscles and has two heads. The humeral head arises from the medial supracondylar ridge of the humerus and the coronoid process of the ulna. The muscle inserts onto the anterior lateral surface of the body of the radius. It acts to pronate the forearm and weakly flex the elbow. It is innervated by the median nerve, which passes between its two heads to enter the forearm. The muscle also forms the medial border of the cubital fossa.

Key facts about the pronator teres muscle
Origins Medial epicondyle of the humerus (humeral head), coronoid process of the ulna (ulnar head)
Insertions Lateral side of the radius
Innervation Median nerve
Function Pronation of forearm, flexion of elbow

Forearm Extensors

There are numerous muscles in this compartment as well. The common flexor origin is the lateral epicondyle. This compartment is posterior in anatomical position.

Supinator

Supinator muscle: It is a small muscle that arises from the lateral epicondyle of the humerus, the supinator crest of the ulna, as well as the annular and radial collateral ligaments that support the radius against the ulna. The muscle acts to supinate the forearm and forms the lateral border of the cubital fossa. It is innervated by the deep branch of the radial nerve.

Key facts about the supinator muscle
Origins Lateral epicondyle of the humerus, crest of the ulna, supinator fossa, radial collateral and anular ligaments
Insertions Surface of the proximal third of the radial shaft
Innervation Deep branch of the radial nerve
Function Forearm supination

Extensor digitorum 

Extensor digitorum muscle: This muscle lies in the extensor compartment and arises from the lateral epicondyle. It runs down the posterior compartment of the forearm and inserts into the middle and distal phalanges of the 2nd to 5th digits. It causes extension of the IP joints, the MP joints, and wrist. It also spreads the digits aparts during extension of the MP joints. It is innervated by the posterior interosseous branch.

Key facts about the extensor digitorum muscle
Origins Lateral epicondyle of the humerus
Insertions Posterior surfaces of the middle and distal phalanges (2nd-5th)
Innervation Posterior interosseus nerve (branch of the radial nerve)
Function Extension of the index, middle, ring and little fingers

Extensor carpi ulnaris

Extensor carpi ulnaris muscle: This muscle arises from the lateral epicondyle and runs distally to insert onto the dorsal surface of the base of the 5th metacarpal and ulnar shaft. It acts to extend the wrist, fixes writs during clenching fist, and when it acts with flexor carpi ulnaris it contributes to ulnar deviation of the wrist. It is innervated by the posterior interosseous branch.

Key facts about the extensor carpi ulnaris muscle
Origins Lateral epicondyle of the humerus, posterior border of the ulna
Insertions Medial side of the base of the metacarpal V
Innervation Posterior interosseus nerve (branch of the radial nerve)
Function Extension and adduction of the wrist

Extensor carpi radialis longus and brevis

Extensor carpi radialis longus and brevis muscles: The longus muscle arises from the lateral epicondylar ridge and inserts onto the dorsal surface of the 2nd metacarpal. It acts to extend the wrist and also contributes to radial deviation of the wrist. The brevis muscle arises from the lateral epicondyle and inserts onto the dorsal base of the 3rd metacarpal. It also acts as an extensor of the wrist and radial deviator. Both these muscles are known as the ‘punching muscles’ as they contribute to radial deviation of the wrist, which is essential for boxers. The longus is innervated by the radial nerve and the brevis by the posterior interosseous branch.

Key facts about the extensor radialis longus and brevis muscles
Extensor carpi radialis longus muscle

Origins: Lateral supra-epicondylar bridge of humerus

Insertions: Base of the 2nd metacarpal

Innervation: Radial nerve

Function: Extension and abduction of the hand at the wrist joint

Extensor carpi radialis brevis muscle

Origins: Lateral epicondyle of humerus

Insertions: Base of the 3rd metacarpal

Innervation: Deep branch of radial nerve

Function: Extension and abduction of the hand at the wrist joint

Extensor indicis proprius

Extensor indicis proprius muscle: This muscle arises from the posterior distal 3rd of the ulna and interosseous membrane and inserts onto the middle and distal phalanx of the index finger. It acts to support the extensor digitorum muscle in extending the index finger and wrist. The muscle is innervated by the posterior interosseous branch.

Key facts about the extensor indicis muscle
Origins Posterior side of the distal third of the ulnar shaft; interosseous membrane
Insertions External expansion of the 2nd digit
Innervation Posterior interosseous nerve
Function Extension of the 2nd digit

Extensor digiti minimi

Extensor digiti minimi muscle: This muscle arises from the anterior surface of the lateral epicondyle of the humerus. It inserts into the 5th proximal phalanx (pinky finger). It acts to extend the pinky as well as the wrist. It is innervated by the posterior interosseous branch.

Key facts about the extensor digiti minimi muscle
Origins Lateral epicondyle of the humerus
Insertions Dorsal aponeurosis of the little finger
Innervation Posterior interosseus nerve (branch of the radial nerve)
Function Extension of the little finger

Brachioradialis

Brachioradialis muscle: This muscle lies between the flexor and extensor compartments of the forearm. It arises from the lateral epicondylar ridge and inserts onto the radial styloid process. It acts to flex the elbow. It is also capable of weakly supinating and pronating the forearm. It’s supinating effect are maximal when the elbow is extended. It is innervated by the radial nerve.

Key facts about the brachioradialis muscle
Origins Proximal two-thirds of the supra-epicondylar ridge of the humerus
Insertions Lateral surface of the distal end of the radius
Innervation Radial nerve
Function Forearm flexion, especially during mid-pronation

Hand

The hand is truly the epitome of anatomical complexity. It has numerous muscles and has a complex range of movements. Our opposable thumb is essential to our advancement as a species. The muscles discussed below are essential to everyday life and advanced movements such as writing.

Thenar eminence

Thenar eminence: It consists of three muscle: flexor pollicis brevis, abductor pollicis brevis, and the opponens pollicis. The muscles are named after their functions, with the flexor muscle medial most, the abductor lateral most, and the opponens muscle lying deep. The muscle arises mainly from the flexor retinaculum and tubercle of the trapezium and inserts onto the proximal phalanx or metacarpal of the thumb.

Superficial head of flexor pollicis brevis muscle - ventral view

The flexor pollicis brevis acts to flex the thumb at the 1st MP joint and is innervated by the median nerve. The abductor pollicis brevis acts to abduct the thumb and is also innervated by the median nerve. It arises from the flexor retinaculum, scaphoid tubercle, and trapezium. It inserts onto the radial surface of the 1st proximal phalanx.

Key facts about the flexor pollicis brevis and abductor pollicis brevis muscles
Flexor pollicis brevis

Origin - flexor retinaculum and tubercles of trapezium and scaphoind bones

Insertion - base of the proximal phalanx of the thumb

Innervation - recurrent branch of the median nerve (superficial head) and deep branch of ulnar head (deep head)

Function - thumb flexion (bending)

Abductor pollicis brevis muscle

Origin - flexor retinaculum and tubercles of trapezium  and scaphoind bones

Insertion - base of the proximal phalanx of the thumb

Innervation - recurrent branch of the median nerve

Function - thumb abduction (moving away from the hand

Opponens pollicis acts to oppose the thumb with the other digits (rotation of the thumb to pulp of the other fingers and not just flex across the palm). It arises from the trapezium and transverse carpal ligament. It inserts onto the radial aspect of the 1st metacarpal. It is also innervated by the median nerve.

Key facts about the opponens pollicis muscle
Origins

Flexor retinaculum and tubercle of trapezium  and scaphoid bones

Insertions first metacarpal bone
Innervation Recurrent branch of the median nerve
Function Thumb flexion, abduction, and medial rotation resulting in a combined movement called opposition

Hypothenar eminence

Hypothenar eminence: It consists of the flexor digiti minimi brevis, the abductor digiti minimi brevis, and the opponens digiti minimi. The abductor digiti minimi arises from the pisiform, pisohamate ligament, and flexor retinaculum. It inserts onto the ulnar aspect of the 5th proximal phalanx.

Key facts about the abductor digit minimi muscle
Origins Pisiform
Insertions Base of proximal phalanx of 5th digit
Innervation Deep branch of ulnar nerve
Function Abduction of the 5th digit and flexion assistance of the proximal phalanx

The flexor digiti minimi brevis originates from the hamate bone and inserts onto the ulnar aspect of the base of the 5th proximal phalanx.

Key facts about the flexor digiti minimi muscle
Origins Hook of hamate and flexor retinaculum
Insertions Base of the proximal phalanx of the 5th digit
Innervation Deep branch of ulnar nerve
Function Flexion of the proximal phalanx of the 5th digit

The opponens digiti minimi arises from the hook of hamate and flexor retinaculum. It inserts into the medial aspect of the 5th metacarpal. The muscles are named after their functions, with the flexor muscle lateral most, the abductor medial most, and the opponens muscle lying deep. These are innervated by the ulnar nerve.

Key facts about the hypothenar muscles
Origins Hook of hamate and flexor retinaculum
Insertions Medial border of 5th metacarpal
Innervation Deep branch of ulnar nerve
Function Opposition of the 5th digit

Interossei

Interossei: These are grouped into four dorsal and three palmar interossei and are part of the midpalmar group. The palmar interossei are unipennate, and the dorsal interossei are bipennate. They arise from the metacarpal bones and insert into the extensor hoods of each finger. The dorsal interossei cause abduction of the fingers and the palmar interossei cause adduction of the fingers. All are innervated by the deep branch of the ulnar nerve, which enters the palm through Guyon’s canal, a tunnel formed by the pisiform and hook of hamate.

Key facts about the interossei muscles
Origins Sides of two adjacent metacarpals (dorsal interossei) and palmar surfaces of the 2nd, 4th, 5th metacarpals (palmar interossei)
Insertions Bases of the proximal phalanges via the extensor expansions of the 2nd to 4th digits (dorsal interossei) and 2nd, 4th, and 5th digits (palmar interossei)
Innervation Deep branch of ulnar nerve
Function Abduction of the 2nd to 4th digits (dorsal interossei), adduction of the 2nd, 4th, and 5th digits (palmar interossei), assisting the lumbricals in extension

Lumbricals

Lumbricals: These are ‘worm like’ muscles that originate from the tendons of the flexor digitorum profundus. These insert into the 2nd - 5th proximal phalanges. As the muscles pass anteriorly to the MP joints and insert they cause flexion of the MP joint and extension of the IP joints.

Key facts about the lumbrical muscles
Origins Tendons of the flexor digitorum profundus
Insertions Lateral expansions of the 2nd to 5th digits
Innervation Median nerve (1st and 2nd lumbricals), deep branch of ulnar nerve (3rd and 4th lumbricals)
Function Flexion of the metacarpophalangeal joints and extension of the interphalangeal joints of the 2nd to 4th digits

The radial two lumbricals are innervated by the median nerve and the ulnar two are innervated by the ulnar nerve.

Lumbrical muscles of the hand - ventral view

Clinical Points

Shoulder dislocation

The shoulder joint (glenohumeral joint) is an inherently unstable joint, and thus requires a significant degree of muscular support in the form of the rotator cuff. The shoulder is most unstable in extension and external rotation. It most commonly dislocates anteriorly (95%), and can damage the axillary nerve. Posterior dislocation can occur in epileptics or electric shocks. Inferior dislocations are the least common and make the upper limb appears as if you are holding your upper limb upwards. Manifestations are limited movement of the shoulder and severe pain.

Rotator cuff tear

The rotator cuff is formed by four muscles, supraspinatus, infraspinatus, teres minor, and subscapularis. Tearing most commonly occurs in the tendon of supraspinatus. As the supraspinatus passes under the subacromial arch it is vulnerable to rupture from a bony spur. Supraspinatus tears result in inability to initiate shoulder abduction. A rotator cuff tear presents with general pain with overhead activities and may present with night pain.

Painful arc syndrome

Commonly referred to as impingement syndrome. This is where the rotator cuff muscles become inflamed and ‘impinged’ as they pass through the subacromial space. This can present as pain, weakness and loss of shoulder movement between 60 and 120 degrees of abduction. This happens due to overuse, such as with a competitive swimmer or shotput thrower.

Galeazzi fracture

This is a fracture of the distal third of the radial shaft with dislocation of the distal radioulnar joint. It commonly occurs following a fall onto an outstretched hand (FOSH). Most common manifestations are pain, swelling, and deformity at the joint.

Monteggia fracture

This is a fracture of the proximal third of the ulna with associated dislocation of the proximal radioulnar joint. One common style of the Monteggia fracture is in children where the radial head is dislocated through a forceful pulling on the arm.

Colles fracture

This is a fracture of the distal radius (within two centimetres of the wrist joint) with associated dorsal translocation of the distal fragment. This expression of trauma makes the hand appear to be dorsiflexed. The same fracture that is palmarflexed is referred to as a Smith's fracture making the hand appear as it is coming inward and downward. It commonly follows a FOSH.

Scaphoid fracture

The scaphoid bone forms the floor of the anatomical snuffbox and articulates with the radius at the wrist. A FOSH may fracture the bone. The patient will present with tenderness within the anatomical snuffbox. The blood supply to the bone runs distal to proximal, as the nutrient branch of the radial artery enters at the distal pole, and runs proximally. Avascular necrosis of the proximal segment is a common complication. This necrosis lead to a flattened thenar eminence (thumb mound palmar surface).  

Mallet finger

This injury is commonly called ‘baseball finger’. It is caused by damage to the extensor tendon complex as it inserts onto the distal phalanx of any of the digits. The distal phalanx therefore lies in permanent flexion, and has the appearance of a mallet.

Boutonniere’s deformity

This is a bony deformity of the finger or toes associated with rheumatoid arthritis and trauma to the end of the extended finger. It is caused by proximal interphalangeal joint flexion, and distal interphalangeal joint extension. Resulting in the inability to straighten the digit.

Upper Limb muscles and movements - want to learn more about it?

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Show references

References

  • Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders
  • Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier
  • Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier
  • Monteggia fractures, accessed 19/7/2016
  • Flexor Carpi Ulnaris, accessed 19/7/2016
  • Shoulder "search", accessed 19/7/2016

Article, Review and Layour:

  • Shahab Shahid
  • Franchesca Druggan
  • Adrian Rad

Illustrators:

  • First Illustration Gallery - Yousun Koh
  • Shoulder joint - ventral view - Yousun Koh
  • Infraspinatus muscle - cross-sectional view - National Library of Medicine
  • Serratus anterior muscle - cross-sectional view - National Library of Medicine
  • Levator scapulae muscle - cross-sectional view - National Library of Medicine
  • Rhomboid minor muscle - cross-sectional view - National Library of Medicine
  • Pectoralis major muscle - cross-sectional view - National Library of Medicine
  • Deltoid muscle - cross-sectional view - National Library of Medicine
  • Latissimus dorsi muscle - cross-sectional view - National Library of Medicine
  • Biceps brachii muscle - cross-sectional view - National Library of Medicine
  • Triceps brachii muscle - cross-sectional view - National Library of Medicine
  • Pronator quadratus muscle - cross-sectional view - National Library of Medicine
  • Flexor digitorum profundus muscle - cross-sectional view - National Library of Medicine
  • Flexor carpi radialis muscle - cross-sectional view - National Library of Medicine
  • Pronator teres muscle - cross-sectional view - National Library of Medicine
  • Supinator muscle - cross-sectional view - National Library of Medicine
  • Extensor carpi radialis longus muscle - cross-sectional view - National Library of Medicine
  • Extensor digiti minimi muscle - cross-sectional view - National Library of Medicine
  • Superficial head of flexor pollicis brevis muscle - ventral view - Yousun Koh
  • Lumbrical muscles of the hand - ventral view - Yousun Koh
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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