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.
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.
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: 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.
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. 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 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).
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.
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.
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.
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.
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 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.
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 and elevation and depression. It is innervated by the C3 & C4 and the accessory nerve (cervical nerve 11 = CN11).
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 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.
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.
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.
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.
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.
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 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.
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.
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.
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 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.
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.
Flexor digitorum profundus
Flexor 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.
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.
Flexor carpi radialis and ulnaris
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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: 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. 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. 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.
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. The flexor digiti minimi brevis originates from the hamate bone and inserts onto the ulnar aspect of the base of the 5th proximal phalanx. 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.
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.
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. The radial two lumbricals are innervated by the median nerve and the ulnar two are innervated by the ulnar nerve.