Upper Limb Muscle – Anatomy, Nerve Supply, Function

The Upper Limb Muscle comprises many muscles that are organized into anatomical compartments. These muscles act on the various joints of the hand, arm, and shoulder, maintaining tone, providing stability and allowing precise fluid movement.

Axioappendicular groups of muscles arise from the axial skeleton to act upon the pectoral girdle. Scapulohumeral muscles originate from the scapula and insert into the proximal humerus. Included in this category are the rotator cuff muscles which provide stability to the glenohumeral joint. In the arm, the muscles of the anterior compartment are involved in flexion of the forearm, and the posterior comprises of the forearm extensors. Similarly, the anterior compartment of the forearm contains the flexors of the hand and posterior has extensors. The hand is divided into the thenar, the hypothenar, the adductor compartment, as well as the short muscles of the hand.[rx][rx][rx][rx]

Structure of Upper Limb Muscle

Shoulder and Upper limb muscles are specialized to perform functions of pressure and manipulation of objects. Skeletal muscle is formed by myofibers which contain millions of myofibrils, and each of them is formed by sarcomeres. Sarcomeres are the contractile unit, therefore skeletal muscle fibers are completely dedicated to generating force. Skeletal muscle also carries out multiple functions such as voluntary locomotion, the protection of internal organs, generation of heat, and assisting in postural behavior. [rx][rx]

The muscle mass relies on the balance between synthesis and degradation of proteins, the regulation of this process is sensitive to several factors such as nutritional status, hormone levels, physical activity, underlying diseases, injuries, among others.[rx]

Blood Supply of Upper Limb Muscle

The arterial supply to the muscles of the upper limb is primarily from the axillary artery (of subclavian artery) and its branches. The brachial artery supplies to the anterior compartment of the arm, and the profunda brachii supplies the posterior. In the arm, the radial artery supplies the lateral forearm and the ulnar is responsible for the medial aspect. Beyond the wrist, the radial and ulnar arteries form the superficial and deep palmar arterial arches. The deoxygenated blood drains into the cephalic vein and the basilic vein. Lymphatics of the right upper limb drain into the right lymphatic duct, and the left drains into the thoracic duct.[rx][rx][rx]

Nerves of Upper Limb Muscle

The innervation of the muscles of the upper limb is through branches of the brachial plexus which is composed of the ventral rami of C5 through T1 nerve roots.[rx][rx]

• Function: Retraction of scapula and depression of glenoid cavity
• Origin: Spinous processes of T2 through T5 vertebrae
• Insertion: Inferior aspect of medial scapula
• Innervation: Dorsal scapular nerve (C4, C5)

Rhomboid minor

• Function: Retraction of scapula and depression of glenoid cavity
• Origin: Nuchal ligament as well as spines of C7 and T1 vertebrae
• Insertion: Superior aspect of medial scapula
• Innervation: Dorsal scapular nerve (C4, C5)

Scapulohumeral (Intrinsic Shoulder Muscles)

Deltoid

• Function: Anterior part: flexion and medial rotation of arm, middle part: abduction of arm, posterior part: extension and lateral rotation of arm
• Origin: Lateral clavicle, acromion and scapular spine
• Insertion: Deltoid tuberosity
• Innervation: Axillary nerve (C5, C6)

Teres major

• Function: Adduction and medial rotation of arm
• Origin: Posterior surface of  scapula at its inferior angle
• Insertion: Intertubercular groove on its medial aspect
• Innervation: Lower scapular nerve (C5, C6)

Supraspinatus

• Function: Initiation of arm abduction
• Origin: Posterior scapula, superior to the scapular spine
• Insertion: Superior aspect of the greater tubercle
• Innervation: Suprascapular nerve (C5, C6)
• Part of rotator cuff muscles

Infraspinatus

• Function: Lateral rotation of arm
• Origin: Posterior scapula, inferior  to the scapular spine
• Insertion: Greater tubercle of humerus, between supraspinatus and teres minor insertion
• Innervation: Suprascapular nerve (C5, C6)
• Part of rotator cuff muscles

Teres minor 

• Function: Lateral rotation of arm
• Origin: Posterior surface of scapula at its inferior angle
• Insertion: Inferior aspect of the greater tubercle
• Innervation: Axillary nerve (C5, C6)
• Part of rotator cuff muscles

Subscapularis

• Function: Adduction and medial rotation of the arm
• Origin: Anterior aspect of scapula
• Insertion: Lesser tubercle of humerus
• Innervation: Subscapular nerves (C5, C6, C7)
• Part of rotator cuff muscles

*Rotator cuff muscles: supraspinatus, infraspinatus, teres minor, subscapularis

Muscles of Anterior Compartment of Arm (Flexors of Arm)

Biceps brachii

• Function: Major flexion of forearm, supination of forearm, resists dislocation of shoulder
• Origin: Short head originates from the coracoid process. The long head is from the supraglenoid tubercle of scapula
• Insertion: Radial tuberosity and forearm fascia (as bicipital aponeurosis)
• Innervation: Musculocutaneous nerve (C5, C6)

Brachialis

• Function: Flexion of forearm
• Origin: Distal anterior humerus
• Insertion: Coronoid process and ulnar tuberosity
• Innervation:  musculocutaneous nerve (C5, C6, C7 small contribution)

Coracobrachialis

• Function: Flexion and adduction of arm
• Origin: Coracoid process
• Insertion: Middle of the humerus, on its medial aspect
• Innervation: Musculocutaneous nerve (C5, C6, C7)

Muscles of Posterior Compartment of Arm (Extensors of Arm)

Triceps brachii

• Function: Major extensor of forearm, resists dislocation of shoulder
• Origin: Lateral head: above the radial groove, medial head: below the radial groove, long head: infraglenoid tubercle of scapula
• Insertion: Olecranon process of ulna and  forearm fascia
• Innervation: Radial nerve (C6,C7,C8)

Anconeus

• Function: Extension of forearm, stabilization of elbow joint
• Origin: Lateral epicondyle of humerus
• Insertion: Olecranon process and posterior ulna
• Innervation: Radial nerve (C7, C8, T1)

Muscles of Anterior Compartment of Forearm (Flexors of Forearm)

Superficial layer

Pronator teres

• Function: Pronation of radio-ulnar joint
• Origin: Coronoid process and medial epicondyle of humerus
• Insertion: Lateral surface of the radius
• Innervation: Median nerve (C6, C7)

Flexor carpi radialis

• Function: Flexion and adduction at the wrist
• Origin: Medial epicondyle of humerus
• Insertion: Base of second metacarpal
• Innervation: Median nerve (C6, C7)

Palmaris longus

• Function: Flexion at the wrist, tensing of the palmaris aponeurosis
• Origin: Medial epicondyle of humerus
• Insertion: Flexor retinaculum
• Innervation: Median nerve (C7, C8)

Flexor carpi ulnaris

• Function: Flexion and adduction at the wrist
• Origin: Medial epicondyle of humerus and olecranon
• Insertion: Pisiform, hook of hamate and fifth metacarpal
• Innervation: Median nerve (C7, C8)

Intermediate Layer

Flexor digitorum superficialis

• Function: Flexion of the proximal interphalangeal joint of the second, third, fourth, and fifth finger. Also has a weaker flexion action on the metacarpophalangeal joints of the same fingers
• Origin: Medial epicondyle, coronoid process, and anterior radius
• Insertion: Second, third, fourth, and fifth middle phalanges
• Innervation: Median nerve (C7, C8, T1)

Deep Layer

Flexor digitorum profundus

• Function: Flexion of the distal interphalangeal joint of the second, third, fourth, and fifth finger
• Origin: Medial and anterior surface of proximal ulna and interosseous membrane
• Insertion: Second, third, fourth, and fifth distal phalanges
• Innervation: Ulnar nerve (C8, T1) for the medial part, anterior interosseous nerve (C8,T1) for the lateral

Flexor pollicis longus

• Function: Flexion of the interphalangeal joint of the thumb
• Origin: Anterior aspect of radius as well as interosseous membrane
• Insertion: Base of distal phalanx of thumb
• Innervation: Anterior interosseous nerve (C7, C8)

Pronator quadratus

• Function: Pronator of forearm
• Origin: Anterior aspect of distal ulna
• Insertion: Anterior aspect of distal radius
• Innervation: Anterior interosseous nerve (C7, C8)

Brachioradialis

• Function: Weak flexor of the forearm
• Origin: Proximal supracondylar ridge on humerus
• Insertion: Lateral surface of distal end of radius
• Innervation: Radial nerve (C5, C6, C7)

Muscles of Posterior Compartment of Forearm

Superficial

Extensor carpi radialis longus

• Function: Extension and abduction of the wrist
• Origin: Proximal supracondylar ridge on humerus
• Insertion: Dorsal base of second metacarpal
• Innervation: Radial nerve (C6, C7)

Extensor carpi radialis brevis

• Function: Extension and abduction of the wrist
• Origin: Lateral epicondyle of humerus
• Insertion: Dorsal base of third metacarpal
• Innervation: Deep branch of the radial nerve (C7, C8)

Extensor digitorum

• Function: Extension of the proximal interphalangeal joint of the second, third, fourth, and fifth finger. Also has a weaker extension action on the metacarpophalangeal joints of the same fingers
• Origin: Lateral epicondyle of humerus
• Insertion: Extensor expansions on dorsal aspect of second, third, fourth, and fifth middle and distal phalanges
• Innervation: Posterior interosseous nerve (C7, C8)

Extensor digiti minimi

• Function: Extension of the little finger at metacarpophalangeal joint and interphalangeal joint
• Origin: Lateral epicondyle of humerus
• Insertion: Extensor expansion on dorsal aspect of fifth phalanx
• Innervation: Posterior interosseous nerve (C7, C8)

Extensor carpi ulnaris

• Function: Extension and adduction of the wrist
• Origin: Lateral epicondyle of humerus and posterior ulna
• Insertion: Fifth metacarpal base
• Innervation: Posterior interosseous nerve (C7, C8)

Deep Layer

Extensor indicis

• Function: Extension of the index finger
• Origin: Dorsal surface of distal ulna and interosseous membrane
• Insertion: Extensor expansion of second finger
• Innervation: Posterior interosseous nerve (C7, C8)

Supinator

• Function: Supination of the forearm
• Origin: Lateral epicondyle and supinator crest of ulna
• Insertion: Lateral surface of radius
• Innervation: Deep branch of radial nerve (C7, C8)

Abductor pollicus longus

• Function: Abduction of the thumb by acting on the carpometacarpal joint and the metacarpophalangeal joint
• Origin: Dorsal aspects of proximal radius, ulna, and interosseous membrane
• Insertion: Base of first metacarpal
• Innervation: Posterior interosseous nerve (C7, C8)

Extensor pollicus longus

• Function: Extension of the thumb by acting on the carpometacarpal joint, the metacarpophalangeal joint, and the interphalangeal joint.
• Origin: Dorsal aspects of middle ulna and interosseous membrane
• Insertion: Distal phalanx of 1st finger
• Innervation: Posterior interosseous nerve (C7, C8)

Extensor pollicus brevis

• Function: Extension of the thumb by acting on the carpometacarpal joint and the metacarpophalangeal joint
• Origin: Dorsal aspects of middle radius and interosseous membrane
• Insertion: Distal phalanx of 1st finger
• innervation: Posterior interosseous nerve (C7, C8)

Intrinsic Muscles of Hand

Thenar muscles

Opponens pollicus

• Function: Opposition of the thumb
• Origin: Flexor retinaculum  and tubercle of trapezium
• Insertion: Lateral aspect of first metacarpal
• Innervation: Recurrent branch of median nerve (C8, T1)

Abductor pollicus brevis

• Function: Abduction of the thumb at the metacarpophalangeal joint
• Origin: Flexor retinaculum  and tubercle of scaphoid
• Insertion: Lateral aspect of proximal phalanx of first finger
• Innervation: Recurrent branch of median nerve (C8, T1)

Flexor pollicus brevis

• Function: Flexion of the thumb at the metacarpophalangeal joint
• Origin: Flexor retinaculum  and tubercle of trapezium
• Insertion: Lateral aspect of proximal phalanx of first finger
• Innervation: Recurrent branch of median nerve (C8, T1)

Adductor Compartment

Adductor pollicus

• Function: Adduction of the thumb
• Origin: Second, third metacarpal, and capitate
• Insertion: Proximal phalanx and extensor expansion of 1st finger
• Innervation: Deep branch of ulnar nerve (C8, T1)

Hypothenar Muscles

Abductor digiti minimi

• Function: Abduction of the little finger at the metacarpophalangeal joint
• Origin: Pisiform
• Insertion: Medial aspect of proximal phalanx of fifth finger
• Innervation: Deep branch of ulnar nerve (C8, T1)

Flexor digiti minimi brevis

• Function: Flexion of the little finger at the metacarpophalangeal joint
• Origin: Flexor retinaculum and hook of hamate
• Insertion: Medial aspect of proximal phalanx of fifth finger
• Innervation: Deep branch of ulnar nerve (C8, T1)

Opponens digiti minimi

• Function: Opposition of the little finger
• Origin: Flexor retinaculum and hook of hamate
• Insertion: Medial aspect of fifth metacarpal
• Innervation: Deep branch of ulnar nerve (C8, T1)

Short Muscles

Lumbricals

• Function: Flexion of the metacarpophalangeal joints with extension of the interphalangeal joints
• Origin: Arise from tendons of flexor digitorum profundus. First 2 are unipennate, and the third and fourth are bipennate
• Insertion: Extensor expansions of second, third, fourth, and fifth finger
• Innervation: Median nerve (C8, T1) for the lateral 2 lumbricals, deep branch of ulnar nerve (C8, T1) for the medial 2 lumbricals

Dorsal interossei

• Function: Abduction of the second, third, and fourth finger away from the axial line
• Origin: Adjacent metacarpals
• Insertion: Extensor expansions and proximal phalanges of the second, third, and fourth fingers
• Innervation: Deep branch of ulnar nerve (C8, T1)

Palmar interossei

• Function: Adduction of the second, third, and fourth finger towards the axial line
• Origin: Palmar surfaces of second, fourth, and fifth metacarpals
• Insertion: Extensor expansions and proximal phalanges of the second, fourth, and fifth fingers
• Innervation: Deep branch of ulnar nerve (C8, T1)

References