Upper Limb Nerves

The nerves of the upper limb provide motor, sensory, proprioceptive, and articular innervation to structures extending from the shoulder girdle to the fingertips. Most arise from the brachial plexus, a network formed primarily by the anterior rami of spinal nerves C5-T1.

The five major terminal nerves of the brachial plexus are the musculocutaneous, axillary, radial, median, and ulnar nerves. Additional branches arise from the roots, trunks, and cords of the plexus to supply muscles of the shoulder girdle, thoracic wall, and scapular region.

The course of each nerve is closely related to bones, muscles, fascial compartments, and blood vessels. These anatomical relationships explain characteristic patterns of weakness and sensory loss following nerve injury.

Brachial Plexus

The brachial plexus is formed primarily by the anterior rami of C5, C6, C7, C8, and T1. Variations may include contributions from C4 or T2.

The plexus passes from the neck into the axilla and reorganizes spinal nerve fibers through a sequence of roots, trunks, divisions, cords, and terminal branches.

Organization of the Brachial Plexus

Level	Organization
Roots	C5, C6, C7, C8, T1
Trunks	Superior, middle, inferior
Divisions	Anterior and posterior division from each trunk
Cords	Lateral, posterior, medial
Major terminal nerves	Musculocutaneous, axillary, radial, median, ulnar

Roots of the Brachial Plexus

The roots are the anterior rami of C5-T1. They emerge between the anterior and middle scalene muscles and travel toward the first rib.

Important branches arising directly from the roots include the dorsal scapular nerve and long thoracic nerve.

Trunks of the Brachial Plexus

The roots combine to form three trunks:

• Superior trunk: C5-C6
• Middle trunk: C7
• Inferior trunk: C8-T1

The trunks lie in the lower part of the posterior triangle of the neck before passing toward the clavicle.

Divisions of the Brachial Plexus

Each trunk divides into an anterior and posterior division. These divisions generally redistribute fibers according to the embryological flexor and extensor compartments of the upper limb.

Anterior divisions contribute predominantly to nerves supplying anterior, or flexor, compartments. Posterior divisions contribute predominantly to nerves supplying posterior, or extensor, compartments.

Cords of the Brachial Plexus

The divisions recombine to form the lateral, medial, and posterior cords. The cords are named according to their relationship to the second part of the axillary artery.

Cord	Formation	Major Terminal Contributions
Lateral cord	Anterior divisions of superior and middle trunks	Musculocutaneous nerve and lateral root of median nerve
Medial cord	Anterior division of inferior trunk	Ulnar nerve and medial root of median nerve
Posterior cord	Posterior divisions of all three trunks	Axillary and radial nerves

Major Terminal Nerves

Nerve	Roots	Principal Motor Distribution
Musculocutaneous	C5-C7	Anterior compartment of arm
Axillary	C5-C6	Deltoid and teres minor
Radial	C5-T1	Posterior arm and forearm
Median	C6-T1, sometimes C5 contribution	Most anterior forearm muscles and several intrinsic hand muscles
Ulnar	Primarily C8-T1	Selected anterior forearm muscles and most intrinsic hand muscles

Musculocutaneous Nerve

The musculocutaneous nerve arises from the lateral cord of the brachial plexus and usually contains fibers from C5-C7. It enters the anterior compartment of the arm by piercing coracobrachialis.

It then descends between biceps brachii and brachialis and continues distally as the lateral cutaneous nerve of the forearm.

Motor Supply of the Musculocutaneous Nerve

• Coracobrachialis
• Biceps brachii
• Brachialis

These muscles contribute principally to elbow flexion, while biceps brachii is also a powerful supinator of the forearm.

Sensory Supply of the Musculocutaneous Nerve

After providing its muscular branches, the musculocutaneous nerve continues as the lateral cutaneous nerve of the forearm and supplies skin over the lateral forearm.

Musculocutaneous Nerve Injury

Isolated musculocutaneous nerve injury is relatively uncommon. A lesion can weaken elbow flexion and forearm supination and may reduce sensation over the lateral forearm.

Elbow flexion is not necessarily abolished because other muscles, including brachioradialis, receive innervation from different nerves.

Axillary Nerve

The axillary nerve arises from the posterior cord of the brachial plexus and carries fibers primarily from C5-C6. It passes posteriorly through the quadrangular space with the posterior circumflex humeral vessels.

The nerve then winds around the surgical neck of the humerus deep to the deltoid.

Motor Supply of the Axillary Nerve

• Deltoid
• Teres minor

Deltoid is particularly important for abduction of the arm after the initial phase of movement, while teres minor contributes to lateral rotation of the humerus.

Sensory Supply of the Axillary Nerve

The superior lateral cutaneous nerve of the arm, a branch of the axillary nerve, supplies skin over the inferior portion of the deltoid region.

This small area is commonly used clinically when assessing axillary nerve function.

Axillary Nerve Injury

The axillary nerve is vulnerable in fractures involving the surgical neck of the humerus and in shoulder dislocations. Injury may produce deltoid weakness, impaired arm abduction, and sensory loss over the lateral shoulder region.

Long-standing denervation may cause visible flattening or wasting of the deltoid contour.

Radial Nerve

The radial nerve is the major terminal branch of the posterior cord and contains fibers from C5-T1. It provides the principal motor innervation to the extensor compartments of the arm and forearm.

In the arm, the radial nerve travels posteriorly with the profunda brachii artery and courses along the posterior surface of the humerus within the radial groove.

Radial Nerve in the Arm

The radial nerve supplies triceps brachii and anconeus and gives branches to portions of brachialis and brachioradialis. It also provides cutaneous branches to posterior and lateral regions of the arm and forearm.

After winding around the humerus, it enters the anterior aspect of the distal arm and approaches the lateral epicondylar region.

Radial Nerve at the Elbow

Near the lateral epicondyle, the radial nerve divides into superficial and deep branches. The superficial branch is primarily sensory, while the deep branch is predominantly motor.

The deep branch passes through the supinator muscle and continues as the posterior interosseous nerve.

Posterior Interosseous Nerve

The posterior interosseous nerve is the continuation of the deep branch of the radial nerve after it passes through the supinator. It supplies most of the extensor muscles in the posterior compartment of the forearm.

Because it is predominantly motor, isolated injury typically causes weakness of finger and thumb extension without the large cutaneous sensory deficit expected from a more proximal radial nerve lesion.

Superficial Branch of the Radial Nerve

The superficial radial nerve travels deep to brachioradialis through much of the forearm before becoming superficial near the wrist.

It supplies sensation to part of the dorsolateral hand and proximal dorsal aspects of the lateral digits. The distal fingertips and nail beds of these digits are supplied principally through palmar digital branches of the median nerve.

Motor Supply of the Radial Nerve

The radial nerve and its branches supply muscles responsible for extension at the elbow, wrist, fingers, and thumb, as well as several muscles contributing to forearm and elbow movements.

• Triceps brachii
• Anconeus
• Brachioradialis
• Extensor carpi radialis longus
• Extensor carpi radialis brevis
• Supinator
• Extensor digitorum
• Extensor digiti minimi
• Extensor carpi ulnaris
• Abductor pollicis longus
• Extensor pollicis brevis
• Extensor pollicis longus
• Extensor indicis

Radial Nerve Injury

The deficits caused by radial nerve injury depend strongly on the level of the lesion. Proximal lesions can affect elbow, wrist, finger, and thumb extension, while more distal lesions spare progressively more proximal muscles.

Radial nerve injury associated with the humeral shaft can occur because the nerve lies close to the bone within the radial groove.

Wrist Drop

Loss of effective wrist extensor function can produce wrist drop. The wrist tends to remain flexed because the flexor muscles are no longer adequately opposed by the extensors.

Finger extension may also be impaired depending on the level of radial nerve injury.

Median Nerve

The median nerve is formed by contributions from the lateral and medial cords of the brachial plexus. It commonly contains fibers from C6-T1, with a variable contribution from C5.

The median nerve travels with the brachial artery through much of the arm but normally provides no major motor branches to muscles of the arm.

Median Nerve in the Cubital Fossa

The median nerve enters the cubital fossa medial to the brachial artery and passes into the forearm between the heads of pronator teres.

It then descends through the anterior forearm between muscle layers toward the wrist.

Motor Supply of the Median Nerve in the Forearm

The median nerve supplies most muscles of the anterior compartment of the forearm either directly or through its anterior interosseous branch.

• Pronator teres
• Flexor carpi radialis
• Palmaris longus
• Flexor digitorum superficialis

The anterior interosseous nerve supplies deeper muscles including flexor pollicis longus, pronator quadratus, and the lateral portion of flexor digitorum profundus.

Anterior Interosseous Nerve

The anterior interosseous nerve is a motor branch of the median nerve arising in the proximal forearm. It descends along the anterior interosseous membrane with the anterior interosseous vessels.

It supplies flexor pollicis longus, pronator quadratus, and the portion of flexor digitorum profundus acting on the index and commonly the middle finger.

Median Nerve at the Wrist

The median nerve enters the hand through the carpal tunnel, deep to the flexor retinaculum. Within or shortly beyond the tunnel it divides into branches supplying the thenar region and lateral digits.

The palmar cutaneous branch arises proximal to the flexor retinaculum and passes superficial to it, which is clinically important in carpal tunnel syndrome.

Median Nerve in the Hand

Within the hand, the median nerve supplies several muscles involved in fine thumb movement and the first two lumbricals.

• Abductor pollicis brevis
• Opponens pollicis
• Superficial head of flexor pollicis brevis
• First lumbrical
• Second lumbrical

Recurrent Branch of the Median Nerve

The recurrent branch of the median nerve supplies most of the thenar muscles. Its superficial location in the palm makes it clinically important during injuries and surgical procedures involving the thenar region.

Sensory Supply of the Median Nerve

The median nerve supplies much of the lateral palm and the palmar surfaces of the lateral three and a half digits. Its digital branches also supply the dorsal distal portions and nail beds of these digits.

The exact borders of cutaneous territories overlap with adjacent nerves and vary between individuals.

Carpal Tunnel Syndrome

Carpal tunnel syndrome results from compression of the median nerve within the carpal tunnel. Symptoms commonly include paresthesia, numbness, or pain affecting the median nerve digital distribution.

More advanced compression can impair thenar motor function and produce weakness of thumb opposition and abduction.

Palmar Sensation in Carpal Tunnel Syndrome

Sensation over the central thenar or proximal palmar region may be relatively preserved in isolated carpal tunnel syndrome because the palmar cutaneous branch of the median nerve arises proximal to the tunnel and travels superficial to the flexor retinaculum.

Median Nerve Injury at the Elbow

A proximal median nerve lesion can impair pronation, weaken wrist flexion, interfere with flexion of several digits, and substantially affect thumb function.

Sensory abnormalities can involve the lateral palm and lateral digits.

Anterior Interosseous Nerve Syndrome

Injury to the anterior interosseous nerve produces a predominantly motor deficit because the nerve does not provide cutaneous sensory innervation.

Weakness of flexor pollicis longus and the index component of flexor digitorum profundus can impair the ability to form a normal tip-to-tip pinch between the thumb and index finger.

Ulnar Nerve

The ulnar nerve arises from the medial cord of the brachial plexus and carries fibers predominantly from C8-T1, although contributions can vary.

It descends along the medial arm and passes posterior to the medial epicondyle of the humerus, where it is relatively superficial.

Ulnar Nerve at the Elbow

Behind the medial epicondyle, the ulnar nerve passes through a region where it can be readily compressed or traumatized. It then enters the forearm between the heads of flexor carpi ulnaris.

This superficial relationship explains the familiar tingling sensation that may radiate toward the medial hand after striking the region behind the medial epicondyle.

Motor Supply of the Ulnar Nerve in the Forearm

The ulnar nerve supplies:

• Flexor carpi ulnaris
• Medial portion of flexor digitorum profundus

The medial portion of flexor digitorum profundus primarily flexes the distal interphalangeal joints of the ring and little fingers.

Ulnar Nerve at the Wrist

The ulnar nerve enters the hand superficial to the flexor retinaculum through the region known as Guyon's canal. It then divides into superficial and deep branches.

The superficial branch is predominantly sensory, while the deep branch supplies most of the intrinsic muscles of the hand.

Motor Supply of the Ulnar Nerve in the Hand

The ulnar nerve supplies most intrinsic hand muscles, including:

• Hypothenar muscles
• Palmar interossei
• Dorsal interossei
• Third and fourth lumbricals
• Adductor pollicis
• Deep head of flexor pollicis brevis
• Palmaris brevis

Interossei

The dorsal interossei abduct the fingers away from the axial line through the middle finger, while the palmar interossei adduct the fingers toward this line.

Because both groups are supplied by the deep branch of the ulnar nerve, finger abduction and adduction provide useful clinical tests of ulnar motor function.

Sensory Supply of the Ulnar Nerve

The ulnar nerve supplies sensation to the medial portion of the hand and approximately the medial one and a half digits. Palmar and dorsal cutaneous branches arise at different levels, so the exact sensory deficit varies according to the site of injury.

Ulnar Nerve Injury

The ulnar nerve is particularly vulnerable near the medial epicondyle and at the wrist. Lesions can produce weakness of intrinsic hand muscles, impaired finger abduction and adduction, weakened grip, and sensory abnormalities affecting the medial hand.

Ulnar Claw

Ulnar nerve injury can produce a characteristic posture involving the ring and little fingers, commonly called an ulnar claw. Loss of the medial lumbricals and interossei alters the balance of forces acting across the metacarpophalangeal and interphalangeal joints.

The appearance and severity depend on the level and chronicity of the lesion.

Froment Sign

Froment sign can be used to assess weakness of adductor pollicis due to ulnar nerve dysfunction. When a patient attempts to hold an object between the thumb and index finger, compensatory flexion of the thumb interphalangeal joint may occur through median-innervated flexor pollicis longus.

Long Thoracic Nerve

The long thoracic nerve arises from the roots of the brachial plexus, typically C5-C7. It descends along the lateral thoracic wall and supplies serratus anterior.

Serratus anterior protracts the scapula, holds it against the thoracic wall, and contributes to upward rotation required for full elevation of the upper limb.

Long Thoracic Nerve Injury

Injury to the long thoracic nerve causes weakness or paralysis of serratus anterior and can produce medial scapular winging. The medial border of the scapula becomes prominent, particularly when pushing against a wall.

Dorsal Scapular Nerve

The dorsal scapular nerve commonly arises from the C5 root of the brachial plexus. It supplies the rhomboid muscles and frequently contributes to the innervation of levator scapulae.

These muscles participate in scapular retraction, elevation, and stabilization.

Suprascapular Nerve

The suprascapular nerve arises from the superior trunk, usually carrying fibers from C5-C6. It passes toward the scapula and travels through the suprascapular notch beneath the superior transverse scapular ligament.

It supplies supraspinatus and infraspinatus and provides articular branches to the shoulder region.

Motor Functions of the Suprascapular Nerve

Supraspinatus contributes to initiation of arm abduction, while infraspinatus is an important lateral rotator of the humerus.

Suprascapular nerve injury can therefore impair both movements.

Lateral Pectoral Nerve

The lateral pectoral nerve arises from the lateral cord and carries fibers mainly from C5-C7. It supplies pectoralis major and communicates with the medial pectoral nerve.

Medial Pectoral Nerve

The medial pectoral nerve arises from the medial cord, usually carrying fibers from C8-T1. It supplies pectoralis minor and contributes to the innervation of pectoralis major.

Upper and Lower Subscapular Nerves

The upper and lower subscapular nerves arise from the posterior cord. The upper subscapular nerve supplies subscapularis, while the lower subscapular nerve supplies subscapularis and teres major.

Thoracodorsal Nerve

The thoracodorsal nerve arises from the posterior cord, usually carrying fibers from C6-C8, and supplies latissimus dorsi.

Latissimus dorsi extends, adducts, and medially rotates the humerus.

Medial Cutaneous Nerve of the Arm

The medial cutaneous nerve of the arm arises from the medial cord and supplies skin over portions of the medial arm. It commonly communicates with the intercostobrachial nerve.

Medial Cutaneous Nerve of the Forearm

The medial cutaneous nerve of the forearm arises from the medial cord and provides cutaneous innervation to the medial forearm through anterior and posterior branches.

Major Nerves by Upper Limb Compartment

Compartment or Region	Principal Nerve
Anterior arm	Musculocutaneous nerve
Posterior arm	Radial nerve
Anterior forearm	Median nerve, with ulnar nerve contribution
Posterior forearm	Radial nerve and posterior interosseous nerve
Thenar region	Predominantly median nerve
Interossei	Ulnar nerve
Most intrinsic hand muscles	Ulnar nerve
Deltoid	Axillary nerve

Cutaneous Innervation of the Upper Limb

Cutaneous sensation is distributed among branches of the brachial plexus and neighboring thoracic nerves. Peripheral nerve territories should be distinguished from dermatomes because named peripheral nerves contain fibers from multiple spinal nerve levels.

Nerve	Representative Sensory Territory
Axillary	Lateral shoulder over inferior deltoid
Musculocutaneous	Lateral forearm
Radial	Posterior arm and forearm, dorsolateral hand
Median	Lateral palm and lateral three and a half digits
Ulnar	Medial hand and medial one and a half digits
Medial cutaneous nerve of arm	Medial arm
Medial cutaneous nerve of forearm	Medial forearm

Autonomous Sensory Zones

Because cutaneous nerve territories overlap, small regions with relatively little overlap are often selected during neurological examination.

Nerve	Commonly Tested Region
Axillary	Skin over lateral deltoid
Musculocutaneous	Lateral forearm
Radial	Dorsal first web-space region
Median	Palmar surface of index fingertip
Ulnar	Palmar surface of little fingertip

Dermatomes of the Upper Limb

A dermatome represents a cutaneous territory associated primarily with a spinal nerve root rather than a named peripheral nerve.

Root	Commonly Tested Region
C5	Lateral upper arm
C6	Lateral forearm and thumb
C7	Middle finger region
C8	Little finger and medial distal forearm
T1	Medial forearm
T2	Upper medial arm and axillary region

Dermatome boundaries overlap and vary among individuals and anatomical maps.

Myotomes of the Upper Limb

Clinical examination can use representative movements to assess major cervical spinal root contributions.

Movement	Important Root Contribution
Shoulder abduction	C5
Elbow flexion	C5-C6
Wrist extension	C6-C7
Elbow extension	C7-C8
Finger flexion	C8
Finger abduction and adduction	T1

Peripheral Nerve Territory Versus Dermatome

Feature	Peripheral Nerve	Dermatome
Represents	Distribution of named nerve	Distribution associated with spinal root
Spinal levels	Usually multiple	Primarily one
Clinical importance	Peripheral nerve localization	Radiculopathy localization

Reflexes of the Upper Limb

Deep tendon reflexes assess the integrity of sensory pathways, spinal cord segments, motor neurons, and peripheral nerves.

Reflex	Major Roots	Peripheral Nerve
Biceps reflex	C5-C6	Musculocutaneous nerve
Brachioradialis reflex	C5-C6	Radial nerve
Triceps reflex	C7-C8, principally C7	Radial nerve

Brachial Plexus Injury

Injury to the brachial plexus can occur at different anatomical levels, including roots, trunks, divisions, cords, or terminal branches. The resulting deficits depend on which fibers are affected.

Because individual peripheral nerves contain fibers redistributed from several spinal roots, plexus lesions can produce patterns that differ from both isolated root lesions and isolated terminal nerve injuries.

Upper Trunk Injury

Injury involving the superior trunk, particularly C5-C6 fibers, can affect muscles responsible for shoulder abduction, lateral rotation, and elbow flexion.

This pattern is classically associated with Erb-Duchenne palsy, although the exact neurological deficit depends on the extent of injury.

Lower Trunk Injury

Injury involving the inferior trunk, particularly C8-T1 fibers, can disproportionately affect intrinsic hand muscles and other structures supplied by lower plexus fibers.

Severe lower plexus injury may produce marked weakness of fine hand movements.

Root Lesion Versus Peripheral Nerve Lesion

A spinal nerve root lesion typically produces weakness across muscles supplied by several peripheral nerves but sharing the same root contribution. A peripheral nerve lesion produces deficits concentrated among muscles and cutaneous territories supplied by that named nerve.

This distinction is central to neurological localization.

Common Sites of Upper Limb Nerve Injury

Nerve	Important Vulnerable Site	Possible Major Deficit
Axillary	Surgical neck of humerus	Weak shoulder abduction
Radial	Radial groove of humerus	Wrist and finger extension weakness
Median	Carpal tunnel	Median sensory symptoms and thenar weakness
Ulnar	Medial epicondyle or cubital tunnel	Intrinsic hand weakness
Long thoracic	Lateral thoracic wall	Scapular winging

Nerve Supply and Upper Limb Movements

Movement	Major Nerves Involved
Shoulder abduction	Suprascapular and axillary nerves
Elbow flexion	Musculocutaneous nerve, with radial contribution through brachioradialis
Elbow extension	Radial nerve
Forearm pronation	Median nerve
Forearm supination	Musculocutaneous and radial nerves
Wrist extension	Radial nerve
Finger abduction and adduction	Ulnar nerve
Thumb opposition	Median nerve

Articular Innervation

Upper limb peripheral nerves also provide sensory branches to joints. These articular branches contribute proprioceptive and nociceptive information from joint capsules and related structures.

Joint innervation often reflects the nerves supplying muscles that move the joint, a relationship commonly associated with Hilton's law.

Shoulder Joint Innervation

The glenohumeral joint receives articular branches from several nerves, particularly the axillary and suprascapular nerves, with additional contributions that may vary.

Elbow Joint Innervation

The elbow joint receives articular innervation from branches associated with the musculocutaneous, radial, median, and ulnar nerves.

Wrist and Hand Joint Innervation

The wrist and hand joints receive articular branches from the median, ulnar, radial, and interosseous nerves. Their contributions vary according to the specific joint and region.

Autonomic Fibers in Upper Limb Nerves

Peripheral nerves of the upper limb also carry postganglionic sympathetic fibers. These fibers regulate structures such as cutaneous blood vessels, sweat glands, and arrector pili muscles.

They reach the upper limb through spinal nerves and are distributed distally within branches of the brachial plexus.

Nerve Regeneration

Peripheral nerve axons have some capacity for regeneration following injury if the neuronal cell body survives and an appropriate pathway remains available. The success of recovery depends on the type of nerve injury, distance to the target, integrity of connective tissue pathways, and other biological factors.

Severe injuries that disrupt the nerve's structural framework may require surgical repair and can have incomplete functional recovery.

Electrodiagnostic Assessment

Nerve conduction studies and electromyography can help evaluate peripheral nerve injuries. These tests provide information about nerve conduction, muscle activation, denervation, and reinnervation.

Electrodiagnostic findings are interpreted together with anatomical knowledge and clinical examination to localize lesions.

Clinical Examination of Upper Limb Nerves

Assessment of upper limb nerve function combines motor testing, sensory examination, reflexes, and observation of muscle bulk. Individual movements can be selected to emphasize particular nerves or spinal roots.

Nerve	Representative Motor Test	Representative Sensory Test
Musculocutaneous	Elbow flexion	Lateral forearm
Axillary	Shoulder abduction	Lateral deltoid region
Radial	Wrist or finger extension	Dorsal first web-space region
Median	Thumb opposition or abduction	Index fingertip
Ulnar	Finger abduction	Little fingertip

Key Anatomical Relationships

Nerve	Important Anatomical Relationship
Axillary	Winds around surgical neck of humerus
Radial	Travels in radial groove of humerus
Musculocutaneous	Pierces coracobrachialis
Median	Passes through carpal tunnel
Ulnar	Passes posterior to medial epicondyle
Suprascapular	Passes through suprascapular notch beneath superior transverse scapular ligament
Long thoracic	Descends superficially along lateral thoracic wall

Summary of Major Terminal Nerve Functions

Nerve	Major Motor Role	Representative Sensory Region
Musculocutaneous	Elbow flexion and contribution to supination	Lateral forearm
Axillary	Shoulder abduction	Lateral shoulder
Radial	Extension of elbow, wrist, fingers, and thumb	Posterior limb and dorsolateral hand
Median	Forearm pronation, many wrist and digit flexors, thenar function	Lateral palm and lateral digits
Ulnar	Most intrinsic hand movements and selected forearm flexors	Medial hand and medial digits

Functional Importance

The nerves of the upper limb connect the cervical spinal cord with the muscles, joints, and skin of the shoulder, arm, forearm, and hand. The brachial plexus redistributes fibers from C5-T1 into peripheral nerves specialized for different anatomical compartments and functions.

The musculocutaneous nerve predominantly supplies the anterior arm, the radial nerve supplies the extensor compartments, the median nerve supplies most anterior forearm muscles and important thenar muscles, and the ulnar nerve supplies most intrinsic muscles of the hand. The axillary nerve provides essential innervation to the deltoid and teres minor.

The close relationships between nerves and skeletal landmarks create clinically important sites of vulnerability. The axillary nerve is associated with the surgical neck of the humerus, the radial nerve with the radial groove, the ulnar nerve with the medial epicondyle, and the median nerve with the carpal tunnel.

Understanding upper limb nerves is therefore fundamental to the study of muscle innervation, brachial plexus anatomy, upper limb compartments, hand function, dermatomes, myotomes, reflexes, peripheral nerve injuries, carpal tunnel syndrome, wrist drop, ulnar neuropathy, scapular winging, and neurological localization.