Upper Limb Anatomy — Ultra Notes

Table of contents

Osteology & bony landmarks
Pectoral girdle & scapular muscles
Rotator cuff
Arm muscles
Forearm — flexor-pronator group
Forearm — extensor-supinator group
Intrinsic muscles of the hand
Brachial plexus & peripheral nerves
Arterial supply & regional spaces
Joints & ligaments
Carpal bones, carpal tunnel, snuffbox & compartments

1. Osteology & bony landmarks

High-yield summary

The upper limb skeleton is the clavicle and scapula (pectoral girdle), the humerus (arm), the radius and ulna (forearm), and the eight carpals, five metacarpals and fourteen phalanges (hand). Almost every muscle question in this bank resolves to a named bony landmark, so the osteology is the scaffold on which origins and insertions hang. The clavicle is the only bony strut linking the axial skeleton to the limb; the scapula floats on muscle over the posterior thorax; and the humerus, radius and ulna carry a set of grooves and tuberosities that name-check the nerves and tendons crossing them.

Clavicle

S-shaped strut; medial two-thirds convex forwards, lateral one-third convex backwards. The junction of these curves is the weakest point and the commonest fracture site.
Medial (sternal) end articulates with the manubrium at the sternoclavicular joint; lateral (acromial) end articulates with the acromion at the acromioclavicular joint.
Inferior surface landmarks: conoid tubercle and trapezoid line (coracoclavicular ligament), subclavian groove (subclavius), and the impression for the costoclavicular ligament medially.

Scapula

Flat triangular bone spanning ribs 2–7. Key landmarks: spine, acromion, coracoid process, glenoid cavity, supraglenoid and infraglenoid tubercles, suprascapular notch, and the supraspinous/infraspinous/subscapular fossae.
Three angles (superior, inferior, lateral) and three borders (medial/vertebral, lateral/axillary, superior). The medial border and inferior angle are the palpable landmarks for winging.

Humerus

Proximal: head, anatomical neck, surgical neck (axillary nerve and posterior circumflex humeral artery at risk), greater and lesser tuberosities separated by the intertubercular (bicipital) groove.
Shaft: deltoid tuberosity laterally; the radial (spiral) groove runs obliquely across the posterior surface.

The radial (spiral) groove transmits the radial nerve and the profunda brachii (deep brachial) artery. A mid-shaft humeral fracture therefore threatens the radial nerve here, producing wrist drop with sparing of triceps if the injury is distal to its motor branches.
Distal: capitulum (lateral, articulates with radial head), trochlea (medial, articulates with trochlear notch of ulna), medial and lateral epicondyles, and the radial, coronoid and olecranon fossae. The medial epicondyle carries the ulnar nerve in its groove ("funny bone").

Radius and ulna

Radius: head, neck, radial tuberosity (biceps brachii insertion), shaft, and distal end with the dorsal (Lister's) tubercle, styloid process and ulnar notch.
Ulna: olecranon, coronoid process, trochlear notch, radial notch, tuberosity of ulna (brachialis), shaft, and distal head with styloid process.

Carrying angle

The carrying angle is the lateral (valgus) angle between the long axis of the arm and the long axis of the fully extended, supinated forearm. Normal values are roughly 5–15° in men and 10–25° in women (wider in females). It is created by the asymmetric trochlea (the medial trochlear flange projects more distally) and disappears in flexion and pronation. An increased angle is cubitus valgus (classically after lateral condyle non-union, risking tardy ulnar nerve palsy); a reduced/reversed angle is cubitus varus ("gunstock deformity", classically after supracondylar malunion).

The Edge

Wrist drop from a spiral-groove radial nerve lesion spares the elbow extensors when the fracture is distal to the triceps branches — a mid-shaft break gives weak brachioradialis and wrist/finger drop but an intact triceps jerk.
The bicipital groove points to the lesser tuberosity medially and greater tuberosity laterally: the tendon of latissimus dorsi inserts in the floor, teres major on the medial lip, pectoralis major on the lateral lip ("a lady between two majors").

Clinical relevance (Moore's): The surgical neck of the humerus is the commonest site of proximal fracture and lies against the axillary nerve and posterior circumflex humeral artery, so a fracture or anterior shoulder dislocation there denervates deltoid (loss of abduction) and numbs the regimental-badge patch; a mid-shaft spiral-groove fracture instead endangers the radial nerve, and a childhood supracondylar fracture threatens the median nerve and brachial artery. [Moore, Clinically Oriented Anatomy]

2. Pectoral girdle & scapular muscles

High-yield summary

The girdle muscles anchor the scapula and clavicle to the axial skeleton and set the position of the glenoid so the arm can be used overhead. They fall into anterior (pectoralis major and minor, subclavius, serratus anterior) and posterior (trapezius, levator scapulae, rhomboids, latissimus dorsi) groups, plus the deltoid and teres major that act on the humerus. Scapular control — protraction by serratus anterior and upward rotation by the serratus/trapezius force couple — is the exam's favourite functional theme, and the three intermuscular spaces of the posterior scapular region (triangular space, quadrangular space, triangular interval) transmit named neurovascular bundles.

Anterior girdle muscles

Muscle	Origin	Insertion	Nerve (root)	Action
Pectoralis major (clavicular head)	Medial half of clavicle	Lateral lip of intertubercular groove of humerus	Lateral pectoral nerve (C5–C7)	Flexes and adducts, medially rotates arm
Pectoralis major (sternocostal head)	Sternum, upper 6 costal cartilages, external oblique aponeurosis	Lateral lip of intertubercular groove (fibres "twist" so lower fibres insert higher)	Lateral and medial pectoral nerves (C6–T1)	Adducts and medially rotates; extends from flexed position
Pectoralis minor	3rd–5th ribs near costochondral junctions	Coracoid process of scapula (medial border, superior surface)	Medial pectoral nerve (C8–T1)	Protracts/depresses scapula; stabilises against thoracic wall
Subclavius	1st rib at costochondral junction	Subclavian groove of inferior clavicle	Nerve to subclavius (C5–C6)	Depresses/steadies clavicle; protects subclavian vessels
Serratus anterior	Outer surfaces of ribs 1–8/9	Costal (deep) surface of medial border of scapula	Long thoracic nerve (C5–C7)	Protracts scapula; upward rotation; holds scapula to chest wall

Pectoralis major has two heads — a clavicular head (from the medial clavicle) and a sternocostal head (from the sternum, upper costal cartilages and external oblique aponeurosis). Because the fibres twist ~180° before insertion, the clavicular head aids flexion while the sternocostal head is the prime power for extension of the flexed arm and for adduction against resistance (the climbing/throwing muscle).

Both heads converge to a bilaminar tendon that inserts on the lateral lip of the intertubercular (bicipital) groove of the humerus. Distractors of the medial lip (teres major) and floor (latissimus dorsi) are the classic near-neighbours.

Pectoralis minor arises from ribs 3–5 and inserts on the coracoid process; it is a landmark for the three parts of the axillary artery (first part medial to, second part behind, third part lateral to the muscle) and protracts/depresses the scapula.

The pectoral nerves are named for the plexus cords they arise from, not the muscle they end in: the lateral pectoral nerve (C5–C7) comes off the lateral cord and supplies pectoralis major only; the medial pectoral nerve (C8–T1) comes off the medial cord, pierces and supplies pectoralis minor, then supplies the lower (sternocostal) pectoralis major.

Subclavius (nerve to subclavius, C5–C6) depresses and stabilises the clavicle and, by cushioning it, protects the underlying subclavian vessels and brachial plexus in a clavicular fracture.

Serratus anterior & scapular movements

Serratus anterior arises from the upper 8–9 ribs and inserts along the entire costal surface of the medial border of the scapula, with the bulk of its fibres converging on the inferior angle. This concentration at the inferior angle gives it powerful leverage for upward rotation.

Serratus anterior is supplied by the long thoracic nerve (C5–C7), which runs superficially on the muscle's outer surface and is vulnerable in axillary surgery and direct blows.

Injury to the long thoracic nerve paralyses serratus anterior and produces medial (winged) scapula: the medial border lifts off the chest wall, worst on wall-push or forward flexion, and overhead abduction beyond 90° is lost because the scapula cannot upwardly rotate.

Protraction (drawing the scapula forward around the chest wall, as in a punch) is performed chiefly by serratus anterior, assisted by pectoralis minor. Serratus anterior is nicknamed the "boxer's muscle".

Upward rotation of the scapula (turning the glenoid to face upward, essential for full overhead elevation) is produced by a force couple: serratus anterior (lower fibres pulling the inferior angle laterally/forward) plus the upper and lower fibres of trapezius. Loss of either component blocks elevation beyond ~90°.

Trapezius

Part	Origin	Insertion	Nerve	Action
Upper trapezius	External occipital protuberance, ligamentum nuchae	Lateral third of clavicle	Spinal accessory nerve (CN XI); proprioception C3–C4	Elevates scapula; upward rotation
Middle trapezius	Spinous processes C7–T3	Acromion, spine of scapula	Spinal accessory nerve (CN XI)	Retracts scapula
Lower trapezius	Spinous processes T4–T12	Medial end of spine of scapula	Spinal accessory nerve (CN XI)	Depresses scapula; upward rotation

Trapezius arises from a long midline field: the external occipital protuberance, medial third of the superior nuchal line, ligamentum nuchae, and the spinous processes of C7 through T12.

It inserts on the lateral third of the clavicle, the acromion, and the spine of the scapula — a continuous crescent that lets the three functional parts pull in different directions.

Motor supply is the spinal accessory nerve (cranial nerve XI), with sensory/proprioceptive fibres from the ventral rami of C3–C4. Because CN XI runs superficially across the posterior triangle of the neck, it is at risk in lymph-node biopsy, producing trapezius palsy and lateral (drooping-shoulder) winging.

Acting as a whole, trapezius retracts the scapula; the upper and lower fibres form the upward-rotation force couple with serratus anterior; the upper fibres elevate and the lower fibres depress the scapula.

Levator scapulae, rhomboids, latissimus dorsi, teres major

Muscle	Origin	Insertion	Nerve (root)	Action
Levator scapulae	Transverse processes C1–C4	Superior angle & upper medial border of scapula	Dorsal scapular nerve (C5) + C3–C4	Elevates scapula; downward rotation
Rhomboid major	Spinous processes T2–T5	Medial border of scapula below spine	Dorsal scapular nerve (C4–C5)	Retracts & downward-rotates scapula
Rhomboid minor	Spinous processes C7–T1	Medial border at root of spine	Dorsal scapular nerve (C4–C5)	Retracts & downward-rotates scapula
Latissimus dorsi	Spinous processes T7–L5, thoracolumbar fascia, iliac crest, lower 3–4 ribs	Floor of intertubercular groove of humerus	Thoracodorsal nerve (C6–C8)	Extends, adducts, medially rotates arm
Teres major	Dorsal surface of inferior angle of scapula	Medial lip of intertubercular groove of humerus	Lower subscapular nerve (C5–C6)	Adducts & medially rotates arm

Levator scapulae elevates the superior angle of the scapula and, with the rhomboids, downwardly rotates the glenoid.

The rhomboids retract (adduct) the scapula and, being deep to trapezius, are tested by pushing the elbow backward against resistance while palpating the medial border; their nerve is the dorsal scapular nerve.

Latissimus dorsi ("lats") is the great extensor–adductor–medial rotator that inserts in the floor of the intertubercular groove; with pectoralis major and teres major it forms the trio that adducts the abducted arm.

Teres major arises from the dorsal inferior angle of the scapula, inserts on the medial lip of the intertubercular groove, and — unlike its neighbour teres minor — is not a rotator cuff muscle and is supplied by the lower subscapular nerve (C5–C6).

Deltoid

Deltoid arises from an anterior–middle–posterior triad mirroring trapezius's insertion: the lateral third of the clavicle (anterior fibres), the acromion (middle fibres) and the spine of the scapula (posterior fibres).

All three parts converge on the deltoid tuberosity of the lateral humeral shaft. The middle (multipennate) fibres are the prime abductors from ~15° to 90°; anterior fibres flex and medially rotate; posterior fibres extend and laterally rotate. Deltoid is supplied by the axillary nerve (C5–C6), tested over the "regimental badge" area.

Axilla and scapular spaces

The axilla is a pyramidal space with an apex (cervico-axillary canal), base (skin/fascia of armpit) and four walls: anterior = pectoralis major and minor + subclavius; posterior = subscapularis, teres major and latissimus dorsi; medial = serratus anterior over ribs 1–4; lateral = the intertubercular groove of the humerus (narrow bony wall).

The axilla contains five groups of axillary lymph nodes — pectoral (anterior), subscapular (posterior), humeral (lateral), central, and apical — draining ~75% of the breast, the upper limb and the chest wall, ultimately to the subclavian lymph trunk.

The posterior scapular region contains three intermuscular passages defined by teres minor (above), teres major (below), the long head of triceps and the humerus:

Space	Boundaries	Transmits
Triangular space	Teres minor above, teres major below, long head of triceps laterally	Circumflex scapular vessels
Quadrangular space	Teres minor above, teres major below, long head of triceps medially, surgical neck of humerus laterally	Axillary nerve + posterior circumflex humeral vessels
Triangular interval	Teres major above, long head of triceps medially, lateral head of triceps/humeral shaft laterally	Radial nerve + profunda brachii vessels

The triangular space (medial) transmits the circumflex scapular artery (a branch of the subscapular artery) to the infraspinous fossa.

The quadrangular space transmits the axillary nerve and posterior circumflex humeral artery; entrapment here (quadrilateral space syndrome) denervates deltoid and teres minor.

The triangular interval (below teres major) is the exit for the radial nerve and profunda brachii artery as they pass to the posterior arm.

The Edge

Two windings deform the rules: trapezius/deltoid share a clavicle–acromion–scapular spine line (one inserts where the other arises), and the bicipital groove hosts pec major (lateral lip), teres major (medial lip) and lat dorsi (floor).
Winging localises: medial winging (worse on forward push) = long thoracic/serratus anterior; lateral winging (worse on abduction, shoulder drops) = spinal accessory/trapezius.

Clinical relevance (Moore's): The long thoracic nerve to serratus anterior runs superficially on the chest wall and is vulnerable during axillary node clearance or mastectomy, its injury producing winging of the scapula and loss of arm elevation above the horizontal; the spinal accessory nerve crossing the posterior triangle is at risk in lymph-node biopsy, and its loss drops the shoulder through trapezius paralysis. [Moore, Clinically Oriented Anatomy]

3. Rotator cuff

High-yield summary

The rotator cuff is the four short scapulohumeral muscles — supraspinatus, infraspinatus, teres minor and subscapularis (SITS) — that fuse with the capsule and dynamically compress the humeral head into the shallow glenoid ("concavity compression"). Three insert on the greater tuberosity (from top: supraspinatus on the superior facet, infraspinatus on the middle facet, teres minor on the inferior facet) and subscapularis inserts on the lesser tuberosity. The gap between supraspinatus and subscapularis is the rotator interval, bridged by the coracohumeral and superior glenohumeral ligaments and floored by the biceps long head.

The four cuff muscles

Muscle	Origin	Insertion	Nerve (root)	Action
Supraspinatus	Supraspinous fossa of scapula	Superior facet of greater tuberosity	Suprascapular nerve (C5–C6)	Initiates abduction (0–15°); stabilises head
Infraspinatus	Infraspinous fossa of scapula	Middle facet of greater tuberosity	Suprascapular nerve (C5–C6)	Lateral (external) rotation of arm
Teres minor	Upper/middle lateral border of scapula	Inferior facet of greater tuberosity	Axillary nerve (C5–C6)	Lateral (external) rotation; weak adduction
Subscapularis	Subscapular fossa (costal surface of scapula)	Lesser tuberosity of humerus	Upper & lower subscapular nerves (C5–C6)	Medial (internal) rotation; anterior stabiliser

The cuff (SITS) converts the deltoid's superiorly directed pull into a rotation about a stable fulcrum. Note the odd one out for innervation: three of the four are supraspinatus/infraspinatus (suprascapular nerve) and subscapularis (subscapular nerves), but teres minor is supplied by the axillary nerve — a favourite discriminator.

Supraspinatus arises from the supraspinous fossa, passes beneath the acromion and coracoacromial arch, and inserts on the superior facet of the greater tuberosity. It initiates the first ~15° of abduction and is the tendon most often torn and impinged.

Abduction is a two-part act: supraspinatus initiates and stabilises the head for the first ~15°, then deltoid (middle fibres) takes over as the prime mover to 90°; scapular upward rotation (serratus anterior + trapezius) completes elevation to 180°.

Infraspinatus (infraspinous fossa → middle facet of the greater tuberosity, suprascapular nerve) is the principal external rotator of the shoulder in the neutral (arm-by-side) position.

Teres minor (lateral scapular border → inferior facet of the greater tuberosity) is an external rotator and, uniquely among the cuff, is supplied by the axillary nerve (C5–C6) — hence teres minor wasting accompanies deltoid wasting in axillary nerve/quadrilateral space lesions.

Subscapularis (subscapular fossa → lesser tuberosity, upper and lower subscapular nerves) is the only anterior cuff muscle and the chief internal rotator and anterior stabiliser; tested by the lift-off and belly-press tests.

The greater tuberosity has three facets read from superior to inferior — superior (supraspinatus), middle (infraspinatus), inferior (teres minor) — while the lesser tuberosity takes subscapularis. Memorise the top-to-bottom order (Supra → Infra → teres minor) because the near-neighbour distractor is always swapping the infraspinatus and teres-minor facets.

Rotator interval & stabilisers

The rotator interval is the triangular gap between the anterior border of supraspinatus and the superior border of subscapularis. Its roof is formed by the coracohumeral ligament and superior glenohumeral ligament, and the long head of biceps tendon runs through it to enter the intertubercular groove; interval laxity contributes to instability, and interval contracture to frozen shoulder.

Shoulder stability is layered into static restraints (bony glenoid, labrum, capsule, glenohumeral ligaments, negative intra-articular pressure) and dynamic restraints (the rotator cuff via concavity compression, the long head of biceps, and the scapular stabilisers that keep the glenoid platform aligned). The cuff is the key dynamic stabiliser across the mid-range of motion.

The Edge

One muscle, one nerve trap: three cuff muscles follow the suprascapular/subscapular rule but teres minor is axillary — pair its wasting with deltoid to localise an axillary nerve lesion.
The facets run top-down S-I-T on the greater tuberosity; subscapularis alone crosses to the lesser tuberosity, so an "internal rotator that inserts anteriorly" can only be subscapularis.

Clinical relevance (Moore's): The supraspinatus tendon passes beneath the coracoacromial arch and is the commonest site of rotator-cuff tear and subacromial impingement, felt as a painful arc between 60 and 120 degrees; a relatively avascular critical zone near its insertion predisposes to degenerative and calcific tendinopathy. [Moore, Clinically Oriented Anatomy]

4. Arm muscles

High-yield summary

The arm (brachium) has two osteofascial compartments. The anterior (flexor) compartment — biceps brachii, brachialis, coracobrachialis — is supplied by the musculocutaneous nerve and flexes the elbow (biceps also supinates). The posterior (extensor) compartment — triceps brachii (and the small anconeus, functionally an extensor) — is supplied by the radial nerve and extends the elbow. Brachialis is the workhorse elbow flexor; biceps is the strongest supinator; the coracobrachialis is pierced by its own nerve.

Anterior (flexor) compartment

Muscle	Origin	Insertion	Nerve (root)	Action
Biceps brachii — long head	Supraglenoid tubercle of scapula	Radial tuberosity + bicipital aponeurosis to deep forearm fascia	Musculocutaneous nerve (C5–C6)	Supinates forearm; flexes elbow; weak shoulder flexor
Biceps brachii — short head	Apex of coracoid process	Radial tuberosity (common tendon)	Musculocutaneous nerve (C5–C6)	Flexes elbow; supinates
Brachialis	Distal anterior humerus	Tuberosity & coronoid process of ulna	Musculocutaneous nerve (C5–C6) + radial nerve (small lateral part)	Prime flexor of elbow (all positions)
Coracobrachialis	Apex of coracoid process	Middle of medial humeral shaft	Musculocutaneous nerve (C5–C7)	Flexes and adducts arm

The three anterior-compartment muscles are all supplied by the musculocutaneous nerve, which pierces coracobrachialis, runs between biceps and brachialis, and continues as the lateral cutaneous nerve of the forearm.

The long head of biceps arises from the supraglenoid tubercle (and superior labrum), running intra-articularly over the humeral head and then through the intertubercular groove — an important stabiliser and a common source of anterior shoulder pain.

The short head of biceps arises from the apex of the coracoid process, shared with coracobrachialis (the "conjoint tendon"), and lies medial to the long head.

Biceps inserts principally on the radial tuberosity, with the bicipital aponeurosis (lacertus fibrosus) fanning medially into the deep fascia over the flexor-pronator mass — protecting the underlying brachial artery and median nerve in the cubital fossa. Because it inserts on the radius medial to the axis, biceps is the most powerful supinator, strongest with the elbow flexed to 90°.

Biceps brachii is supplied by the musculocutaneous nerve (C5–C6); a lost biceps jerk and weak supination/flexion with numb lateral forearm localise a musculocutaneous or C5–C6 lesion.

Brachialis (distal anterior humerus → ulnar tuberosity and coronoid process) is the prime elbow flexor in every forearm position because it inserts on the ulna and is unaffected by pronation/supination. It is mainly musculocutaneous but carries a small radial nerve twig to its lateral part.

Coracobrachialis (coracoid apex → middle of the medial humeral shaft) flexes and adducts the arm and is pierced by the musculocutaneous nerve — the anatomical marker for that nerve.

Posterior (extensor) compartment

Muscle	Origin	Insertion	Nerve (root)	Action
Triceps — long head	Infraglenoid tubercle of scapula	Olecranon of ulna (common tendon)	Radial nerve (C6–C8)	Extends elbow; extends/adducts arm
Triceps — lateral head	Posterior humerus above radial groove	Olecranon of ulna	Radial nerve (C6–C8)	Extends elbow
Triceps — medial head	Posterior humerus below radial groove	Olecranon of ulna	Radial nerve (C6–C8)	Extends elbow (workhorse)

Triceps brachii is the sole significant contents of the posterior arm compartment, the main extensor of the elbow, supplied by the radial nerve (C6–C8) and tested by the triceps jerk.

Its three heads differ in origin: the long head from the infraglenoid tubercle of the scapula (the only head crossing the shoulder), the lateral head above the radial (spiral) groove, and the medial (deep) head below the groove. The lateral and long heads overlie the medial head, whose fibres run to the olecranon in all positions.

The long head arises from the infraglenoid tubercle, forms the medial boundary of the quadrangular/triangular spaces, and assists shoulder extension and adduction as well as elbow extension.

All three heads converge on a common tendon inserting on the posterior superior surface of the olecranon of the ulna. Anconeus (from the lateral epicondyle to the olecranon and posterior ulna, radial nerve) continues this line and assists extension while stabilising the elbow in pronation.

The Edge

Compartment = nerve = action: anterior arm is musculocutaneous and flexes; posterior arm is radial and extends — an "elbow flexor with radial supply" can only be brachioradialis (a forearm muscle), never a true arm flexor.
Brachialis flexes in any grip while biceps supination power collapses in pronation — so a "pure flexor unaffected by forearm rotation" is brachialis, and the strongest supinator is biceps at 90° flexion.

Clinical relevance (Moore's): A distal biceps tendon rupture retracts the muscle belly proximally as a Popeye deformity and weakens supination more than elbow flexion; the biceps reflex tests the C5-C6 musculocutaneous supply, and an injured musculocutaneous nerve abolishes it along with sensation over the lateral forearm. [Moore, Clinically Oriented Anatomy]

5. Forearm — flexor-pronator group

High-yield summary

The anterior forearm holds the flexor-pronator muscles in three layers, mostly from the common flexor origin on the medial epicondyle and supplied by the median nerve — with two important exceptions supplied by the ulnar nerve (flexor carpi ulnaris and the medial half of flexor digitorum profundus). The anterior interosseous nerve (a median branch) drives the deep muscles flexor pollicis longus, the lateral half of flexor digitorum profundus, and pronator quadratus. Learn which muscle bends which joint: FDS flexes the proximal interphalangeal (PIP) joints, FDP flexes the distal interphalangeal (DIP) joints.

Superficial and intermediate layers

Muscle	Origin	Insertion	Nerve (root)	Action
Pronator teres	Humeral head: medial epicondyle (common flexor origin); ulnar head: coronoid process	Middle of lateral surface of radius	Median nerve (C6–C7)	Pronates forearm; weak elbow flexor
Flexor carpi radialis	Medial epicondyle (common flexor origin)	Bases of 2nd (± 3rd) metacarpal	Median nerve (C6–C7)	Flexes & abducts (radially deviates) wrist
Palmaris longus	Medial epicondyle (common flexor origin)	Flexor retinaculum & palmar aponeurosis	Median nerve (C7–C8)	Tenses palmar aponeurosis; weak wrist flexor (absent in ~15%)
Flexor carpi ulnaris	Humeral head: medial epicondyle; ulnar head: olecranon & posterior ulna	Pisiform → hamate & 5th metacarpal (via pisohamate/pisometacarpal ligaments)	Ulnar nerve (C7–C8)	Flexes & adducts (ulnar deviates) wrist
Flexor digitorum superficialis	Humero-ulnar head (medial epicondyle, coronoid) + radial head (oblique line of radius)	Sides of middle phalanges of digits 2–5	Median nerve (C7–T1)	Flexes PIP joints (and MCP, wrist)

Pronator teres has two heads — a larger humeral head from the medial epicondyle and a small ulnar head from the coronoid process; the median nerve passes between them, a potential compression point (pronator syndrome).

Its origin is therefore dual: the medial epicondyle (common flexor origin) and the coronoid process of the ulna.

Pronator teres inserts on the middle of the lateral (convex) surface of the radial shaft — the pronator "wrap" point — to rotate the radius over the ulna.

Flexor carpi radialis crosses the wrist in its own tunnel (a split of the flexor retinaculum) to insert on the base of the 2nd metacarpal (with a slip to the 3rd).

Acting with extensor carpi radialis longus/brevis it produces radial deviation (abduction), and with flexor carpi ulnaris it produces wrist flexion — the classic "when two muscles pull, the shared action wins" force-couple.

Palmaris longus is a slender, frequently absent (~15%) muscle from the medial epicondyle to the flexor retinaculum and palmar aponeurosis; it is a common tendon graft donor and its tendon lies superficial to (not within) the carpal tunnel.

Flexor carpi ulnaris is the most medial superficial flexor; its tendon inserts on the pisiform, and continues via the pisohamate and pisometacarpal ligaments to the hook of hamate and base of the 5th metacarpal.

Flexor carpi ulnaris is one of only two forearm flexors supplied by the ulnar nerve (C7–C8) — the other being the medial half of flexor digitorum profundus.

Flexor digitorum superficialis tendons split (the "chiasma of Camper") to insert on the sides of the middle phalanges of the four fingers, so FDS flexes the proximal interphalangeal (PIP) joints; it lies in an intermediate layer of its own.

Flexor digitorum superficialis is supplied by the median nerve (C7–T1); independent PIP flexion of one finger with the others held extended is the bedside FDS test.

Deep layer

Muscle	Origin	Insertion	Nerve (root)	Action
Flexor digitorum profundus	Proximal ¾ of anterior/medial ulna & interosseous membrane	Bases of distal phalanges of digits 2–5	Median (AIN) to digits 2–3 (C8–T1); ulnar nerve to digits 4–5	Flexes DIP joints (and MCP, wrist)
Flexor pollicis longus	Anterior surface of radius & interosseous membrane	Base of distal phalanx of thumb	Anterior interosseous nerve (median, C8–T1)	Flexes IP & MCP joints of thumb
Pronator quadratus	Distal anterior ulna	Distal anterior radius	Anterior interosseous nerve (median, C8–T1)	Prime pronator; holds radius & ulna together

The long digital flexors are FDS (PIP) and FDP (DIP): FDP lies deep and flexes the distal phalanges, and because it also crosses PIP, MCP and wrist joints it flexes them once the DIP is anchored. Their tendons are held to the phalanges by fibrous flexor sheaths and pulleys.

Flexor digitorum profundus inserts on the bases of the distal phalanges of digits 2–5 and is the only muscle able to flex the DIP joints.

FDP has a split nerve supply: the lateral half (index and middle fingers) is supplied by the anterior interosseous nerve (median), and the medial half (ring and little fingers) by the ulnar nerve — the anatomical basis of the ulnar claw sparing the index/middle DIPs.

Flexor pollicis longus arises from the anterior surface of the radius and adjacent interosseous membrane (occasionally an accessory head from the coronoid/medial epicondyle — Gantzer's muscle).

It inserts on the base of the distal phalanx of the thumb, flexing the thumb IP joint; it is supplied by the anterior interosseous nerve.

The anterior interosseous nerve (AIN) is a purely motor branch of the median nerve that supplies FPL, the lateral half of FDP and pronator quadratus. An AIN lesion produces a weak "OK-sign" pinch (loss of thumb IP and index DIP flexion) with no sensory loss — a key discriminator from a carpal-tunnel median lesion.

Pronator quadratus (distal ulna → distal radius, AIN) is the prime and deepest pronator and the initiator of pronation, also binding the distal radioulnar joint.

The ulnar (medial) side of the anterior forearm is functionally the ulnar nerve's territory: flexor carpi ulnaris and the medial half of FDP are the only two forearm flexors it supplies, while the ulnar nerve itself descends alongside the ulnar artery deep to FCU, giving no muscular branches in the arm.

The Edge

The two ulnar-supplied forearm flexors are FCU and the medial half of FDP — everything else anterior is median (with the deep three via the anterior interosseous nerve).
FDS bends the PIP, FDP bends the DIP: a laceration that abolishes DIP flexion of one finger implicates that finger's FDP slip specifically, whereas isolated PIP flexion loss implicates FDS.

Clinical relevance (Moore's): The common flexor origin at the medial epicondyle is the site of medial epicondylitis (golfer elbow); the median nerve passes between the two heads of pronator teres and the ulnar nerve between the two heads of flexor carpi ulnaris, each a recognised entrapment point that reproduces the respective nerve distribution. [Moore, Clinically Oriented Anatomy]

6. Forearm — extensor-supinator group

High-yield summary

The posterior forearm holds the extensor-supinator muscles, almost all from the common extensor origin on the lateral epicondyle and supplied by the radial nerve — either directly (the mobile wad: brachioradialis, extensor carpi radialis longus, and often extensor carpi radialis brevis) or via its deep terminal branch, the posterior interosseous nerve (PIN). The superficial extensors run wrist-crossing and finger-extending; the deep extensors (the outcropping "outcropper" muscles) move the thumb and index. All the extensor tendons pass beneath the extensor retinaculum in six dorsal (extensor) compartments.

Superficial extensors ("mobile wad" + digital extensors)

Muscle	Origin	Insertion	Nerve (root)	Action
Brachioradialis	Upper lateral supracondylar ridge of humerus	Lateral distal radius (styloid process base)	Radial nerve (C5–C6)	Flexes elbow (mid-prone); "beer-raiser"
Extensor carpi radialis longus	Lower lateral supracondylar ridge	Base of 2nd metacarpal (dorsal)	Radial nerve (C6–C7)	Extends & radially deviates wrist
Extensor carpi radialis brevis	Lateral epicondyle (common extensor origin)	Base of 3rd metacarpal (dorsal)	Posterior interosseous nerve (radial, C7–C8)	Extends & radially deviates wrist
Extensor digitorum	Lateral epicondyle (common extensor origin)	Extensor expansions of digits 2–5 (middle & distal phalanges)	Posterior interosseous nerve (C7–C8)	Extends fingers (MCP chiefly) & wrist
Extensor digiti minimi	Lateral epicondyle (common extensor origin)	Extensor expansion of little finger	Posterior interosseous nerve (C7–C8)	Extends little finger
Extensor carpi ulnaris	Lateral epicondyle + posterior ulna	Base of 5th metacarpal	Posterior interosseous nerve (C7–C8)	Extends & ulnar-deviates wrist
Anconeus	Lateral epicondyle of humerus	Olecranon & posterior ulna	Radial nerve (C7–C8)	Assists extension; stabilises elbow in pronation

Brachioradialis is the anomaly of the group: a posterior-compartment muscle (radial nerve) that flexes the elbow. It is most efficient in mid-pronation and forms the lateral border of the cubital fossa.

It arises from the upper lateral supracondylar ridge and inserts far distally on the lateral surface of the radius just above the styloid process — the longest lever of the elbow flexors.

Brachioradialis is supplied by the radial nerve (C5–C6) proper (before the division into superficial and deep branches), so it is weak in a high radial nerve palsy but spared in a posterior interosseous nerve lesion — a useful localising sign.

Extensor carpi radialis longus arises from the lower lateral supracondylar ridge and inserts on the base of the 2nd metacarpal; it too is supplied by the radial nerve proper.

Extensor carpi radialis brevis arises from the common extensor origin (lateral epicondyle) — its degenerative tendinosis at that origin is "tennis elbow" (lateral epicondylitis).

Extensor carpi radialis brevis is supplied by the posterior interosseous nerve (or the deep radial branch just before it becomes PIN) — distinguishing it from its longus partner, which is supplied by the radial nerve proper.

Extensor digitorum arises from the common extensor origin and fans into the extensor expansions of the four fingers, chiefly extending the MCP joints; its tendons are linked on the dorsum by intertendinous connections (juncturae tendinum).

Extensor carpi ulnaris inserts on the base of the 5th metacarpal; with extensor carpi radialis longus/brevis it extends the wrist, and with flexor carpi ulnaris it ulnar-deviates the wrist.

Anconeus is a small triangular muscle from the lateral epicondyle to the olecranon and posterior ulna; supplied by the radial nerve, it assists elbow extension and stabilises the joint during pronation/supination.

Deep extensors ("outcroppers") & supinator

Muscle	Origin	Insertion	Nerve (root)	Action
Supinator	Lateral epicondyle, radial collateral & annular ligaments, supinator crest of ulna	Proximal lateral radius (wraps around)	Posterior interosseous nerve (radial, C5–C6/C7)	Supinates forearm (unassisted by elbow position)
Abductor pollicis longus	Posterior radius, ulna & interosseous membrane	Base of 1st metacarpal	Posterior interosseous nerve (C7–C8)	Abducts & extends thumb (CMC)
Extensor pollicis brevis	Posterior radius & interosseous membrane	Base of proximal phalanx of thumb	Posterior interosseous nerve (C7–C8)	Extends thumb MCP
Extensor pollicis longus	Posterior ulna & interosseous membrane	Base of distal phalanx of thumb	Posterior interosseous nerve (C7–C8)	Extends thumb IP; uses Lister's tubercle as pulley
Extensor indicis	Posterior ulna & interosseous membrane	Extensor expansion of index finger	Posterior interosseous nerve (C7–C8)	Extends index (independent pointing)

Every deep extensor is supplied by the posterior interosseous nerve (PIN), the deep terminal (motor) branch of the radial nerve, which reaches them after passing through supinator.

Supinator has a dual origin: a superficial head from the lateral epicondyle, radial collateral ligament and annular ligament, and a deep head from the supinator crest and fossa of the ulna; it wraps around the proximal radius to supinate.

The posterior interosseous nerve passes between the two heads of supinator through the fibrous arcade of Frohse — the commonest site of PIN entrapment (radial tunnel/PIN syndrome).

Abductor pollicis longus inserts on the base of the 1st metacarpal, abducting and extending the thumb at the carpometacarpal joint; it forms the palmar (radial) border of the anatomical snuffbox.

Extensor pollicis brevis inserts on the base of the proximal phalanx of the thumb and lies just dorsal to abductor pollicis longus in the first dorsal compartment (both inflamed in de Quervain tenosynovitis).

Extensor pollicis longus inserts on the base of the distal phalanx of the thumb, hooking around Lister's (dorsal) tubercle of the radius as a pulley to change its line of pull and form the ulnar (dorsal) border of the snuffbox.

Extensor indicis inserts into the extensor expansion of the index finger (on the ulnar side of the extensor digitorum tendon), allowing independent index extension (pointing).

Dorsal (extensor) compartments

Six compartments pass deep to the extensor retinaculum, read radial to ulnar (mnemonic "2, 2, 1, 2, 1, 1 tendons"):

#	Tendons	Note
1	Abductor pollicis longus, extensor pollicis brevis	de Quervain tenosynovitis
2	Extensor carpi radialis longus & brevis	Radial wrist extensors
3	Extensor pollicis longus	Turns at Lister's tubercle
4	Extensor digitorum, extensor indicis	+ posterior interosseous nerve on floor
5	Extensor digiti minimi	Over distal radioulnar joint
6	Extensor carpi ulnaris	In groove on dorsal ulnar head

The first dorsal compartment contains abductor pollicis longus and extensor pollicis brevis; their shared tenosynovitis is de Quervain disease, positive on Finkelstein's test.

The third dorsal compartment contains extensor pollicis longus, which angles sharply around Lister's tubercle — the site where the tendon can rupture after a distal radius (Colles') fracture.

The fifth dorsal compartment contains extensor digiti minimi, sitting over the distal radioulnar joint; it is the reliable landmark for that joint on the dorsum of the wrist.

The Edge

The radial-nerve-proper muscles are brachioradialis and extensor carpi radialis longus; everything else posterior is posterior interosseous nerve — so PIN palsy gives finger drop with preserved wrist extension (radial-deviated, via spared ECRL) and no sensory loss.
Snuffbox borders decode the deep extensors: abductor pollicis longus + extensor pollicis brevis form the radial wall, extensor pollicis longus the ulnar wall — three of the deep "outcroppers" bound one clinical landmark.

Clinical relevance (Moore's): The common extensor origin at the lateral epicondyle is the site of lateral epicondylitis (tennis elbow); the posterior interosseous nerve winds through supinator and can be compressed there, giving finger-drop with preserved wrist extension and no sensory loss. [Moore, Clinically Oriented Anatomy]

7. Intrinsic muscles of the hand

High-yield summary

The intrinsic hand muscles are grouped into the thenar (median-supplied, moving the thumb), hypothenar (ulnar-supplied, moving the little finger), the adductor pollicis, and the lumbricals and interossei that work the extensor expansion. The single most tested rule: the ulnar nerve supplies all intrinsic hand muscles except LOAF — the Lateral two lumbricals, Opponens pollicis, Abductor pollicis brevis and Flexor pollicis brevis (median). The interossei and lumbricals flex the MCP and extend the interphalangeal joints, the basis of both the "Z" clawing patterns.

Thenar eminence

Muscle	Origin	Insertion	Nerve (root)	Action
Abductor pollicis brevis	Flexor retinaculum, scaphoid & trapezium tubercles	Radial base of proximal phalanx of thumb	Recurrent branch of median nerve (C8–T1)	Abducts thumb (palmar)
Flexor pollicis brevis	Flexor retinaculum & trapezium (superficial head); trapezoid/capitate (deep head)	Radial base of proximal phalanx of thumb (over radial sesamoid)	Superficial head: recurrent median; deep head: deep ulnar (C8–T1)	Flexes thumb MCP
Opponens pollicis	Flexor retinaculum & tubercle of trapezium	Whole radial (lateral) border of 1st metacarpal	Recurrent branch of median nerve (C8–T1)	Opposes thumb (flexion + medial rotation)
Adductor pollicis	Transverse head: 3rd metacarpal shaft; oblique head: capitate & bases of 2nd–3rd metacarpals	Ulnar base of proximal phalanx of thumb (over ulnar sesamoid)	Deep branch of ulnar nerve (C8–T1)	Adducts thumb

The three true thenar muscles — abductor pollicis brevis, flexor pollicis brevis (superficial head) and opponens pollicis — are supplied by the recurrent (motor) branch of the median nerve, so a low median nerve lesion produces thenar wasting and loss of thumb opposition ("ape hand").

Abductor pollicis brevis (flexor retinaculum/scaphoid-trapezium tubercles → radial base of the thumb's proximal phalanx) is the purest test of the recurrent median nerve — palmar abduction against resistance.

Flexor pollicis brevis has two heads with a split nerve supply: the superficial head from the recurrent median nerve and the deep head from the deep ulnar nerve — a classic exception straddling the LOAF rule.

Opponens pollicis is the deepest thenar muscle and the only one inserting along the whole radial shaft of the 1st metacarpal (not the phalanx); it rotates and flexes the metacarpal to bring the thumb pad to face the fingers.

Adductor pollicis has a transverse head (from the anterior shaft of the 3rd metacarpal) and an oblique head (from the capitate and bases of the 2nd–3rd metacarpals), converging on the ulnar base of the thumb's proximal phalanx.

Adductor pollicis is supplied by the deep branch of the ulnar nerve; its weakness underlies Froment's sign (thumb IP flexion by flexor pollicis longus substituting for a weak adductor when pinching paper).

Hypothenar eminence

Muscle	Origin	Insertion	Nerve (root)	Action
Abductor digiti minimi	Pisiform & pisohamate ligament	Ulnar base of proximal phalanx of little finger	Deep branch of ulnar nerve (C8–T1)	Abducts little finger
Flexor digiti minimi brevis	Hook of hamate & flexor retinaculum	Ulnar base of proximal phalanx of little finger	Deep branch of ulnar nerve (C8–T1)	Flexes little finger MCP
Opponens digiti minimi	Hook of hamate & flexor retinaculum	Ulnar (medial) border of 5th metacarpal	Deep branch of ulnar nerve (C8–T1)	Opposes/cups the little finger
Palmaris brevis	Flexor retinaculum & palmar aponeurosis	Skin of medial (ulnar) palm	Superficial branch of ulnar nerve (C8–T1)	Wrinkles skin, deepens hypothenar hollow

The hypothenar muscles mirror the thenar three (abductor, flexor, opponens) but are all supplied by the deep branch of the ulnar nerve; their wasting deepens the interosseous furrows in ulnar palsy.

Abductor digiti minimi (pisiform → ulnar base of the little finger's proximal phalanx) is the most medial and superficial hypothenar muscle and the standard clinical test of the deep ulnar branch.

Flexor digiti minimi brevis (hook of hamate/flexor retinaculum → ulnar base of the little finger's proximal phalanx) flexes the little finger MCP joint alongside abductor digiti minimi.

Opponens digiti minimi is the deep hypothenar muscle inserting on the medial border of the 5th metacarpal, rotating it to cup the palm in opposition.

Palmaris brevis is a small dermal muscle in the superficial fascia of the hypothenar eminence, uniquely supplied by the superficial (not deep) branch of the ulnar nerve; it corrugates the ulnar palmar skin to improve grip.

Lumbricals & interossei

Muscle	Origin	Insertion	Nerve (root)	Action
Lumbricals 1 & 2 (radial two)	Radial side of FDP tendons to index & middle	Radial side of extensor expansions (index, middle)	Median nerve (C8–T1)	Flex MCP, extend PIP/DIP
Lumbricals 3 & 4 (ulnar two)	Adjacent (bipennate) FDP tendons to ring/little	Radial side of extensor expansions (ring, little)	Deep branch of ulnar nerve (C8–T1)	Flex MCP, extend PIP/DIP
Palmar interossei (3–4)	Palmar surfaces of metacarpals 2, 4, 5 (single-headed)	Extensor expansions/proximal phalanx bases of same digits	Deep branch of ulnar nerve (C8–T1)	ADduct fingers to midline (PAD)
Dorsal interossei (4)	Adjacent sides of two metacarpals (bipennate)	Extensor expansions/proximal phalanx bases	Deep branch of ulnar nerve (C8–T1)	ABduct fingers from midline (DAB)

The four lumbricals are unique in arising from tendon (FDP) rather than bone and inserting into the extensor expansions, linking the deep flexor to the extensor mechanism.

They originate from the radial sides of the flexor digitorum profundus tendons: the radial two (1st and 2nd) are unipennate from single tendons, and the ulnar two (3rd and 4th) are bipennate from adjacent tendon pairs.

Their nerve supply follows the FDP rule: the radial two lumbricals are median (part of LOAF), the ulnar two are deep ulnar — split innervation matching the flexor tendons they arise from.

Because they pass palmar to the MCP axis but dorsal to the interphalangeal (IP) axes, the lumbricals and interossei flex the MCP joints and simultaneously extend the PIP and DIP joints — the "intrinsic-plus" position; their failure produces the clawed "intrinsic-minus" hand.

The interossei are all supplied by the deep branch of the ulnar nerve and, like the lumbricals, flex the MCP while extending the IP joints in addition to their abduction/adduction roles.

Palmar interossei ADduct the fingers toward the middle-finger axis (PAD); they are unipennate, arising from the metacarpal of the digit they move (2, 4, 5).

Dorsal interossei ABduct the fingers away from the axis (DAB); they are bipennate, arising from the adjacent sides of two metacarpals, and are the muscles wasted first and most visibly (first web space) in ulnar palsy.

Palmar fascia & extensor expansion

The palmar aponeurosis is the thickened central part of the deep palmar fascia, continuous proximally with palmaris longus and the flexor retinaculum, splitting distally into four digital slips; its pathological contracture is Dupuytren disease (ring and little fingers).

The extensor (dorsal) expansion is a triangular fibrous hood over the dorsum of each finger into which extensor digitorum, the lumbricals and interossei insert; the central slip reaches the middle phalanx and the two lateral bands reach the distal phalanx, coordinating MCP extension with IP extension.

The Edge

LOAF is the whole game: if a thumb/hand intrinsic is not one of the lateral two lumbricals, opponens pollicis, abductor pollicis brevis or flexor pollicis brevis, it is ulnar — so an ulnar claw spares the index/middle (median lumbricals) but claws the ring/little.
PAD/DAB plus the lumbrical geometry (palmar to MCP, dorsal to IP) explains the claw: lose the ulnar intrinsics and the MCPs hyperextend while the IPs flex in the ring and little fingers.

Clinical relevance (Moore's): A low ulnar nerve lesion paralyses most intrinsics and produces clawing of the ring and little fingers (an ulnar claw made worse because the long flexors are spared), whereas thenar wasting with loss of thumb opposition points instead to a median nerve lesion at the carpal tunnel. [Moore, Clinically Oriented Anatomy]

8. Brachial plexus & peripheral nerves

High-yield summary

The brachial plexus is built from the ventral rami of C5–T1 and organised as Roots → Trunks → Divisions → Cords → Branches ("Read That Damn Cadaver Book"). Three trunks (upper C5–C6, middle C7, lower C8–T1) each split into anterior and posterior divisions; the divisions regroup into three cords (lateral, medial, posterior) named for their relation to the axillary artery; and the cords give the five terminal nerves — musculocutaneous, axillary, radial, median and ulnar. Master the root values and the "who supplies what" so that a lesion (Erb's, Klumpke's, wrist drop, claw hand) can be localised precisely.

Plexus architecture

The plexus arises from the ventral (anterior) rami of C5, C6, C7, C8 and T1. Pre-fixed (C4 contribution) and post-fixed (T2 contribution) variants occur. Roots emerge between scalenus anterior and medius.

The roots form three trunks: the upper trunk (C5–C6), middle trunk (C7) and lower trunk (C8–T1). The upper trunk gives two branches directly — the suprascapular nerve and the nerve to subclavius — and its point on the posterior triangle is Erb's point.

Each trunk splits into anterior and posterior divisions behind the clavicle; these recombine into three cords named for their position relative to the second part of the axillary artery.

The lateral cord (anterior divisions of upper + middle trunks; C5–C7) gives the musculocutaneous nerve, the lateral pectoral nerve, and the lateral root of the median nerve.

The medial cord (anterior division of the lower trunk; C8–T1) gives the ulnar nerve, the medial root of the median nerve, the medial pectoral nerve, and the medial cutaneous nerves of the arm and forearm.

The posterior cord (posterior divisions of all three trunks; C5–T1) gives the radial and axillary nerves plus the upper subscapular, thoracodorsal and lower subscapular nerves ("ULTRA": Upper subscapular, Lower subscapular, Thoracodorsal, Radial, Axillary).

Terminal nerves — courses and roots

Nerve	Roots	Origin	Motor supply (summary)
Musculocutaneous	C5–C7 (mainly C5–C6)	Lateral cord	Coracobrachialis, biceps, brachialis; skin of lateral forearm
Axillary	C5–C6	Posterior cord	Deltoid, teres minor; skin over deltoid
Radial	C5–T1	Posterior cord	Triceps, anconeus, brachioradialis, extensors (via PIN)
Median	C6–T1 (± C5)	Lateral + medial roots	Most forearm flexors, thenar (LOAF), lateral 2 lumbricals
Ulnar	C8–T1 (± C7)	Medial cord	FCU, medial FDP, most hand intrinsics

The musculocutaneous nerve pierces coracobrachialis, runs between biceps and brachialis supplying all three anterior arm muscles, and emerges lateral to the biceps tendon as the lateral cutaneous nerve of the forearm.

It arises from the lateral cord (C5–C7); an isolated lesion gives weak elbow flexion/supination, a lost biceps jerk and lateral forearm numbness.

The axillary nerve arises from the posterior cord (C5–C6).

It passes through the quadrangular space with the posterior circumflex humeral artery and wraps around the surgical neck of the humerus, supplying deltoid and teres minor and the skin over the lower deltoid (upper lateral cutaneous nerve of the arm). It is injured in surgical-neck fractures and anterior shoulder dislocation — test sensation over the "regimental badge" before and after reduction.

The ulnar nerve (medial cord, C8–T1) passes down the medial arm, gives no branches in the arm, pierces the medial intermuscular septum at mid-arm to enter the posterior compartment, and passes behind the medial epicondyle (the cubital tunnel) before entering the forearm between the two heads of flexor carpi ulnaris.

In the arm the median nerve runs with the brachial artery, lying lateral to it proximally and crossing to lie medial to the artery at the elbow (usually anterior to the artery). It gives no muscular branches in the arm and enters the cubital fossa medial to the artery and biceps tendon.

The suprascapular nerve (C5–C6) branches from the upper trunk, passes through the suprascapular notch beneath the superior transverse scapular ligament ("Army over the bridge, Navy under" — the artery passes over the ligament, the nerve under) to supply supraspinatus, then around the spinoglenoid notch to supply infraspinatus. Entrapment (or a spinoglenoid cyst) causes selective infraspinatus wasting.

The dorsal scapular nerve (C5) arises directly from the C5 root, pierces scalenus medius, and supplies the rhomboids and levator scapulae; its injury causes lateral scapular drift.

The recurrent (motor) branch of the median nerve is given off just distal to the flexor retinaculum and loops back into the thenar eminence to supply abductor pollicis brevis, opponens pollicis and the superficial head of flexor pollicis brevis; its superficial course makes it vulnerable to lacerations of the "no-man's-land" of the thenar palm.

The deep branch of the ulnar nerve is a purely motor branch that dives between the hypothenar muscles and hooks across the palm with the deep palmar arch, supplying the hypothenar muscles, all interossei, the medial two lumbricals, adductor pollicis and the deep head of flexor pollicis brevis.

The posterior interosseous nerve (PIN) is the deep terminal branch of the radial nerve; after supplying extensor carpi radialis brevis and supinator, it passes through the supinator (arcade of Frohse) to supply the remaining extensors.

A PIN lesion produces finger drop, not wrist drop: the wrist still extends (extensor carpi radialis longus is supplied by the radial nerve proper, above the PIN) but deviates radially because extensor carpi ulnaris is lost, and there is no sensory loss (PIN is purely motor). This distinguishes a PIN palsy from a high radial-nerve palsy in the spiral groove.

The anterior interosseous nerve (AIN) is the equivalent deep motor branch on the flexor side — a purely motor branch of the median nerve supplying flexor pollicis longus, the lateral half of flexor digitorum profundus and pronator quadratus; its lesion gives a weak pinch (loss of the "OK" sign) with no sensory deficit.

Sensory territories

Hand dermatomes: the thumb/radial side is C6, the middle finger is C7, and the little finger/ulnar side is C8 — distinct from peripheral-nerve territories, which cross dermatome boundaries.

Autonomous (signature) zones are the small skin areas supplied by a single peripheral nerve with no overlap: the median nerve = pulp of the index finger, the ulnar nerve = pulp of the little finger, and the radial nerve = dorsal first web space (skin over the base of the thumb/1st dorsal interosseous). These are the reliable sites to test each nerve's sensation.

Nerve lesions & deformities

Erb–Duchenne palsy is an upper trunk (C5–C6) injury (excess head–shoulder separation: birth traction, motorbike fall). The arm hangs adducted, internally rotated and pronated with the forearm extended — the "waiter's tip" posture — from loss of the deltoid, cuff, biceps, brachialis and supinator.

Klumpke palsy is a lower trunk (C8–T1) injury (forced arm abduction, e.g. grabbing to break a fall). It paralyses the intrinsic hand muscles, producing a claw hand, and if the T1 sympathetic fibres are involved may cause Horner syndrome (ptosis, miosis, anhidrosis).

Wrist drop is the hallmark of a radial nerve lesion in the arm (spiral groove): loss of the wrist and finger extensors leaves the wrist flexed and unable to extend, with sensory loss over the dorsal first web space; triceps is spared if the lesion is distal to its branches.

Ape hand results from a median nerve lesion with thenar wasting: the thumb cannot oppose or abduct and falls back into the plane of the palm (adductus), so the flat, monkey-like hand is unable to grip a bottle (positive bottle sign).

The ulnar claw (hyperextended MCP, flexed IP of the ring and little fingers) follows a low ulnar nerve lesion at the wrist: loss of the medial two lumbricals and interossei unbalances the long flexors/extensors. Paradoxically the deformity is worse in low (distal) lesions because a high lesion also weakens the ulnar half of FDP ("ulnar paradox").

The Edge

Localise by combining motor and sensory: wrist drop + dorsal web-space numbness = radial; claw + ulnar-1½-finger numbness = ulnar; ape hand + index-pulp numbness = median.
Two "no branches in the arm" nerves — median and ulnar — travel with the brachial artery; only the ulnar leaves it to pass behind the medial epicondyle, which is why elbow trauma classically hits the ulnar nerve.

Clinical relevance (Moore's): Upper-trunk (C5-C6) traction gives Erb palsy with the waiter-tip posture of an adducted, medially rotated, extended and pronated limb, while lower-trunk (C8-T1) traction gives Klumpke palsy with intrinsic-hand paralysis and, if the T1 sympathetic fibres are avulsed, an associated Horner syndrome. [Moore, Clinically Oriented Anatomy]

9. Arterial supply & regional spaces

High-yield summary

The limb's arterial axis is a single named vessel that changes name as it descends: subclavian → axillary → brachial → (radial + ulnar) → palmar arches. The axillary artery is divided into three parts by pectoralis minor; the brachial artery runs down the anterior arm with the median nerve and bifurcates in the cubital fossa; and the radial and ulnar arteries reunite in the hand as the superficial and deep palmar arches. Know the branches at each level and the contents/boundaries of the cubital fossa.

Axillary artery

The axillary artery is the continuation of the subclavian artery beyond the lateral border of the first rib, ending at the inferior border of teres major, where it becomes the brachial artery. Pectoralis minor crosses it and divides it into three parts (first part medial to the muscle, second behind, third lateral).

Its branches number "1, 2, 3" by part (mnemonic: Save The London Scottish And Pakistan): part 1 — superior thoracic; part 2 — thoraco-acromial and lateral thoracic; part 3 — subscapular (largest; gives circumflex scapular + thoracodorsal) and the anterior and posterior circumflex humeral arteries (the posterior accompanies the axillary nerve through the quadrangular space).

Brachial artery

The brachial artery runs down the anterior arm on brachialis and the medial side, with the median nerve crossing it from lateral to medial. Its main branches are the profunda brachii (deep brachial) artery (which accompanies the radial nerve in the spiral groove) and the superior and inferior ulnar collateral arteries feeding the elbow anastomosis. It ends in the cubital fossa opposite the neck of the radius by dividing into the radial and ulnar arteries.

Cubital fossa

The cubital fossa is the triangular hollow in front of the elbow. Its contents from lateral to medial are the biceps Tendon, brachial Artery, median Nerve (mnemonic "TAN"), plus the radial nerve deep under brachioradialis; the roof carries the median cubital vein and bicipital aponeurosis, the floor is brachialis and supinator.

Its boundaries are: laterally the medial border of brachioradialis; medially the lateral border of pronator teres; the superior base an imaginary line between the two epicondyles; the apex points distally where brachioradialis overlaps pronator teres.

Forearm and hand arteries

The radial artery winds dorsally around the wrist, crossing the floor of the anatomical snuffbox (over the scaphoid and trapezium) before diving between the two heads of the first dorsal interosseous to form the deep palmar arch. Its pulse is palpable proximal to the snuffbox at the distal radius.

The hand is supplied by two anastomotic arches: the superficial palmar arch is the direct continuation of the ulnar artery (completed by the superficial branch of the radial artery), lying distal, and gives the common palmar digital arteries; the deep palmar arch is the continuation of the radial artery (completed by the deep branch of the ulnar artery), lying more proximal. Patency of both underlies Allen's test.

The Edge

One axis, four names: a stab anywhere along subclavian → axillary → brachial → radial/ulnar bleeds from the "same" vessel, and the collateral anastomoses around the scapula and elbow keep the limb alive when the main trunk is ligated between them.
The superficial arch is mostly ulnar and the deep arch mostly radial — mirror of the two wrist pulses — so a lacerated superficial arch bleeds from the ulnar side of the hand.

Clinical relevance (Moore's): The brachial artery lies medial to the biceps tendon in the cubital fossa and is the site for blood-pressure auscultation and brachial pulse; because the forearm arteries anastomose richly around the elbow and wrist, the radial artery can be harvested or cannulated provided an Allen test confirms an intact ulnar and palmar-arch supply. [Moore, Clinically Oriented Anatomy]

10. Joints & ligaments

High-yield summary

The upper limb links to the trunk through the sternoclavicular (SC) and acromioclavicular (AC) joints and moves at the highly mobile glenohumeral (GH) joint, the hinge/pivot elbow, and the ellipsoid wrist (radiocarpal) joint. Each has a signature joint type and a set of stabilising ligaments; the GH joint trades stability for range and depends on the labrum, glenohumeral ligaments and cuff, while the SC joint's chief stabiliser is the costoclavicular ligament and the AC joint's vertical stability comes from the coracoclavicular ligaments.

Glenohumeral joint

The glenohumeral joint is a synovial ball-and-socket (spheroidal) joint — the most mobile and least stable joint in the body, the shallow glenoid holding only ~⅓ of the humeral head, deepened ~50% by the fibrocartilaginous glenoid labrum.

The capsule is reinforced by the superior, middle and inferior glenohumeral ligaments (thickenings on the anterior capsule) plus the coracohumeral ligament. The inferior glenohumeral ligament is the key restraint to anterior dislocation with the arm abducted and externally rotated, and its avulsion produces the Bankart lesion.

Stability is static (bony glenoid version, labrum, capsuloligamentous complex, negative intra-articular pressure) plus dynamic (rotator cuff concavity compression, biceps long head, scapular stabilisers). The anteroinferior labrum and inferior glenohumeral ligament are the most important static anterior restraints in abduction/external rotation.

Acromioclavicular & sternoclavicular joints

The acromioclavicular (AC) joint is a plane synovial joint with a fibrocartilaginous articular disc, between the lateral clavicle and the acromion.

Its own acromioclavicular ligament provides horizontal (anteroposterior) stability, while vertical stability is provided by the strong coracoclavicular ligaments — the conoid (medial) and trapezoid (lateral) — running from coracoid to clavicle; their rupture allows the clavicle to ride up (AC joint separation, "step deformity").

The sternoclavicular (SC) joint is a saddle-type synovial joint with a complete fibrocartilaginous disc; it is the only bony articulation between the upper limb and the axial skeleton.

Despite its shallow bony fit it rarely dislocates because of strong ligaments: the anterior and posterior sternoclavicular ligaments, the interclavicular ligament, and — the principal stabiliser — the costoclavicular ligament anchoring the clavicle to the first rib.

Elbow joint

The elbow is a synovial joint with three articulations in one capsule: the humero-ulnar (trochlea–trochlear notch, a hinge), the humero-radial (capitulum–radial head), and the proximal radio-ulnar (radial head–radial notch, a pivot). Flexion/extension occur at the first two; pronation/supination at the third.

The medial ulnar collateral ligament (UCL) is a triangular complex; its anterior band is the primary restraint to valgus stress (injured in throwers — "Tommy John" reconstruction) running from the medial epicondyle to the coronoid/sublime tubercle.

Laterally, the radial collateral ligament runs from the lateral epicondyle to blend with the annular ligament, which encircles the radial head and holds it against the radial notch of the ulna, permitting rotation; in children the head can slip out of the annular ligament ("pulled elbow"/nursemaid's elbow).

Wrist joint

The wrist (radiocarpal) joint is an ellipsoid (condyloid) synovial joint between the distal radius and its articular disc proximally and the proximal carpal row (scaphoid, lunate, triquetrum) distally, allowing flexion/extension and radial/ulnar deviation; the ulna does not directly articulate (separated by the triangular fibrocartilage complex).

The Edge

Match the joint to its stabiliser: SC = costoclavicular ligament, AC (vertical) = coracoclavicular (conoid + trapezoid), GH (anterior, abducted/ER) = inferior glenohumeral ligament + anteroinferior labrum.
The annular ligament, not a collateral, holds the radial head — so a toddler's "pulled elbow" from axial traction is radial-head subluxation out of the annular ring, reduced by supination/flexion.

Clinical relevance (Moore's): The glenohumeral joint is least supported inferiorly, so dislocation is typically anteroinferior and risks the axillary nerve and a Bankart or Hill-Sachs lesion; acromioclavicular separation follows disruption of the coracoclavicular (conoid and trapezoid) ligaments. [Moore, Clinically Oriented Anatomy]

11. Carpal bones, carpal tunnel, snuffbox & compartments

High-yield summary

The eight carpal bones sit in two rows — proximal (scaphoid, lunate, triquetrum, pisiform) and distal (trapezium, trapezoid, capitate, hamate). The flexor retinaculum roofs the concave carpus to form the carpal tunnel, transmitting the median nerve and nine flexor tendons. Ulnar-sided structures pass superficial to the retinaculum through Guyon's canal. The anatomical snuffbox, floored by the scaphoid, is the clinical window to scaphoid fractures and the radial artery.

Carpal bones

The proximal carpal row (radial → ulnar) is Scaphoid, Lunate, Triquetrum, Pisiform; the distal row is Trapezium, Trapezoid, Capitate, Hamate (mnemonic "Some Lovers Try Positions That They Can't Handle"). The pisiform is a sesamoid in the flexor carpi ulnaris tendon and does not participate in the radiocarpal joint.

The trapezium is the most radial bone of the distal row; it carries a tubercle and a groove for flexor carpi radialis, and its saddle-shaped facet forms the first carpometacarpal (thumb) joint with the base of the 1st metacarpal — the joint that gives the thumb its opposition (and a common site of osteoarthritis).

Flexor retinaculum & carpal tunnel

The flexor retinaculum (transverse carpal ligament) is a strong fibrous band forming the roof of the carpal tunnel. It attaches radially to the tubercle of the scaphoid and the tubercle of the trapezium and ulnarly to the pisiform and the hook of the hamate, converting the anterior carpal groove into an osteofascial tunnel.

The carpal tunnel is bounded by the concave carpal bones (floor and sides) and the flexor retinaculum (roof). Raised pressure within it compresses the median nerve — carpal tunnel syndrome — the commonest entrapment neuropathy.

The tunnel transmits ten structures: the median nerve plus nine flexor tendons — the four flexor digitorum superficialis, the four flexor digitorum profundus, and the single flexor pollicis longus. Palmaris longus and the ulnar nerve/artery pass superficial to (outside) the retinaculum, which is why thenar sensation over the palm (via the palmar cutaneous branch, given off proximal to the tunnel) is spared in carpal tunnel syndrome.

Guyon's canal

Guyon's canal (the ulnar tunnel) is the passage for the ulnar nerve and ulnar artery at the wrist, lying superficial to the flexor retinaculum. Its floor is the flexor retinaculum and pisohamate ligament; its roof is the palmar carpal ligament and palmaris brevis.

Its walls are the pisiform (medial) and the hook of the hamate (lateral); within it the ulnar nerve divides into superficial (sensory) and deep (motor) branches, so compression here (handlebar palsy, ganglion) can be purely motor, purely sensory or mixed — sparing the dorsal ulnar skin (whose branch leaves proximally).

Anatomical snuffbox

The anatomical snuffbox is bounded radially by the tendons of abductor pollicis longus and extensor pollicis brevis and ulnarly by extensor pollicis longus; its floor is the scaphoid and trapezium, and crossing that floor is the radial artery. The superficial radial nerve runs over its roof.

Because the scaphoid forms the floor, tenderness in the anatomical snuffbox after a fall on the outstretched hand signals a scaphoid fracture. The scaphoid's blood supply enters distally and runs retrograde, so a proximal-pole fracture risks avascular necrosis and non-union — hence a clinically suspected fracture is immobilised even when initial radiographs look normal.

The Edge

Nine tendons + one nerve = ten in the carpal tunnel; palmaris longus and the ulnar nerve/artery are outside it, and the median palmar cutaneous branch is given off proximal to it — which is why the central palm keeps its sensation in carpal tunnel syndrome.
Snuffbox tenderness = scaphoid until proven otherwise: a normal first X-ray does not exclude it, and the retrograde blood supply makes the proximal pole the danger zone for avascular necrosis.

Clinical relevance (Moore's): The scaphoid, palpable in the anatomical snuffbox, has a retrograde blood supply so a waist fracture risks avascular necrosis of the proximal pole and non-union; carpal tunnel syndrome compresses the median nerve deep to the flexor retinaculum but spares the palmar cutaneous branch, which passes superficial to it. [Moore, Clinically Oriented Anatomy]

Sources cited in this document

Last's Anatomy: Regional and Applied (McMinn RMH, ed.) — regional upper limb anatomy, muscle attachments, nerve courses and joints.
Gray's Anatomy for Students / Gray's Anatomy — osteology, brachial plexus organisation, arterial branches and clinical correlations.
Osmosis — muscle origin/insertion/innervation/action summaries and peripheral nerve lesion patterns.

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