Anatomy
MBBS Anatomy question bank: general anatomy and osteology, regional gross anatomy (upper limb, lower limb, thorax, abdomen, pelvis, head and neck), neuroanatomy, histology and embryology.
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Definition
The axilla is a pyramidal space between the arm and chest wall that transmits vessels and nerves; the brachial plexus (C5–T1) supplies the upper limb.
Boundaries of the Axilla
- Apex — cervico-axillary canal
- Base — skin of the armpit
- Anterior wall — pectoralis major & minor
- Posterior wall — subscapularis, teres major, latissimus dorsi
- Medial — serratus anterior; Lateral — bicipital groove
Contents
- Axillary artery and vein
- Cords of the brachial plexus
- Axillary lymph nodes
- Axillary fat
Brachial Plexus (roots → branches)
- Roots C5–T1 → trunks → divisions → cords → branches
- Five terminal branches: musculocutaneous, axillary, radial, median, ulnar
The plexus runs roots → trunks → divisions → cords → branches. Cord Main branch Lateral Musculocutaneous (+ part of median) Medial Ulnar (+ part of median) Posterior Radial, axillary Applied
- Axillary lymph nodes — breast-cancer spread
- Brachial plexus injury (Erb’s, Klumpke’s)
🔑KEY POINTS TO REMEMBER- Axilla = pyramidal space; contents: axillary vessels, plexus cords, nodes.
- Plexus: roots (C5–T1) → trunks → divisions → cords → branches.
- 5 terminal branches: musculocutaneous, axillary, radial, median, ulnar.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The upper limb is supplied by the terminal branches of the brachial plexus; each nerve, when injured, produces a characteristic deformity.
Major Nerves
- Axillary (C5,6) — deltoid; lesion → loss of abduction
- Radial (C5–T1) — extensors; lesion → wrist drop
- Median (C6–T1) — flexors; lesion → ape hand
- Ulnar (C8,T1) — small muscles; lesion → claw hand
Common Sites of Injury
- Radial — mid-shaft of humerus (spiral groove)
- Ulnar — medial epicondyle
- Median — wrist (carpal tunnel)
- Axillary — surgical neck of humerus
Each nerve lesion denervates set muscles, giving a recognisable deformity. Nerve Deformity Lost movement Radial Wrist drop Extension Median Ape / pointing hand Thumb opposition Ulnar Claw hand Finger ab/adduction Axillary Loss of abduction Deltoid Applied
- Fractures cause specific nerve palsies
- Each nerve tested clinically by its deformity
🔑KEY POINTS TO REMEMBER- Radial → wrist drop; median → ape hand; ulnar → claw hand.
- Axillary → loss of abduction (surgical neck).
- Fracture site predicts the nerve injured.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The shoulder region connects the upper limb to the trunk; the arm contains the humerus with flexor and extensor compartments.
Shoulder Joint
- Ball-and-socket (glenohumeral)
- Most mobile, least stable → prone to dislocation
- Stabilised by the rotator cuff
Arm — Compartments
- Anterior (flexor) — biceps, brachialis, coracobrachialis (musculocutaneous n.)
- Posterior (extensor) — triceps (radial n.)
Key Neurovascular Relations
- Radial nerve in the spiral groove
- Axillary nerve at the surgical neck
The arm has a flexor and an extensor compartment with different nerves. Compartment Muscles Nerve Anterior Biceps, brachialis Musculocutaneous Posterior Triceps Radial Applied
- Shoulder dislocation → axillary nerve injury
- Mid-shaft humeral fracture → radial nerve
🔑KEY POINTS TO REMEMBER- Shoulder = ball-and-socket; most mobile, least stable.
- Arm: anterior flexors (musculocutaneous) vs posterior triceps (radial).
- Radial nerve in spiral groove; axillary at surgical neck.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The forearm contains flexor and extensor compartments; the cubital fossa is the triangular hollow in front of the elbow.
Forearm Compartments
- Anterior (flexor) — median & ulnar nerves
- Posterior (extensor) — radial nerve
Cubital Fossa — Boundaries
- Lateral — brachioradialis
- Medial — pronator teres
- Base — line between the epicondyles
Contents (lateral → medial: TAN)
- Biceps Tendon
- Brachial Artery
- Median Nerve
The cubital fossa holds the biceps tendon, brachial artery and median nerve. Boundary Structure Lateral Brachioradialis Medial Pronator teres Floor Brachialis, supinator Applied
- Venepuncture (median cubital vein)
- Brachial pulse; BP measurement
🔑KEY POINTS TO REMEMBER- Forearm: anterior flexors (median/ulnar) vs posterior extensors (radial).
- Cubital fossa boundaries: brachioradialis, pronator teres.
- Contents (lat→med): tendon, artery, nerve (TAN).
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The hand is the specialised terminal part of the upper limb, adapted for grip and fine movement, supplied by the median and ulnar nerves.
Muscles
- Thenar (thumb) — median nerve
- Hypothenar (little finger) — ulnar nerve
- Interossei & medial lumbricals — ulnar nerve
Nerve Supply
- Median — lateral 3½ fingers (palm)
- Ulnar — medial 1½ fingers
- Radial — dorsum (sensory)
Spaces & Sheaths
- Palmar spaces (thenar, midpalmar)
- Synovial flexor sheaths
The median and ulnar nerves share the hand’s muscles and sensation. Region Nerve Thenar Median Hypothenar Ulnar Interossei Ulnar Applied
- Carpal tunnel → median palsy
- Ulnar palsy → claw hand
🔑KEY POINTS TO REMEMBER- Thenar = median; hypothenar & interossei = ulnar.
- Median = lateral 3½ fingers; ulnar = medial 1½.
- Fine movement + grip.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The brachial plexus is a network of nerves (C5–T1) supplying the upper limb, arranged as roots, trunks, divisions, cords and branches.
Organisation (Real Texans Drink Cold Beer)
- Roots (C5–T1)
- Trunks (upper, middle, lower)
- Divisions (anterior, posterior)
- Cords (lateral, medial, posterior)
- Branches (five terminal)
The plexus is organised into five successive levels from roots to branches. Cord Terminal branch Lateral Musculocutaneous Medial Ulnar Posterior Radial, axillary Applied
- Erb’s palsy (upper, C5–6)
- Klumpke’s palsy (lower, C8–T1)
🔑KEY POINTS TO REMEMBER- Brachial plexus C5–T1: roots, trunks, divisions, cords, branches.
- Cords: lateral, medial, posterior.
- Erb’s (upper) vs Klumpke’s (lower) palsy.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The median nerve (C6–T1) is the ‘labourer’s nerve’, supplying most forearm flexors and the thenar muscles.
Supplies
- Most forearm flexors (except FCU & medial FDP)
- Thenar muscles, lateral 2 lumbricals
- Sensory — lateral 3½ fingers (palm)
Injury
- At wrist (carpal tunnel) → thenar wasting
- ‘Ape hand’ (loss of opposition)
- ‘Hand of benediction’ on making a fist
Median injury weakens the thumb and thenar muscles, giving the ape hand. Site Effect Wrist Thenar wasting, ape hand Elbow + loss of flexion Applied
- Carpal tunnel syndrome
- Test: thumb opposition
🔑KEY POINTS TO REMEMBER- Median nerve = forearm flexors + thenar muscles.
- Sensory: lateral 3½ fingers.
- Injury → ape hand, thenar wasting.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The radial nerve (C5–T1) supplies the extensors of the arm and forearm; injury causes wrist drop.
Supplies
- Triceps (arm)
- Extensors of the forearm (posterior compartment)
- Sensory — dorsum of hand (lateral)
Injury — Wrist Drop
- Site: mid-shaft of humerus (spiral groove)
- Loss of wrist and finger extension
- Wrist-drop deformity
Radial injury paralyses the extensors, so the wrist drops. Site Effect Axilla Triceps loss + wrist drop Spiral groove Wrist drop (triceps spared) Applied
- ‘Saturday night palsy’
- Humeral shaft fracture
🔑KEY POINTS TO REMEMBER- Radial nerve = all extensors + triceps.
- Injury at spiral groove → wrist drop.
- Saturday-night palsy; humeral fracture.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The rotator cuff is a group of four muscles that stabilise the shoulder joint by holding the humeral head in the glenoid cavity.
Muscles (SITS)
- Supraspinatus — initiates abduction
- Infraspinatus — lateral rotation
- Teres minor — lateral rotation
- Subscapularis — medial rotation
Four muscles grip the humeral head to stabilise the shoulder. Muscle Action Supraspinatus Abduction Infraspinatus Lateral rotation Teres minor Lateral rotation Subscapularis Medial rotation Applied
- Supraspinatus — commonly torn / impinged
- Painful arc syndrome
🔑KEY POINTS TO REMEMBER- SITS: supraspinatus, infraspinatus, teres minor, subscapularis.
- Stabilise the shoulder joint.
- Supraspinatus commonly injured.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The cubital fossa is the triangular depression in front of the elbow, containing important neurovascular structures.
Boundaries
- Lateral — brachioradialis
- Medial — pronator teres
- Base — intercondylar line
- Floor — brachialis, supinator
Contents (lateral → medial: TAN)
- Biceps Tendon
- Brachial Artery
- Median Nerve
A triangular hollow holding the biceps tendon, brachial artery and median nerve. Content Position Biceps tendon Lateral Brachial artery Middle Median nerve Medial Applied
- Venepuncture, brachial pulse, BP measurement
🔑KEY POINTS TO REMEMBER- Boundaries: brachioradialis (lat), pronator teres (med).
- Contents TAN: tendon, artery, nerve.
- Venepuncture & BP site.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
Carpal tunnel syndrome is compression of the median nerve within the carpal tunnel at the wrist.
Anatomy
- Carpal tunnel = carpal bones + flexor retinaculum
- Transmits the median nerve + flexor tendons
Features
- Pain and tingling in the lateral 3½ fingers
- Worse at night
- Thenar wasting (late)
- Tinel’s and Phalen’s signs positive
Compression of the median nerve in the tunnel causes the classic symptoms. Feature Detail Nerve Median Site Carpal tunnel (wrist) Signs Tinel, Phalen Applied
- Pregnancy, hypothyroidism, rheumatoid arthritis
- Treatment: splint, steroid, surgical release
🔑KEY POINTS TO REMEMBER- Median nerve compressed in the carpal tunnel.
- Tingling lateral 3½ fingers, worse at night, thenar wasting.
- Tinel/Phalen positive; treat by release.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.Definition
The anatomical snuffbox is a triangular depression on the radial side of the wrist, seen when the thumb is extended.
Boundaries
- Lateral — abductor pollicis longus & extensor pollicis brevis
- Medial — extensor pollicis longus
- Floor — scaphoid & trapezium
Contents
- Radial artery
- Superficial branch of the radial nerve
- Cephalic vein (in the roof)
A hollow over the scaphoid; the radial artery crosses its floor. Boundary Tendons Lateral APL, EPB Medial EPL Floor Scaphoid Applied
- Tenderness → scaphoid fracture (avascular necrosis risk)
- Radial pulse felt here
🔑KEY POINTS TO REMEMBER- Boundaries: APL/EPB (lat), EPL (med); floor = scaphoid.
- Contents: radial artery, radial nerve branch, cephalic vein.
- Tenderness → scaphoid fracture.
📚SOURCES: BD Chaurasia’s Human Anatomy; Gray’s Anatomy; Snell’s Clinical Anatomy.