NEW Added to close a syllabus gap — the syllabus names thorax, spine, peripheral nervous and vascular systems, and surface markings.

Anatomy: thorax, abdomen & access

Surface markings, the thorax, cranial nerves, and the vascular anatomy behind central access and arterial lines.

Surface markings to know cold

Landmark	Level	What is there
Cricoid cartilage	C6	Start of trachea and oesophagus; the only complete ring
Sternal angle (of Louis)	T4/T5	Carina · aortic arch begins and ends · azygos vein joins SVC · 2nd costal cartilage
Xiphisternum	T9	Dermatome T6 at the xiphisternum
Transpyloric plane	L1	Pylorus · pancreatic neck · coeliac plexus (T12–L1) · renal hila · SMA origin
Umbilicus	L3/L4	Dermatome T10
Tuffier's line (iliac crests)	L4	L4 body or L4/5 space; unreliable, often reads a space high
Aortic bifurcation	L4	Into common iliacs

Dermatomes: C6 thumb · T4 nipple · T6 xiphisternum · T10 umbilicus · L1 inguinal ligament · S2–4 perineum.

Motor supply: phrenic nerve, C3, 4, 5 — "keeps the diaphragm alive". Sensory to the central portion is also phrenic; the periphery is supplied by intercostal nerves.
Openings: T8 — IVC (and right phrenic) · T10 — oesophagus (and vagi) · T12 — aorta (with thoracic duct and azygos). Mnemonic: "vena cava 8, oesophagus 10, aortic hiatus 12".
Diaphragmatic irritation refers pain to the shoulder tip (C4) — relevant after laparoscopy.

Neurovascular bundle runs in the subcostal groove, order from above down: Vein, Artery, Nerve (VAN). Insert needles just above the rib below to avoid it.
Chest drain — the "triangle of safety": lateral border of pectoralis major, anterior border of latissimus dorsi, and a line above the 5th intercostal space.
Trachea: C6 to the carina at T4/5, 10–12 cm long, 16–20 incomplete cartilage rings. Right main bronchus wider, shorter and more vertical (25° vs 45°).
Thoracic duct drains into the junction of the left subclavian and internal jugular veins — hence chylothorax risk with left-sided central access.

Site	Relations	Complications
Internal jugular	Lateral and slightly anterior to the carotid at the cricoid; within the carotid sheath, in the triangle between the sternal and clavicular heads of sternocleidomastoid	Carotid puncture, pneumothorax, thoracic duct injury (left)
Subclavian	Vein passes ANTERIOR to the anterior scalene; artery and brachial plexus pass POSTERIOR to it	Pneumothorax (highest risk), subclavian artery puncture — not compressible
Femoral	From lateral to medial: NAVY — Nerve, Artery, Vein, Y-fronts. Vein is medial to the artery	Infection, thrombosis, arterial puncture
Radial artery	Lateral to flexor carpi radialis; ulnar supplies the deep palmar arch	Thrombosis, distal ischaemia; Allen's test is unreliable

Antecubital fossa — from medial to lateral: median nerve, brachial artery, biceps tendon ("My Brother Throws"). The median cubital vein crosses superficially.
Ultrasound guidance is now standard for internal jugular access and reduces complications significantly.

Nerve	Relevance
V — Trigeminal	Sensation to the face and anterior tongue (lingual, V₃); afferent limb of the oculocardiac reflex (V₁)
VII — Facial	Taste anterior ⅔ via chorda tympani; facial muscles
IX — Glossopharyngeal	Sensation and taste posterior ⅓; oropharynx and gag reflex; carotid body and sinus afferents; stylopharyngeus
X — Vagus	Larynx (SLN and RLN); efferent limb of the oculocardiac reflex; aortic body afferents; all pharyngeal muscles except stylopharyngeus
XI — Accessory	Sternocleidomastoid and trapezius; contributes to the pharyngeal plexus
XII — Hypoglossal	All tongue muscles except palatoglossus; carries C1 fibres to thyrohyoid

Innervated by T7–L1: thoracoabdominal nerves T7–T11, subcostal T12, iliohypogastric and ilioinguinal L1.
Layers, superficial to deep: skin, Camper's and Scarpa's fascia, external oblique, internal oblique, transversus abdominis, transversalis fascia, peritoneum.
TAP block deposits between internal oblique and transversus abdominis — somatic wall analgesia only, no visceral cover.
Rectus sheath block targets terminal branches of T9–T11 between rectus muscle and the posterior sheath — for midline incisions.
Arcuate line: below it the posterior rectus sheath is absent — the reason rectus sheath blocks are done above it.