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Lumbar disc herniation and nerve roots. Posterior view of L4–S1 (right-sided roots shown). Lumbar roots exit below their own pedicle, so a posterolateral L4–L5 herniation (1) compresses the traversing L5 root and a far-lateral herniation (2) compresses the exiting L4 root.
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Lumbar puncture anatomy. Sagittal schematic (not to scale): the cord ends at about L1–L2, the dural sac at about S2. The needle enters at L3–L4, just above the intercristal line (≈ L4), well below the conus.
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Suboccipital triangle. Posterior view with the superficial muscles removed. Rectus capitis posterior major, obliquus capitis superior and obliquus capitis inferior bound the triangle; the vertebral artery and suboccipital nerve (C1) lie in its floor on the posterior arch of the atlas. The greater occipital nerve (C2) emerges below obliquus capitis inferior and is not a content of the triangle.
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Vertebral column (lateral view). Left lateral view, anterior to the left. Cervical and lumbar lordoses are secondary curvatures; thoracic and sacral kyphoses are primary. Landmark levels vary by about one segment between people, so use them as guides, not rules.
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Vertebral venous plexus (Batson). A: lumbar cross-section, oriented as on axial CT. The internal plexus lies in the epidural space; the external plexus lies outside the vertebra. B: the plexus is a valveless channel from the skull to the pelvis, which is why pelvic tumors (classically prostate) and infections can reach the vertebrae.
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Coronary arteries (anterior view). Right-dominant pattern shown; dashed vessels run on the posterior/inferior surface. ECG territories: LAD → V1–V4 (anteroseptal); circumflex → I, aVL, V5–V6 (lateral); RCA → II, III, aVF (inferior).
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Cardiac auscultation areas. Classic listening posts. These are where each valve is heard best, not where the valves lie anatomically. Count interspaces down from the 2nd rib at the sternal angle.
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Internal thoracic artery (anterior view). Drawn as if seen through the chest wall; the arteries run on its deep surface about 1 cm lateral to the sternum. Each divides in the 6th intercostal space into the musculophrenic and superior epigastric arteries. The superior epigastric anastomoses with the inferior epigastric in the rectus sheath, a subclavian-to-iliac collateral route (for example in coarctation).
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Divisions of the mediastinum. Sagittal view, anterior on your left. The plane through the sternal angle and the T4/T5 disc divides the superior from the inferior mediastinum; the pericardium splits the inferior part into anterior, middle and posterior. Masses follow the compartments: anterior = the 4 T's, middle = lymph nodes and cysts, posterior = neurogenic tumors. Radiologists increasingly use a three-compartment CT model (prevascular, visceral, paravertebral) that maps onto these.
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Hepatic portal system. Portal veins (purple) drain the gut, spleen and pancreas to the liver; systemic veins in blue. Numbered sites are portosystemic anastomoses that dilate in portal hypertension. Tap a label to open its page.
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Arterial supply of the gut. The three unpaired anterior branches of the abdominal aorta and their territories, with vertebral levels and where visceral pain from each region is felt.
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Inguinal region from inside (Hesselbach triangle). Right side seen from inside the abdomen, as at laparoscopy. The inferior epigastric vessels separate indirect hernias (lateral, through the deep ring) from direct hernias (medial, through the inguinal triangle). Femoral hernias pass below the inguinal ligament, medial to the femoral vein. The inguinal canal and superficial ring lie in front of this plane (dashed).
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Referred visceral pain. Visceral pain is poorly localized and felt in the dermatomes that share spinal segments with the organ's afferent fibers. Pain becomes sharp and localized once the parietal peritoneum is involved (appendicitis: periumbilical → RLQ). Zones are approximate and vary between people.
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Branches of the internal iliac artery. Usual branching pattern (it varies between people). Posterior-division branches are dashed; the superior gluteal passes above piriformis, the inferior gluteal and internal pudendal below it. Tap a label to open its page.
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Perineum: urogenital and anal triangles. Inferior view with the patient in lithotomy (anterior at the top). A line between the ischial tuberosities divides the urogenital triangle from the anal triangle; the pudendal canal runs in the lateral wall of each ischioanal fossa.
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Brachial plexus. Roots (ventral rami C5–T1) → trunks → divisions → cords → terminal branches. Dashed lines = posterior divisions, posterior cord and its branches. Selected collateral branches shown. Tap a nerve name to open its page.
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Upper limb dermatomes (anterior view). Schematic of the commonly taught pattern. Adjacent dermatomes overlap and published maps disagree at the borders, so check against your textbook. The C6–C8 ASIA key points are tested on the dorsal surface of the digits.
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Rotator cuff (SITS). Right glenoid seen from the side with the humerus removed. The cuff covers the top, back and front of the joint but not its inferior part, which is why most dislocations are anterior–inferior. The table summarizes attachments, nerves, actions and bedside tests.
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Carpal bones (right hand, palmar view). Thumb on the left. The flexor retinaculum (dashed) is anchored to the scaphoid tubercle and trapezium laterally and to the pisiform and hook of hamate medially, forming the roof of the carpal tunnel. Highlighted bones are the high-yield ones: scaphoid (fracture), lunate (dislocation) and hamate (hook fracture).
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Cubital fossa (right, anterior view). Lateral (thumb side) on your left. Borders: the line between the epicondyles above, brachioradialis laterally and pronator teres medially. Contents lateral to medial: biceps Tendon, brachial Artery, median Nerve (TAN), with the radial nerve deep at the lateral edge. The brachial pulse is just medial to the tendon, and the median cubital vein in the roof is the usual venipuncture site, superficial to the bicipital aponeurosis.
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Lower limb dermatomes and key muscles. Right lower limb, anterior view (medial = your right). Dots are ASIA key sensory points; the table gives the key muscle action and reflex for each root. Dermatome maps differ between sources.
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Compartments of the leg. Schematic mid-leg cross-section: four compartments separated by bone, the interosseous membrane and intermuscular septa, each with its own nerve. Compartment syndrome most often affects the anterior compartment.
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Femoral triangle (right, anterior view). Lateral on your left. The base is the inguinal ligament, the borders are sartorius (lateral) and adductor longus (medial), and the floor is iliopsoas and pectineus. Lateral to medial: Nerve (outside the femoral sheath), Artery, Vein, Empty space (femoral canal), Lymphatics. The pulse is felt just below the mid-inguinal point, with the vein just medial to it; a femoral hernia comes through the femoral canal.
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Right tibial plateau from above. Femur removed, anterior at the top, medial on your left. The medial meniscus is C-shaped and fixed to the MCL, so it moves less and tears more often; the lateral meniscus is nearly a ring and is separated from the LCL by the popliteus tendon. The cruciates are named for their tibial attachments: the ACL runs from the anterior intercondylar area to the lateral femoral condyle, the PCL from the posterior area to the medial condyle. Only the outer third (red zone) of each meniscus has a blood supply.
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H-pattern test of the extraocular muscles. Examiner's view of the patient's right eye (patient's right = your left). Each end-point is the gaze position that isolates one muscle; gold dots = CN VI and CN IV, red dots = CN III. The obliques are tested with the eye adducted, the superior and inferior recti with it abducted.
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Triangles of the neck. Right lateral view, face to the right (schematic, not to scale). Sternocleidomastoid separates the anterior triangle (submandibular, carotid, muscular; submental in the midline) from the posterior triangle (occipital, omoclavicular). The dashed common carotid runs deep to sternocleidomastoid.
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Foramina of the cranial base. Internal view from above, anterior at the top. Each foramen is drawn on both sides and labelled on one. The carotid canal runs inside the petrous bone (dashed) and opens at its apex, where the internal carotid artery crosses above the cartilage-filled foramen lacerum.
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Course of the recurrent laryngeal nerves. Anterior view, patient's right on your left. The right RLN hooks under the right subclavian artery in the root of the neck; the left hooks under the aortic arch beside the ligamentum arteriosum, so it is longer and runs in the chest. Both climb in the tracheoesophageal groove past the inferior thyroid arteries to supply every intrinsic laryngeal muscle except cricothyroid (external laryngeal nerve). Hoarseness after thyroidectomy, or from a lung cancer or aortic aneurysm on the left, points to the RLN.
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Visual pathway and field defects. View from above, anterior at the top. Nasal retinal fibers cross at the chiasm; the Meyer loop (temporal lobe) carries the upper field and the parietal radiation the lower field. The numbered left-sided lesions produce the field defects in the table (patient's view, red = lost).
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Circle of Willis and vertebrobasilar system. Inferior view, anterior at the top. The internal carotids (anterior circulation) and basilar artery (posterior circulation) are joined by the communicating arteries; CN III passes between the PCA and SCA. Red dots mark common berry aneurysm sites. A complete, symmetric circle is present in only a minority of people.
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Territories of the cerebral arteries. Lateral surface of the left hemisphere and medial surface of the right. The MCA supplies the face and arm cortex and the language areas; the ACA the medial leg area; the PCA the occipital lobe. Territory borders vary between people.
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Spinal cord tracts (cross-section). Cervical cord, dorsal at the top. Dorsal columns and lateral corticospinal tract serve the same side of the body; the spinothalamic tract serves the opposite side because its fibers cross in the anterior white commissure (dashed green) within 1–2 segments.
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Flow of cerebrospinal fluid. Lateral ventricles → foramina of Monro → third ventricle → cerebral aqueduct → fourth ventricle → Magendie and Luschka → subarachnoid space → arachnoid granulations → superior sagittal sinus. A block anywhere inside the ventricles causes noncommunicating (obstructive) hydrocephalus, with the ventricles dilated upstream of the block; failed absorption at the granulations causes communicating hydrocephalus.
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Upper vs lower motor neuron facial palsy. The forehead part of each facial nucleus gets corticobulbar input from both cortices; the lower-face part only from the opposite cortex. A stroke in the cortex or internal capsule (A) therefore weakens the opposite lower face and spares the forehead. A facial nerve lesion such as Bell palsy (B) weakens the whole of that side of the face, forehead included. Forehead involved = peripheral; forehead spared = central.
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Where the cranial nerves leave the brainstem. Ventral view. III leaves the interpeduncular fossa of the midbrain; IV is the only nerve to leave from the back (dashed); V leaves the lateral pons; VI the pontomedullary junction near the midline; VII and VIII the cerebellopontine angle; IX and X the postolivary sulcus; XII the preolivary sulcus between pyramid and olive; and XI rises from the upper cervical cord. Nuclei follow the same levels: III–IV midbrain, V–VIII pons, IX–XII medulla.