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High-Yield Anatomy Review

Jun 14, 2025

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Overview

This lecture is a comprehensive "one-shot" review covering high-yield anatomy topics for medical entrance exams, focusing on embryology, limbs, neuroanatomy, histology, and key clinical correlations.

Embryology: Germ Layers & Derivatives

  • Three germ layers: ectoderm, mesoderm, endoderm.
  • Notochord (from axial mesoderm) induces ectoderm to form neural tube (CNS) and neural crest cells (PNS, head/neck structures).
  • Mesoderm divides into paraxial (forms somites), intermediate (urogenital system), and lateral plate (limb skeleton, muscles).
  • Somites form dermis (back), axial skeleton (vertebrae, ribs), and skeletal muscles (except most head/neck).
  • Lateral plate mesoderm forms limb dermis, appendicular skeleton, smooth and cardiac muscle.
  • Diaphragm develops from four sources: septum transversum, pleuroperitoneal membrane, dorsal mesentery of esophagus, body wall.

Pharyngeal Arches, Clefts & Pouches

  • Pharyngeal arches give rise to muscles, arteries, bones of head/neck.
  • 1st cleft → external auditory canal; 1st pouch → middle ear cavity, eustachian tube.
  • 2nd pouch → palatine tonsil; 3rd pouch → thymus and inferior parathyroid; 4th pouch → superior parathyroid.
  • Persistent cervical sinus can cause branchial cyst.
  • Arch arteries form parts of the aorta, carotids, subclavian, pulmonary arteries, and ductus arteriosus.

Upper & Lower Limb Anatomy

  • Humeral fractures: surgical neck (axillary nerve), mid-shaft (radial), supracondylar (median/anterior interosseous), medial epicondyle (ulnar nerve).
  • Scapular muscles: rhomboids (retract/elevate scapula), levator scapulae (elevates scapula), innervated by dorsal scapular nerve.
  • Hand muscles: thenar/hypothenar muscles, lumbricals (lateral 2 median, medial 2 ulnar), interossei (PAD—adduct, DAB—abduct), adductor pollicis—ulnar nerve.

Brachial Plexus & Nerve Injuries

  • Brachial plexus formed by C5-T1; major cords: lateral (musculocutaneous), posterior (radial), medial (ulnar).
  • Erb's palsy (C5-C6): adducted shoulder, extended/pronated elbow.
  • Klumpke's palsy (C8-T1): claw hand, possible Horner's syndrome.
  • Radial nerve injury: wrist drop; median nerve: ape hand, hand of benediction; ulnar: claw hand.

Histology High-Yield Features

  • Cardiac muscle: branched fibers, central nuclei, intercalated discs (gap junctions).
  • Skeletal muscle: peripheral nuclei, cross-striations.
  • Lymph node: cortex/medulla, subcapsular sinus, paracortex (T cells).
  • Palatine tonsil: lymphoid follicles, crypts, stratified squamous epithelium.
  • Spleen: white pulp (lymphoid), red pulp (RBC), central arteries in follicles.
  • Thymus: lobules, Hassall’s corpuscles.

Lower Limb & Pelvis

  • Important nerves in lumbar plexus: femoral, obturator, lateral cutaneous.
  • Hip muscles: gluteus medius/minimus (abduction/medial rotation), gluteus maximus (extension).
  • Sciatic nerve divides into tibial (posterior compartment, plantar flexion) and common peroneal (lateral/anterior compartment, dorsiflexion).
  • Trendelenburg sign: pelvic drop due to superior gluteal nerve injury.
  • Superficial/deep perineal pouches: understand urine extravasation with urethral injuries.

Abdomen & Perineum

  • Epiploic (Winslow’s) foramen: connection between greater & lesser sacs; portal triad anterior, IVC posterior.
  • Pelvic diaphragm (levator ani: pubococcygeus, iliococcygeus; ischiococcygeus), supports pelvic organs.
  • Perineal body: central tendon of perineum, convergence point for several muscles.

Neuroanatomy Essentials

  • Cranial nerve columns: GSE, SVE, GVE, GSA, SSA, SVA, GVA.
  • Key nuclei: Edinger-Westphal (III), salivatory (VII, IX), dorsal motor (X), nucleus ambiguus (IX, X, XI).
  • Cavernous sinus contents: III, IV, V1, V2 (lateral wall); VI and ICA inside.
  • Brown-Sequard syndrome: ipsilateral motor/vibration loss, contralateral pain/temp loss below lesion.

Key Terms & Definitions

  • Somite — segmental blocks of paraxial mesoderm forming muscle, dermis, vertebrae.
  • Neural Crest Cells — embryonic cells forming PNS and head/neck tissues.
  • Pharyngeal Arch — embryonic structure giving rise to nerves, muscles, arteries in head/neck.
  • Epiploic Foramen — passage connecting greater and lesser sacs of the peritoneum.
  • Trendelenburg Sign — pelvic drop on contralateral side of gluteus medius lesion.
  • Perineal Body — fibromuscular node in perineum anchoring several muscles.

Action Items / Next Steps

  • Review provided PDF/slides for image-based revision.
  • Practice identifying key structures in histology and cross-sectional anatomy.
  • Take the upcoming free mock test on May 16.
  • Revise nerve injury patterns and clinical correlations.
  • Focus on high-yield embryology (arches, pouches, derivatives) and neuroanatomy columns for exams.

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