Anatomy: applied relations, embryology and lesion localisation
What the Primary exam tests in Anatomy
Anatomy at NPMCN Primary level is applied rather than purely descriptive: you must name structures, their relations, their embryological origin and the clinical deficit produced when they fail. Recurring areas are the brachial and lumbosacral plexuses, the femoral and inguinal regions, the mediastinum, the pharyngeal arches and the cranial nerves.
Core rules to hold
- Relation before name. Learn structures inside their anatomical box: in the femoral triangle, lateral to medial, lie nerve, artery, vein, empty space (femoral canal) and lymphatics - NAVEL.
- Embryology predicts adult anatomy. Each pharyngeal arch carries its own nerve, artery and muscle group. The left recurrent laryngeal nerve hooks under the 6th-arch derivative (ligamentum arteriosum); the right hooks under the right subclavian artery.
- Segmental supply differs from peripheral nerve supply. Dermatomes and myotomes follow spinal roots; a peripheral nerve may carry fibres from several roots, which is why root and nerve lesions produce different patterns.
Worked example
A footballer fractures the neck of the fibula. He cannot dorsiflex or evert the foot, has sensory loss over the dorsum of the foot and lateral leg, and walks with a high-stepping foot drop. Reasoning: the common fibular nerve winds around the fibular neck, so it is injured there; its deep branch supplies tibialis anterior (dorsiflexion) and its superficial branch supplies fibularis longus and brevis (eversion). Inversion is preserved because tibialis posterior is supplied by the tibial nerve. Diagnosis: common fibular nerve palsy.
Traps that cost marks
- Mixing median and ulnar claw hand: an ulnar lesion claws the 4th and 5th digits, while a high median lesion gives the ape hand with thenar wasting.
- Naming the saphenous nerve as a motor nerve of the thigh - it is purely sensory.
- Forgetting that the femoral nerve lies outside the femoral sheath while the artery and vein lie within it.