Short answer: learn the brachial plexus in five layers, in order, and draw it from memory once a day for a week. Roots C5 to T1, three trunks, divisions, three cords, five branches. Most students fail because they try to swallow the whole diagram at once instead of building it layer by layer.
The five layers in plain words
Start with the roots: the ventral rami of C5, C6, C7, C8 and T1. Five roots. The mnemonic everyone uses is Randy Travis Drinks Cold Beer, one word per root from top to bottom. Next, the roots join into three trunks: upper (C5-C6), middle (C7 alone), lower (C8-T1). Think of it like pairing off at a dance with an odd number of people: C7 is left standing alone in the middle.
Each trunk then splits into an anterior and a posterior division. Anterior divisions feed the flexor muscles, posterior divisions feed the extensors. The divisions regroup into three cords, named by where they sit around the axillary artery: lateral, medial and posterior. Finally, the cords give off the five terminal branches, remembered as MARMU: musculocutaneous, axillary, radial, median and ulnar. The whole order is Read That Damn Cadaver Book: Roots, Trunks, Divisions, Cords, Branches.
The draw-it-from-memory method
Day one, copy the diagram from your textbook slowly, saying each layer out loud as you draw it. Day two, try it from memory on a blank page. You will get stuck. That stuck moment is the learning. Check the book, fill the gap, and draw it again. Repeat daily for a week. By day five most students can draw the full plexus in under three minutes, and it stays.
Two rules make this work. First, always draw in the same order, roots to branches, never backwards. Second, label the clinical injuries on the same diagram, not on a separate page. When Erb's and Klumpke's sit on the drawing itself, you remember them with the anatomy instead of as extra facts.
The two injuries examiners love
Erb's palsy is an upper trunk injury (C5-C6). The arm hangs limply in the waiter's tip position because shoulder abduction, lateral rotation and elbow flexion are all lost. Klumpke's palsy is a lower trunk injury (C8-T1) and shows up as a claw hand, because the small muscles of the hand lose their nerve supply. If you can point to both on your drawing and say which roots are hit, you have the viva question covered.
Make it stick past the exam
Drawing it once is not enough. The plexus fades fast if you never test it again. Put each branch and each injury on a flashcard and review them on a schedule instead of re-reading the diagram. Ominsol's flashcards are built for exactly this kind of recall, and our guide to spaced repetition for MBBS shows the review schedule that keeps facts alive till exam day. For the next anatomy headache, read our cranial nerves mnemonics next, and if your whole subject needs a plan, our 30-day anatomy revision plan puts it all in order.