Anatomy High Yield Notes
Mastering clinically relevant structures for USMLE Step 1 (2026)
Anatomy typically accounts for 15-20% of Step 1. The focus is no longer on pure memorization but on integrated clinical vignettes. High-yield areas include nerve injuries, vascular relations, and embryologic correlations.
Study Strategy: Visualize structures → Link to function → Apply to clinical vignettes.
1. Brachial Plexus (C5-T1)
The plexus is divided into Roots → Trunks → Divisions → Cords → Branches.
Mnemonic: Robert Taylor Drinks Cold Beer (Roots, Trunks, Divisions, Cords, Branches)
Major Terminal Branches (MARMU)
- Musculocutaneous (C5-C7): Elbow flexion, supination. Sensory: Lateral forearm.
- Axillary (C5-C6): Shoulder abduction (Deltoid). Risk: Surgical neck fracture.
- Radial (C5-T1): Wrist/Finger extension. Risk: Midshaft humerus fracture (Wrist Drop).
- Median (C6-T1): Thenar muscles, lateral 3.5 digits. Risk: Carpal Tunnel.
- Ulnar (C8-T1): Intrinsic hand muscles. Risk: Medial epicondyle injury (Claw Hand).
Clinical Scenario: A neonate presents with an adducted, internally rotated arm and extended elbow following a difficult delivery (shoulder dystocia).
Diagnosis: Erb’s Palsy (C5-C6 "Waiter's Tip").
Diagnosis: Erb’s Palsy (C5-C6 "Waiter's Tip").
2. Cranial Nerves (I - XII)
High yield focus: Function, Foramina, and classic lesions.
| CN | Name | High Yield Lesion |
|---|---|---|
| CN III | Oculomotor | "Down and out" eye; fixed dilated pupil in compression. |
| CN VII | Facial | Bell's Palsy (Full face); Hyperacusis (loss of stapedius). |
| CN X | Vagus | Uvula deviates away from the side of lesion. |
| CN XII | Hypoglossal | Tongue deviates toward the side of lesion. |
3. Dermatomes & Myotomes
Key Landmarks
- T4: Nipple Line
- T10: Umbilicus
- L4: Medial Malleolus (Leg)
- S2-S4: Saddle Area (Perianal)
Myotomes
- C5: Shoulder Abduction
- C6: Wrist Extension
- L4: Ankle Dorsiflexion
- S1: Ankle Plantarflexion
Summary Study Tips
- Draw the brachial plexus daily until it's muscle memory.
- Use Anki for foramina (Rotundum, Ovale, Spinosum).
- Always check "pupil sparing" in CN III lesions to differentiate ischemia from compression.