Radial nerve
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What it means
Posterior cord (C5–T1). Supplies all extensors of arm/forearm (triceps, wrist & finger extensors, supinator) → loss gives WRIST DROP; sensation over the dorsal first web space. Vulnerable in the radial groove of the humerus (mid-shaft fracture) and to compression — 'Saturday-night palsy' (arm draped over a chair while intoxicated).
Worked example
Intoxicated man sleeps with his arm over a chair → wakes unable to extend wrist/fingers, numb base of thumb (a high lesion still spares triceps).
In the exam
After sleeping with his arm over a hard edge while intoxicated, a man cannot extend his wrist or fingers and the skin at the base of his thumb is numb.
What settles it
Radial = EXTENSION (wrist drop) + dorsal web-space sensation. Its deep branch (posterior interosseous) gives finger-drop but NO sensory loss and spares wrist extension.
Classically confused with
Musculocutaneous nerve
Source: TeachMeAnatomy — Radial nerve