Ulnar nerve
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What it means
Medial cord (C8–T1). Supplies most intrinsic hand muscles (interossei, medial two lumbricals, hypothenar, adductor pollicis) + FCU and the medial half of FDP; sensation over the medial 1½ digits. Vulnerable at the medial epicondyle/cubital tunnel and Guyon's canal → claw hand, weak finger abduction, positive Froment's sign.
Worked example
Elbow trauma → clawing of the ring/little fingers, wasted interossei, can't grip paper between thumb and index (Froment's) = ulnar nerve.
In the exam
After a fracture at the medial epicondyle a man develops clawing of the ring and little fingers, wasting between the metacarpals and a positive Froment's sign.
What settles it
Ulnar = intrinsics + medial 1½ digits; the 'ulnar paradox' (worse claw with DISTAL lesions). Median spares the intrinsics except LOAF.
Classically confused with
Median nerve
Source: TeachMeAnatomy — Ulnar nerve