Anatomy Guide › Upper limb
Ulnar Nerve
Everyone has met the ulnar nerve, usually without wanting to. It is the nerve behind the 'funny bone': at the inner side of the elbow it passes through a shallow groove on the humerus with almost no padding, and a knock there fires electric tingling down the forearm into the ring and little fingers. That distribution is no accident — those two fingers are precisely the ulnar nerve's sensory territory.
The nerve arises from the brachial plexus at the shoulder, travels down the inner arm, rounds the elbow through that exposed groove (the cubital tunnel), and continues along the ulnar side of the forearm into the hand. There it does its most important work. The ulnar nerve drives most of the hand's intrinsic muscles — the small muscles between the metacarpals that spread and close the fingers, the muscles of the little-finger pad, and the muscle that lets the thumb pinch powerfully. Piano runs, typing, card shuffling, and a firm precision grip are all ulnar-powered skills.
Because it runs so exposed, the ulnar nerve is the second most commonly compressed nerve in the arm after the median. Habitual leaning on the elbow or prolonged bending — the phone-to-ear posture — can irritate it in the cubital tunnel, numbing the pinky side of the hand. Longstanding compression weakens the intrinsic muscles and can produce 'claw hand,' where the ring and little fingers curl. Cyclists know a wrist-level version from handlebar pressure.
In Anamo, the ulnar nerve traces the little-finger lane of the arm map, from inner elbow to pinky. Pair it mentally with the ulna and ulnar artery: three parallel structures, one lane, easy heat to read.
- Striking it at the elbow causes the 'funny bone' sensation
- Powers most of the small muscles of the hand
- Supplies feeling to the ring and little fingers
- Commonly compressed at the elbow's cubital tunnel
Think you could find the ulnar nerve on a 3D model? Play Anamo and test yourself — every guess is color-coded by how close it lands to the mystery structure.