Anatomy Guide › Upper limb
Radial Nerve
The radial nerve is the largest branch of the brachial plexus and the arm's extension specialist. Every muscle that straightens your elbow, cocks your wrist back, or opens your fingers from a fist answers to it. Without the radial nerve you could still make a fist — but you could not release it, aim it, or stabilize the wrist behind it, which is why radial nerve injuries are so disabling despite leaving grip muscles untouched.
The nerve's route is its story. Leaving the armpit, it spirals diagonally around the back of the humerus in a bony groove, hugging the shaft where a mid-arm fracture — or even deep pressure — can injure it. The classic result is 'wrist drop': the hand hangs limp at the wrist, unable to lift. The condition's nicknames chart its causes — 'Saturday night palsy' from an arm slung over a chair back during deep sleep, 'crutch palsy' from poorly fitted crutches pressing into the armpit.
Below the elbow the nerve splits in two: a sensory branch that runs down the thumb side of the forearm to feel the back of the hand and thumb web, and a deep motor branch that dives into the supinator muscle and fans out to the extensor muscles of the wrist and fingers. The small patch of skin between thumb and index finger on the back of the hand is the radial nerve's signature sensory territory — the spot examiners test first.
In Anamo, the radial nerve ties together the back-of-arm map: triceps territory, the spiral groove of the humerus, the supinator, and the extensor compartment. When heat readings trail along the back of the forearm, you are in radial country.
- Controls every muscle that straightens the elbow, wrist, and fingers
- Spirals in direct contact with the humerus, where fractures can injure it
- Injury causes 'wrist drop' — inability to lift the hand at the wrist
- Feels the back of the hand at the thumb web
Think you could find the radial nerve on a 3D model? Play Anamo and test yourself — every guess is color-coded by how close it lands to the mystery structure.