The "funny bone"
Ulnar nerve · nervus ulnaris
The nerve that runs your little finger, and the reason a knock on the elbow feels electric.
What it does
The ulnar nerve starts in your neck and runs all the way down the inside of your arm to your hand. It carries feeling from your little finger and half of your ring finger. It also works most of the small muscles inside your hand, the ones that let you spread your fingers, grip a pen and do fine, careful work.
Surprising fact
The "funny bone" isn't a bone at all. It is the spot where the ulnar nerve slides around the back of your elbow with almost nothing protecting it, the largest nerve in the body to sit so exposed.
Why it matters
That zing down to your little finger when you bump your elbow is the nerve being squashed against bone. Leaning on your elbows for a long time, or sleeping with them tightly bent, can press on it too, which is why your little finger sometimes tingles.
Nearby
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Sources
Drafted with AI help; awaiting a human fact-check against these sources.
Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.