What is the funny bone?
The funny bone is not a bone. It is the ulnar nerve, which runs close to the skin at the back of the elbow. Hitting it causes a tingling, painful feeling down the arm.
The ulnar nerve carries signals between the brain and the forearm and hand, especially the ring and little fingers. At the elbow, it passes through a groove called the cubital tunnel, where it is protected only by skin and fat. A knock there squeezes the nerve against the bone, causing a sudden electric-shock sensation.
The feeling often spreads to the little finger and ring finger, because those are the areas the ulnar nerve supplies. The sensation usually fades within a minute. Leaning on the elbow for a long time can also press on the nerve, causing numbness in the same fingers.
Why is it called funny?
No one knows for sure. One popular theory is that it is a pun on the humerus, the upper arm bone, which sounds like humorous. Another is simply that the strange tingling feels funny rather than like ordinary pain.
Did You Know?
Ongoing numbness or weakness in the little and ring fingers can be caused by ulnar nerve entrapment and is worth checking with a doctor.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.