Why does it hurt when you hit your funny bone?

The ulnar nerve.

The funny bone is actually the ulnar nerve, which runs from the neck down the arm to the hand. It's responsible for providing sensation to the pinky and ring fingers, as well as the inside of the forearm.

When you hit your elbow, you're actually hitting the ulnar nerve where it passes over the bony prominence at the point of the elbow. The force of the impact can compress or irritate the nerve, which can cause a sharp, shooting pain down the arm and into the hand.

The pain is usually temporary and will go away on its own within a few minutes, but in some cases, it can last for several days. In rare cases, damage to the ulnar nerve can cause permanent nerve damage, leading to numbness or tingling in the affected fingers.