Even a light tap to the back of your elbow can send pain shooting down your forearm. You've hit the spot, your funny bone. Turns out, this spot is neither "funny" nor a "bone." In fact, you've just hit your ulnar nerve, which controls feeling in your pinky and ring fingers, and helps control the muscles in the wrist, as well as parts of the hand.
This nerve travels from your neck down your upper arm, wrapping around the elbow joint on its way to the hand. In most spots along this route the ulnar nerve stays hidden within muscles and other tissue. But when it passes through your elbow joint, the nerve is particularly close to the skin — making it a vulnerable target.
One idea for how the ulnar nerve got its silly name is the fact that the nerve also runs through the humerus bone in your upper arm. No joke.