The ulna is one of the two long bones in your forearm, running from your elbow to your wrist on the pinky side of your arm. If you hold your arm out straight with your palm facing up, the ulna is the bone on the inner edge.

At your elbow, the ulna forms that pointy bump you can feel when you bend your arm. That bump is actually the top of the ulna, and it's what you're really feeling when you accidentally hit your “funny bone” (though there's nothing funny about that tingling sensation!). The ulna works together with the other forearm bone, called the radius, to help your arm twist and rotate. When you turn a doorknob or wave goodbye, both bones are working in tandem.

The ulna is thicker and stronger at the elbow end but becomes thinner as it reaches your wrist. Next time you rest your elbow on a table, you're resting on your ulna.