When we hit our knee or elbow (funny bone) it hurts but why do we laugh?

I think there are two related issues here. If you have your shin hit it hurts, and it can really hurt. But if you hit your elbow you get a different kind of tingly sensation which is so strange that you can laugh. The tingling is the result of pressure to the brachial nerve which runs through the elbow structure.

Also, the bone in the upper arm is known as the humerus, so it is a bit of a pun to name the elbow the funny bone.