Why Does It Hurt So Much To Hit Your Funny Bone? - BBC Future

There’s no pain quite like the one you experience when you hit your funny bone. But what is going on to create such an odd feeling?

Everybody knows that smacking your funny bone isn’t all that funny, but did you know that the prickling feeling you feel from smacking it isn’t from your bones at all? Instead, the decidedly unpleasant sensation comes from the ulnar nerve, a set of sensitive fibres that runs along your arm and passes behind your elbow joint.

It isn’t actually clear how the funny bone got its name. Some say that it’s a play on words since the upper arm bone, the one between your elbow and shoulder, is called the humerus. Others instead argue that the name is derived from the funny, tingly feeling you get when you strike it the wrong way. We might not know exactly why it’s called the funny bone, but we do know why it hurts so much to hit it.

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The ulnar nerve begins in the spine and branches out through the shoulder and down the arm, ending ultimately in the little finger and the adjacent ring finger. As the bundle of neurons travels down your arm, layers of bone and muscle offer protection as it sends and receives signals to and from the muscles of the forearm and the hand.

The problem is that as the ulnar nerve passes the elbow it travels behind a knob of the humerus called the medial epicondyle and through a small, 4mm-long channel called the cubital tunnel, right next to the olecranon, the bony hook where the radius and ulna meet the humerus. And in that spot, the nerve is sandwiched between the bone and the skin, without much in the way of padding or protection.