The funny bone. A spot that strikes fear into the hearts of even the strongest humans, smacking that dreaded (yet annoyingly exposed) bit of your elbow on the door as you walk past turns a functional arm into a screaming limb made of Jell-O. Despite this glaring weakness, it resides in an area with an extremely low number of pain receptors. So, what is the funny bone, and why does it hurt so much when you hit it? What is the funny bone? As with most nicknames, the name "funny bone" is actually completely wrong – it's more of a "funny nerve". The ulnar nerve is one of the three main nerves in the arm. It runs from the neck, all the way through the bottom of bicep, through the elbow, along the lower forearm, and branching into the fourth and fifth fingers. As it crosses the elbow, it travels through a channel called the cubital tunnel, which runs between the humeral and ulnar heads and between two muscles in the forearm. Contrary to logic, this tunnel is the most vulnerable part of the ulnar nerve, protected by just a thin layer of skin as it becomes sandwiched between the bone and outer skin. The cubital tunnel becomes particularly exposed as the elbow bends, allowing for a knock to impact the ulnar nerve directly. This is your funny bone. Why is it called the funny bone? There are two working theories. It could have caught on because the bone above is the humerus bone, and people were seeking comfort from puns after smacking their elbow on a door. Or it could simply be a reference to the strange feeling in the arm after hitting it. Why does hitting the funny bone hurt so much? As humans, our bodies do a great job of hiding nerves behind muscle and bone, protecting them from impacts that would damage the nerve and leave the recipient muscles incapacitated. This protection system is certainly not foolproof – if you extend the arm, a bunch of nerves called the brachial plexus at the front of your shoulder is exposed and some martial arts use this as a point of weakness in fighting. However, most of the time we can avoid taking hits to nerve clusters thanks to trusty ol’ evolution. In unfortunate circumstances, the exposed ulnar nerve can take a direct hit. The hit contacts directly with the nerve fibers, compressing them and temporarily preventing the brain from transmitting signals to the innervated muscles down your arm, creating that fuzzy feeling throughout the forearm. Alongside the lack of nerve signals, pain shoots down the nerve and you feel the hit not just at the site of damage, but in the forearm and hand too. The only comfort is that the pain will subside after around 30 seconds, and no permanent damage will be done. If pain persists and doesn’t seem related to an injury, however, you could have cubital tunnel syndrome. This feels similar to hitting your funny bone, including pins and needles in your ring and pinky fingers and weakness in the arm, but will persist for long periods of time. If this is you, contact your doctor. Source
