system
Given the following post, respond as if you're commenting on Reddit:
human
What exactly happens when you hit the Ulnar Nerve (aka Funny Bone)?

Hey Reddit, I was wondering if you could help me out with this one. I know how a nerve is stimulated, and how action potentials are propagated down nerves to send signals, but what I don't understand is why when you hit your "Funny Bone" it only sends those signals one way (towards the hand, where the nerve continues/innervates). 

My main question is: 

Does anyone know why this pain doesn't shoot up the arm and towards the body? I can't find it in any textbooks, I can only find why it shoots down the arm/towards the hand. If you're pinching that ulnar nerve, why wouldn't it cause pain up AND down, or even just more localized than sending the signal down?

Thanks Reddit!
gpt
When the ulnar nerve is hit with force in the elbow region, most of the nerves that are passing through that point are stimulated. This means that the nerve sends a signal to the brain, which is interpreted as pain/dysaesthesia in the region the ulnar nerve innervates. 
This is why you feel part of your hand tingling. Not because the nerve sends signals to the hand, but because it sends signals to the brain. Nothing happens to the hand, it is just your brain misinterpreting phantom signals from the ulnar nerve.