system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does the arm feel like static when you hit your elbow on a corner?
gpt
At the elbow end of your humerus, there's a bit of a groove where your ulnar nerve passes over the end of the bone, so the nerve's pretty exposed there.  If you bang your elbow the wrong way, you'll hit that vulnerable nerve and pinch it against the bone, and it causes a bunch of spurious sensations from all along where that nerve is connected.  It serves most of your forearm and hand, so the whole area lights up.

Most of our big nerves are buried deep, where they're safe, but there just isn't a ton of room at the elbow joint so we've ended up with a bit of a vulnerability there.