system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What actually happens when your finger gets "jammed" and why does it hurt so much?
gpt
Your finger takes enough force that this force directly translates as pressure to the bones. The bones bump at the joints, causing a bone bruise at the joint. The injury can be accompanied by strain on tendons/fibers depending on how the injury occurred. 
     Pain is caused by the chemical response to the injury, and the nerve endings available to receive the signals. In your fingers, there are a lot of nerve endings, presumably (from an evolutionary standpoint) to allow for sensitivity and control. We use our hands for so much that it is good to be able to tell a lot about our environment from the hands. The greater number of nerve endings means a more intense response (pain).