system
Given the following post, respond as if you're commenting on Reddit:
human
If a knife cuts your finger, what is stimulating your pain receptors once the knife is gone (after the cut has been made)?

Obviously, a cut still hurts long after your skin is first broken, and I am wondering why this is.  Are nociceptors just programmed to keep firing for a specified time after receiving a strong stimulus?
gpt
Cell damage is one of the big ones. 

When a cell pops open, it releases stuff (e.g., endothelin, bradykinins) that shouldn't be outside of the cell. This stuff hangs around and causes pain. 

Another factor is the arachidonic acid pathways. In response to damage, cells will start to convert membrane lipids into things eicosanoids. These are a class of molecules that do a lot of things to regulate the injury response. One of these things is cause pain (they also help stop blood loss and recruit inflammatory cells to the area). The "function" of the pain is to let you know you are injured and keep you from messing with it (and thereby worsening the injury).

As an aside, it's these pathways that are partially blocked by NSAIDs like aspirin and ibuprofen.