Introduction
There are many technical things to explain pain and painkillers, but I will explain the process and definition straightforwardly.
Let's suppose you are enjoying yourself on the beach, and suddenly, sand or dust particles enter your eyes. How could you know that dust went into your eyes? For sure, because you do not see correctly and feel uncomfortable. You are feeling pain; you let your enjoyment postpone and go to the washroom to flush your eyes with water. You keep washing your eyes with water until the dust is clear. But how did you get to know that the dust has been cleaned? Because now you are not feeling pain or feeling less pain. It is a fantastic thing that we take for granted. We can learn many things from this story.
Pain and painkiller
It is not good if we don't feel pain after an injury. For example, in a hockey match, you got hit by a hockey stick on your leg, which caused severe internal damage. You will not know about the internal injury, but only the pain can tell you about the seriousness of your injury. If you don't feel pain and the damage is severe, your internal injury could be more dangerous. The primary function of your body is to keep you alive and to fix any problems if there are any. That's why the body has some system. Pain is one of them, and it is not a disease. The body uses it as a signal. Whenever you get hurt/injured, the body intentionally gives you pain, so you do something about your pain or go to the doctor. Mainly the body uses pain as a signal. Because it is more important to flush your eyes instead of enjoying as aforementioned.
How Does The Brain Identify The Pain From The Whole Body?
There is an alarm system in the whole body, and that alarm signal (cells) that take the movement from the body to the brain is called a Nociceptor. It only signals the brain when there is damage. When they become active, we feel pain.
If your arm got injured, the doctor put a bandage on it. Ideally, you should have been cured by this bandage, but the pain still exists and could be upset for you; that is why the doctor gives you some painkillers, so you don't feel the pain. These painkillers stop the nociceptor's work.
The painkiller doesn't know the exact location of your pain. It just sticks with all the nociceptors in your body, so they can't do their work.
Also read: Neuropathy Pain Relief.