Human feels pain because it is one of his survival instincts. Pain will give warning to the body that something dangerous is coming up. If the person is incapable to feel pain, it will be impossible for him to avoid accidents and react to dangerous situations. How do we feel pain? The answer is the human nervous system.
The human nervous system is composed of two important parts: the spinal cord that serves as a channel and the brain that sends and receives information. These parts work together to form the central nervous system. Sensory nerves and motor nerves, also parts of the nervous system, are components of the peripheral nervous system. Sensory nerves send information about the environment through spinal cord. This information is called impulse. The brain receives the impulse and sends back commands to the motor nerves. Then motor nerves send information of what actions to perform.
For example, you have accidentally poured a cup of hot water on your finger then you inched it away from the cup. Your sensory nerves will send impulse; your body has felt pain and your brain will send a command to move your finger away from the cup. Another example: You have stepped on a soft object and then the brain ordered not to respond. How does your brain know that it is not painful? Sensory nerves receive different impulses and send different information. This is how the brain interprets the situation whether the object we are interacting with will cause pain or not. Nociceptors are special type of sensory nerves. The nociceptors activate when the body feels extreme pain from actual injury. The same nerve activates when breaking of tissues occur. In situations where you are involved in an accident and acquired wounds, it is difficult for you to determine where your wounds are located.
Mostly, our brain will react more on the areas where we feel greater pain. There are also other circumstances when we unintentionally hit the edge of the door with our foot that we thought our skin tissues open and form a wound but when you looked at it, it was only a bruise. That is because only the inner tissues of our skin are damaged.