[thedoc (OP)]

Rakesh asked the Naked Scientists:
   My nine year old is asking - What is pain sensation in pain area ? Basically how it's happening?
What do you think?

[evan_au]

It's a message saying "Don't do that again!".

At the cellular level, a stimulus (pressure, heat, cold, chemical irritant, infection, tear, cut, puncture or break) triggers nerve cells which fire off messages to the brain to tell you it hurts.

For sudden pain, the message is "Get me out of here!". In some cases, the spinal cord and lower brain can react before the signals reach the conscious brain, as an automatic reflex to get you out of the situation even quicker.

Later, the pain message is "Let me rest!". You need to allow an injury to heal, and if you do normal activities, you can keep injuring the damaged part.

Unfortunately, in some cases, the pain becomes a chronic (continuous) experience. Pain is felt, even though doctors can find nothing physically wrong to cause the pain. The mechanism is not understood, but it may have to do with faulty signals reaching the brain, or nerves that were rewired as a result of an injury.

See: https://en.wikipedia.org/wiki/Pain