Nerves known as nociceptors are distributed throughout the human body. When you cut your finger, for example, the nociceptors in that area send messages to the spinal cord about the injury. The spinal cord, in turn, sends neurotransmitters to the brain, indicating the extent of the injury. The neurotransmitters head first to the brain's thalamus, which forwards the messages on to areas of the brain that deal with pain and emotion. When the physical pain ceases, so do the nociceptors and neurotransmitters.
But our nervous system is not a simple circuit board that merely relays information between organs. Many variables exist in how we perceive and prepare ourselves for pain. For instance, over-the-counter pain relievers like ibuprofen or acetaminophen dull the effects of pain by reducing the chemicals that our bodies use to sense injury [source: KidsHealth]. They offer a good standby for headaches and sore muscles, but you'll probably need something stronger for a severe injury.
But if your doctor gave you a pill and told you it would make you feel better, it might work even if the pill had no medical ingredients. This is called the placebo effect, and it was discovered by army medic Dr. Harry (Henry) Beecher during World War II. He ran out of pain-killing morphine, but continued treating wounded soldiers, telling them that they were receiving morphine, when in fact he was giving them plain saline solution. Nonetheless, some 40 percent of the soldiers reported that the pain had eased [source: The Independent]. Later studies also have shown how a significant number of people who believe they are taking medicine get better even if they are actually receiving a placebo. The opposite also can be true -- patients who believe that their pain medication has been stopped begin to feel worse, even though they, in fact, are still receiving it. It appears that our brains have significant control over how we feel pain.
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