Physical pain is felt by nerves in the body sending signals to the brain. Patients with spinal cord injuries who have the nerves of their lower body severed from their brain cannot feel pain in the lower body.
Not all nerves can detect pain. There are no pain receptors in the brain itself. There are two types of pain: chronic and acute.
Acute pain is roughly defined as short-term pain or pain with an easily identifiable cause. Acute pain is the body's warning of current damage to tissue or disease. It is often fast and sharp followed by aching pain. Acute pain is centralized in one area before becoming somewhat spread out. This type of pain responds well to medications.
Chronic pain is roughly defined as long-term pain or pain that is not necessarily associated with any form of injury or disease. This constant or intermittent pain has no known purpose, as it does not help the body to prevent injury. It often does not respond well to medications. Expert knowledge and/or skills may be necessary to treat chronic pain adequately. When analgesics are used indiscriminately, addictions to narcotics may occur.