Pain

Pain occurs in various degrees, from dull and aching to piercing and intense. Acute pain is usually associated with tissue injury and, for the most part, occurs for only a short amount of time. Chronic pain, however, persists for long periods of time, even years after the injury that originally caused the pain has gone away. For example, severe burns can create scar tissue that can continue to cause excruciating discomfort. Certain disorders, such as arthritis or cancer, may also cause persistent pain. In the case of phantom limb pain, an individual may continue to perceive pain in an arm or leg that has been amputated as though the appendage was still there. The precise cause of phantom limb pain is unknown. One theory is that the nerve endings remaining after the amputation continue to process the electrical pain impulses. Other theories focus on the firing of spinal cord neurons and the intricate neuronal circuitry of the brain.

Specific types of pain include causalgia (caused by severe burning that injures the nerve fibers under the skin) and neuralgia (caused by factors like viral infections and nerve degeneration that damages peripheral nerves). Headaches are the most common of all pain and may be chronic or acute in nature. Vascular headaches, like migraines, are caused by the constriction and dilation of the blood vessels in the area around the brain. Tension headaches have their origin in muscular contractions and are usually associated with psychological factors such as stress and depression. Traction or inflammatory headaches, which account for approximately 2% of all headaches, are caused by diseases.