Radiotherapy: Also called radiation therapy. Radiotherapy is the use of high-energy radiation from x-rays, gamma rays, neutrons, protons and other sources to kill cancer cells and shrink tumors.
Receptor: A molecule inside or on the surface of a cell that binds to a specific substance and causes a specific effect in the cell. Receptors function much like gates or ports and enable pain messages to pass through and on to neighboring cells.
Repetitive stress injury: A muscular condition that develops when a person has to perform repeated motions in the course of normal work or other daily activities. Examples include writer’s cramp, carpal tunnel syndrome (from prolonged overextension of the wrist, like when typing) or tendonitis (inflammation of tendons).
Rheumatoid arthritis: An autoimmune chronic condition that causes pain and swelling in the joints. An autoimmune disease occurs when your immune system, which usually fights infection, attacks the cells that line your joints, making them swollen, stiff and painful. Over time, this can damage the joint itself, the cartilage and nearby bone.