The mind and the body constantly communicate with each other to maintain health and proper functioning of organ systems. Disruption of mind-body harmony can result in disease. The tendency for body systems to maintain a constant physiological state is Choose...yin-yang homeostasis chi sleep . The brain affects health through a special group of nerves known as the Choose...autonomic nervous system neuropeptides parasympathetic nervous system hormones which controls such essential body functions as breathing, digestion, heart rate, and sexual arousal. Emotional upset is a frequent factor in the initiation of illness. The chemicals that allow the mind to communicate emotional changes to the body's organs are called Choose...hormones neuropeptidesreceptorsnervous system . When a state of mind is the underlying cause of disease, the resulting health change is referred to as Choose...an anxiety attack a phobic reaction a nervous breakdown a psychosomatic disease . However, even if an illness originates from some form of stress or emotional change, the physical symptoms are "real" and must be treated. Healing can also result from positive thoughts, feelings, and beliefs. For example, if a person believes strongly that something or someone can cure him, then that object or person is said to heal due to the action of the Choose...religious belief meditation placebo effect nervous system . For this reason, the effectiveness of a drug must always be tested against the effectiveness of an inactive compound.