a theory describing the experience of pain, which states when body tissues are injured, nerve endings, or nociceptors, in the area that is damaged transmit impulses to a particular area of the dorsal horn section of the spinal cord called the substantia gelatinosa. After these nerve impulses reach the substantia gelatinosa, one of two things can happen. If these sensations are sufficiently intense, then the signals are sent all the way up to the brain, where they are experiences as pain—the more signals that reach the brain, the more pain you experience. However, according to the gate control theory, not all of the pain signals carried by the nerve fibers will successfully reach the brain. Specifically, this theory posits that there is a gate in the substantia gelatinosa that either lets pain impulses travel to the brain, or blocks their progress, and any competing sensations that increases stimulation to the site could serve to block transmission. a treatment that affects someone even though it contains no specific medical or physical properties relevant to the condition it is supposedly treating. In other words, placebos are psychologically inert medicines or treatments that can produce very real, and even lasting, effects. The effects of placebos have been demonstrated on virtually every organ system in the body and on many diseases, including chest pain, arthritis, hay fever, headaches, ulcers, hypertension, postoperative pain, seasickness, and pain from the common cold.