Substance P is a neuropeptide, which is a type of molecule used by nerve cells to communicate. It plays a crucial role in transmitting pain signals from the body to the brain, making it important in the perception of pain. It is found in various parts of the nervous system and is involved in inflammatory responses. In addition to its role in pain, substance P is also linked to other functions, such as regulating mood and stress responses. It interacts with neurokinin receptors, which are proteins on the surface of cells that help transmit signals in the nervous system.