The autonomic nervous system orchestrates the functions of internal organ such as the heart and gut, serving as a connection between the brain and the rest of the body. It is classified in two divisions—the sympathetic and parasympathetic systems, often described as the body's accelerator and brake, respectively. For example, the sympathetic nervous system activates the "fight-or-flight" response in reaction to danger, concentrating energy on immediate survival and halting less urgent functions