As long as the threshold is achieved, a full action potential is generated. This is how neurons transmit signals locally from one cell to the next. Other forms of communication travel longer distances. For example, hormones are secreted by cells that travel in the bloodstream to distant target cells. Insulin is a case in point. It regulates the flow of glucose in the blood by stimulating cells to take up and store glucose as well as inhibiting its production. At a higher level of organization, nerve signals cause muscle fibers to contract or expand. These are just a few examples of how organisms send and receive information at many different levels of organization.