So chemical changes in the environment around cells can influence the cells to carry out processes that ultimately lead to specific physiological responses. Now, beginning with that signal molecule that increases in concentration around that cell and ending all the way with that physiological response all the events that take place between these two points of time, this is what we call a signal transduction pathway. Transduction simply means we're passing that, that we're passing down that signal from one area to another area and we'll see exactly what that means in just a moment. So to go back to our bear example, when we see that bear we panic and we begin running. What happens is or one of the things that begins happening is the endocrine system and more specifically the adrenal glands that on top of the kidneys begins producing a specific type of signal molecule we call epinephrine. Epinephrine diffuses into the bloodstream then goes around the cells and so the concentration of epinephrine around the cells increases and that ultimately influences the cells to carry out specific types of processes that lead to that physiological response of running away.