When we hear something, for example, the sound does not travel from the ear to the brain. Rather, the sound impinges on specialized cells in the ear and the presence of the acoustic energy causes movement of particular cell processes that result in the opening of ion channels in the cell's membrane that in turn alter the membrane potential of the cell, resulting in movement of an electrical signal along a nerve to the brain and the subjective sensation of sound. The acoustic energy that impacted cells in the ear did not travel to the brain, it was the subsequently induced electrical signal that propagated. This pattern is common to the way the body reacts to every environmental stimulus - the body changes the environmental factor into a biological signal that, in turn, leads to some kind of a biological response. The stimulus causes detection, and detection causes the response. Consequently, there can be no response in the absence of detection. The process whereby detection results in a biological signal is typically called transduction.