The magnitude of a given physiologic response will be constrained by the level of arousal present when the response begins. If a response occurs when arousal is already high, the amplitude of the response measured from onset to maximum expression will be less than if the same response occurred during a median level. While there are differing opinions regarding this psychophysiologic principle, it can certainly be said that all biological systems do have upper limits in their potential for response, and ceiling effects can come into play. This is because compensatory systems mediated via the sympathetic and parasympathetic nervous systems work to limit response intensities. Additionally, concrete limitations may exist, such as the finite number of sweat glands establishes the maximum electrodermal response.