Another type of regulatory process frequently used in conjunction with negative-feedback systems is feedforward. Let us give an example of feedforward and then define it. The temperature-sensitive nerve cells that trigger negative-feedback regulation of body temperature when body temperature begins to fall are located inside the body. In addition, there are temperature-sensitive nerve cells in the skin, and these cells, in effect, monitor outside temperature. When outside temperature falls, as in our example, these nerve cells immediately detect the change and relay this information to the brain, which then sends out signals to the blood vessels and muscles, resulting in heat conservation and increased heat production. In this manner, compensatory thermoregulatory responses are activated before the colder outside temperature can cause the internal body temperature to fall. Thus, feedforward regulation anticipates changes in a regulated variable such as internal body temperature, improves the speed of the body's homeostatic responses, and minimizes fluctuations in the level of the variable being regulated— that is, it reduces the amount of deviation from the set point.
In our example, feedforward control utilizes a set of "external environmental" detectors. It is likely, however, that most feedforward control is the result of a different phenomenon—learning. The first times they occur, early in life, perturbations in the external envi ronment probably cause relatively large changes in regulated internal environmental factors, and in responding to these changes the central nervous system learns to anticipate them and resist them more effectively. A familiar form of this is learning to ride a bicycle with minimal swaying. Learning of this type probably explains many situations in which the error signals observed are extremely small or even unde-tectable despite profound perturbations in the environment.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.