Everyone has experienced salivation stimulated by the sight or smell of food. That response is an autonomic reflex, as is the act of swallowing following tactile stimulation at the back of the mouth. Many such autonomic reflexes coordinate activity in different regions of the digestive tract. Stretching the stomach with food, for example, stimulates increased activity in the colon, which can lead to the expulsion of feces.
The digestive tract is unusual in that it has an intrinsic (its own independent) nervous system. Neuronal messages can travel from one region of the digestive tract to another without being processed by the CNS. Of course, this intrinsic nervous system can communicate information to the CNS and receive input from the CNS; its important feature is that it can coordinate actions throughout the digestive tract without involving the CNS.
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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.