The cephalic phase of gastric secretion occurs even before food enters the stomach, especially while it is being eaten. It results from the sight, smell, thought, or taste of food, and the greater the appetite, the more intense is the stimulation. Neurogenic signals that cause the cephalic phase of gastric secretion originate from the cerebral cortex and in the appetite centers of the amygdala and hypothalamus.They are transmitted through the dorsal motor nuclei of the vagi and then through the vagus nerve to the stomach. This phase of secretion normally accounts for about 20 percent of the gastric secretion associated with eating a meal.
This enhanced secretory activity brought on by the thought or sight of food is a conditioned reflex. It only occurs when we like or want food. When appetite is depressed this part of the cephalic reflex is inhibited.
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