If the food digestion process is controlled by the nervous system, it is called nervous control. The neural network in the wall of the human colon plays a major role in food intake and digestion. There is a hunger center in the hypothalamus of this brain. It regulates human appetite and food intake. Two nerves control digestion in humans.
1. Intrinsic plexuses: The nervous system that controls digestion by receiving stimuli from inside the alimentary canal is called intrinsic plexus. It is called enteric or enteric nervous system. The enteric nervous system is called the second brain of humans. It extends like a web in the walls of esophagus, stomach, small intestine and colon and receives stimulation from there. Two types of intrinsic neural networks control short reflexes.
(i) Myenteric plexus: It controls the contraction or peristalsis action of the smooth muscles of the digestive tract.
(ii) Submucosal plexus: It controls the secretion of chemicals in the digestive system.
2. Extrinsic plexuses: The nervous system that controls digestion by receiving stimuli from outside the alimentary canal is called extrinsic plexus. It consists of sympathetic and parasympathetic. It regulates the long reflex action of the digestive system. They release acetylcholine and adrenaline. Acetylcholine powers the flow of food and drink through the alimentary canal. Besides, it helps to secrete more digestive juices from the stomach and pancreas. Adrenaline relaxes stomach and intestinal muscles and reduces blood flow.