Nerves and the Digestive System
The Autonomic Nervous System includes the Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS). The SNS is responsible for the Flight or Fight response of the body. When we get scared, the SNS increases our heart rate and provides energy to our muscles in preparation for action. In order to provide more energy to the heart, lungs and muscle, it inhibits (slows or stops) digestion by directing blood flow away from the digestive tract. The PNS is responsible for stimulating digestion by increasing blood flow to the digestive tract. The PNS stimulates salivary gland secretion and increases peristalsis. This increases the digestion of food and absorption of nutrients.
The ANS controls digestive functions such as: secretion of saliva from the salivary glands, peristalsis to move food along the digestive tract, gastric acid production in the stomach, sphincter open and closing, hormone release from glands in the digestive system, and the storing energy in the form of fat.
Two types of nerves help control the action of the digestive system. Extrinsic nerves controlled by the brain cause muscle contractions that push food along the digestive tract. They also cause the stomach and pancreas to produce more digestive juice. Intrinsic nerves within the walls of the esophagus, stomach, small intestine, and large intestine react when their walls are stretched by food. They cause the release of substances that speed up or slow down the movement of food, and the production of juices, by the digestive organs.