Digestion begins with a cephalic phase that prepares the digestive system to receive food. When our brain processes visual or olfactory information about food, it triggers impulses in the cranial nerves innervating the salivary glands and stomach to prepare for food.
The cephalic phase is a conditioned or learned response to familiar foods. Our appetite or desire for a particular food modifies the preparatory responses directed by the brain. Individuals may produce more saliva and stomach rumblings in anticipation of apple pie than of broccoli. Appetite and desire are products of the hypothalamus and amygdala—brain areas associated with visceral processes and emotion. After the cephalic phase, digestion is governed by the enteric nervous system (ENS) as an unconditioned reflex. Individuals do not have to learn how to digest food; it happens regardless of whether it is apple pie or broccoli. The ENS is unique in that it functions (mostly) independent of the brain. About 90% of the communication are messages sent from the ENS to the brain rather than the other way around. These messages give the brain information about satiety, nausea, or bloating. The ENS, as part of the peripheral nervous system, is also unique in that it contains both motor and sensory neurons. For example, the ENS directs smooth muscle movements that churn and propel food al…
Core: Nutrition and Digestion
Caenorhabditis elegans is a microscopic, soil-dwelling roundworm that has been powerfully used as a model organism since the early 1970’s. It was initially proposed as a model for developmental biology because of its invariant body plan, ease of genetic manipulation and low cost of maintenance. Since then C. elegans has rapidly grown in popularity and is now utilized…
1School for Engineering of Matter, Transport and Energy, Arizona State University, 2Department of Neurology, Georgetown University Medical Center, 3Department of Pathology, Georgetown University Medical Center