C. elegans feeding.

C. elegans feeding depends on the action of the pharynx, a neuromuscular pump that joins the mouth to the intestine. The pharyngeal muscle captures food-bacteria-and transports it back to the intestine. It accomplishes this through a combination of two motions, pumping and isthmus peristalsis. Pumping, the most visible and best understood of the two, is a cycle of contraction and relaxation that sucks in liquid from the surrounding environment along with suspended particles, then expels the liquid, trapping the particles. Pharyngeal muscle is capable of pumping without nervous system input, but during normal rapid feeding its timing is controlled by two pharyngeal motor neuron types. Isthmus peristalsis, a posterior moving wave of contraction of the muscle of the posterior isthmus, depends on a third motor neuron type. Feeding motions are regulated by the presence and quality of food in the worm's environment. Some types of bacteria are better at supporting growth than others. Given a choice, worms are capable of identifying and seeking out higher-quality food. Food availability and quality also affect behavior in other ways. For instance, given all the high-quality food they can eat, worms eventually become satiated, stop eating and moving, and become quiescent.