Olfaction
Volatile organic molecules are sensed through olfaction. C. elegans can distinguish and respond to many volatile odorants through attractive or repulsive chemotactic behaviors. In some instances volatile compounds can induce both behaviors depending on its concentration. Olfaction studies in C. elegans has revealed a complex sensory system where only three types of neurons (AWC, AWA, and AWB) have been found to be responsible for processing over seven classes of volatile odorants, including alcohols, ketones, organic acids, sulfhydrals, and heterocyclic compounds. Detailed study of the molecular machinery behind odor reception has shown that each neuron controls a particular attractive or repulsive behavioral response, for example, AWC controls attractive chemotaxis responses and AWB controls repulsive chemotaxis responses. One distinguishing feature of C. elegans sensory system is that the sensory neurons are polymodal in their stimulus detecting ablility; that is, individual neurons in C. elegans express multiple odorant receptors allowing multiple sensory functions, whereas vertebrate neurons express a single receptor limiting their function to detecting a single odorant.