The Circuit for Chemotaxis and Exploratory Behavior in Caenorhabditis Elegans
A wiring diagram of the Caenorhabditis elegans nervous system was constructed from serial-section electron micrographs 30 years ago. This wiring diagram divides the 302 neurons in the nervous system of the adult hermaphrodite into three overall classes: sensory neurons, motor neurons that form neuromuscular junctions, and interneurons that connect sensory neurons with motor neurons. Most sensory neurons and interneurons belong to bilaterally symmetric pairs with similar connections and morphologies, while motor neurons belong to larger classes. The C. elegans nervous system presents an exceptional situation in which neuroanatomical connections are extremely well defined and reproducible among animals. These detailed anatomical studies and a parallel genetic attack have increasingly been joined by functional and electrophysiological characterization.