11 The Nervous System

Abstract

I. INTRODUCTION
The nervous system is the most complex organ in Caenorhabditis elegans. In hermaphrodites the 302 neurons and 56 glial and associated support cells account for 37% of the somatic nuclei. In males the nervous system is more extensive; the 381 neurons and 92 glial and supporting cells comprise 46% of the somatic nuclei. The nervous system mediates a rich variety of behaviors, despite the small number of component neurons: Animals move forward and backward by propagating sinusoidal waves along their bodies; they perform exploratory movements with their heads as they feed; and they respond to a number of sensory stimuli, including mechanical stimulation, changes in the chemical environment, osmolarity, and temperature. Animals usually respond to changes in their environment with specific movements, but sensory cues are also important in regulating entry and escape from the dauer state (see Chapter 13), egg laying, and feeding. The differences in the number and types of neurons in hermaphrodites and males are reflected in sex-specific behaviors such as egg laying in hermaphrodites and the comparatively complex mating behavior of males.

In this chapter we discuss the structure and function of the C. elegans nervous system. Several different approaches have been used to investigate how this system functions. These methods include the use of reconstructions from electron micrographs of serial sections, histochemistry, and studies of the behavioral consequences of pharmacological agents, laser ablations, and genetic lesions.

Because of the small size of the animal, it is at present impossible to study the electrophysiological...