17.1 INTRODUCTION

Neurotoxicity is the term applied to a toxic effect on any aspect of the central or peripheral nervous system. Effects may be functional (behavioural or neurological abnormalities), biochemical, physiological, or morphological. It has been suggested that over one-third of chemicals may be neurotoxic in some sense. Behavioural effects are considered later in Chapter 18.

17.2 THE NERVOUS SYSTEM

The central nervous system (CNS) is the main mass of nerve tissue lying between the effector and receptor organs, co-ordinating the nervous impulses between receptors and effectors. The CNS is present in vertebrates as a dorsal tube, which is modified anteriorly to form the brain and posteriorly to form the spinal cord; these organs are enclosed in the skull and backbone respectively. In higher organisms, the CNS takes on an additional activity in the form of memory, which is the storage of past experiences.

The peripheral nervous system (Figure 17.1) connects with the CNS and is usually subdivided into two parts, somatic and autonomic. The somatic nerves supply voluntary skeletal muscles, giving control of movement, and also supply skin sensory organs. The acetylcholine receptors in the somatic system are activated by nicotine and similar compounds.

Figure 17.1: The peripheral nervous system showing the location of nicotinic and muscarinic receptors

The autonomic nervous system controls the involuntary activities of the body. There are two main parts to the autonomic nervous system: sympathetic nervous system (SNS) and parasympathetic nervous system (PNS).