18 - Nervous System

Abstract

The nervous system is comprised of the brain, spinal cord, sensory organs, and a vast array of nerves that control thought, movement, heart function, respiration, vision, hearing, speech, smell, touch, and many other physiological functions. Neurotoxicity is defined as an adverse effect upon the structure or function of the nervous system following exposure to a chemical agent. Multiple neurotoxic effects can be induced by exposures to mixtures of lipophilic and hydrophilic chemicals at levels below those known to be neurotoxic for the individual chemicals. Toxic chemicals can cause a slow degeneration of the nerve cell body or axon that may result in permanent neuronal damage. Neurotoxic chemicals enter the body via inhalation, ingestion, and/or dermal absorption. These chemicals and their metabolites enter the bloodstream and are partitioned from there into body tissues. Neurotoxic chemical exposures can cause a number of neurodegenerative diseases (NDDs), which are those diseases in which the irreversible deteriorization of neurons affects movement and/or memory. These diseases include Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis (also called motor neuron disease), and multiple sclerosis. The chapter also presents case studies related to neurotoxic chemical mixtures.