Nervous system special features

A special feature of the iris is its autonomic innervation. Sympathetic activation widens the aperture of the iris whereas impulses from the parasympa thetic nervous system decrease the aperture size. Therefore adrenergic agonists and anticholinergic compounds both increase the aperture of the iris, i.e., cause mydriasis, and antiadrenergic and cholinergic agonists decrease it, i.e., cause miosis. The iris can thus be considered an excellent mirror reflecting the balance of the autonomic nervous system in the body. " ... 

The individual unit of the nervous system is the neuron, a specialized cell that both receives and transmits information. The nervous system contains more than 100 billion neurons and is a major user of metabolic energy in the human body. It is also a region particularly susceptible to injury from toxic chemicals, lack of oxygen, and other assaults. Depending on the nervous region in which they reside, neurons may have different anatomical features and may use different chemical transmitters. Neurons communicate with each other and with their end organs by these chemical signals, which are released from the nerve terminal and interact with specific receptors on adjacent neurons or cells. 

Table 32.1 lists special features of the nervous system that may contribute to its sensitivity to CWAs. For example, the nervous system is comprised of different cell types interconnected by a complex communication mechanism dependent upon chemical transmission. Each of these... 

TABLE 32.1. Special features of the nervous system that contribute to sensitivity to CWAs... 

Different t5q>es of CWAs can affect one or multiple major organ systems. This chapter focuses on the nervous system as a potential target for CWAs. A brief overview of the nervous system, highlighting some of the special features that often contribute to its unique sensitivity to CWAs (and toxicants in general), will be provided. Specific information on the effects of selected CWAs on the nervous system will be discussed as well. 

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