The Nervous System

The nervous system is a highly complex and interconnected network of neurons and supporting neuroglia. Neural tissue is extremely delicate, and the characteristics of the extracellular environment must be kept within narrow homeostatic limits. When homeostatic regulatory mechanisms break down, under the stress of environmental factors, infection, or trauma, symptoms of neurological disorders appear. There are literally hundreds of different disorders of the nervous system. A neurological examination attempts to trace the source of the problem through evaluation of the sensory, motor, behavioral and cognitive functions of the nervous system. Figure A-25 introduces several major categories of nervous system disorders. Many of these examples will be discussed in the sections that follow. Table A-17 summarizes representative infectious diseases of the nervous system.