Our nervous system makes us what we are. Personality, outlook, intellect, coordination (or lack thereof), and the many other characteristics that are unique to each of us are the result of complex interactions within our nervous system. Information is received from the environment by sensory receptors and transmitted into the brain or spinal cord. Once inside the brain or spinal cord, this sensory information is processed and integrated, and an appropriate response is initiated.
The nervous system can be viewed as a scale of structural complexity. Microscopically, the individual structural and functional unit of the nervous system is the neuron, or nerve cell. Interspersed among the neurons of the central nervous system are supportive elements called glial cells. At the macroscopic end of the scale are the large divisions (or parts) of the nervous system that can be handled and studied without magnification. These two extremes are not independent but form a continuum; functionally related neurons aggregate to form small structures, which combine to form larger structures, and so on. Communication takes place at many different levels, the end result being a wide range of productive or life-sustaining nervous activities.
D. Haines, et al., (Elsevier, 2007) WW
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