ABSTRACT
Nerve cells, or neurons, are specialized in the generation, integration, and conduction of incoming signals from the outside world or from other neurons and deliver them to other excitable cells or to effectors such as muscle cells. The nervous system, unlike other organ systems, is concerned primarily with signals, information encoding and processing, and control rather than manipulation of energy. A central nervous system can be distinguished easily from a peripheral nervous system, since it contains most of the motor and nucleated parts of neurons that innervate muscles and other effectors. The nervous system has two major roles: to regulate, acting homeostatically in restoring some conditions of the organism after some external stimulus, and to act to alter a preexisting condition by replacing it or modifying it. The nervous system is a complex structure for which realistic assumptions have led to irrelevant oversimplifications. The nervous system is a control system of processes that adjust both internal and external operations.
