Development and Subdivision - Nervous System
The Nervous System - AnOverall View Development and Subdivision The nervous system serves information processing. In the most primitive forms of organization (A) , this function is assumed by the sensory cells ( A – C1 ) themselves. These cells are excited by stimuli coming from the environment; the excitation is conducted to a muscle cell ( A – C2 ) through a cellular projection, or process . The simplest response to environmental stimuli is achieved in this way. (In humans, sensory cells that still have processes of their own are only found in the olfactory epithelium.) In more differentiated organisms ( B ), an ad-ditional cell is interposed between the sensory cell and the muscle cell – the nerve cell, or neuron ( BC3 ) which takes on the transmission of messages. This cell can transmit the excitation to several muscle cells or to additional nerve cells, thus form-ing a neural network ( C ). A diffuse network of this type also runs through the human body and innerva