Nervous System and Nerve Cells
Living matter has the intrinsic capability to respond to changes in environmental (physical, biological and chemical) factors. Single cell organisms such as Amoeba, Paramecium also respond to the environment, interact with it and generate appropriate responses with the advent of multicellularity and increase in the size of animals, arose the need for coordination and rapid conduction of information within the organism.
To fulfil this need, some of the cells in the multicellular organisms became more and more specialized, acquired particular ability for receiving environmental information, for conducting it through the organism and finally for generating appropriate responses. And thus a cell type, the nerve cell or neuron came into being. The neuron itself underwent further morphological and physiological specialisation resulting in the evolution of a great variety of neurons (nerve cells) differing markedly in size and morphological appearances according to the specialized job they were required to perform. These cells became organised in what is known as the nervous system.