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It was in the decade of 1960 that we became aware of how basic neuronal networks code stimuli and thus basic concepts are possible (David H. The molecular revolution swept across US universities in the decade of 1980.It was in the decade of 1990 that molecular mechanisms of behavioral phenomena became widely known (Eric Richard Kandel)." A microscopic examination shows that nerves consist primarily of axons, along with different membranes that wrap around them and segregate them into fascicles.There is an anatomical convention that a cluster of neurons in the brain or spinal cord is called a nucleus, whereas a cluster of neurons in the periphery is called a ganglion.There are, however, a few exceptions to this rule, notably including the part of the forebrain called the basal ganglia Arthropods, such as insects and crustaceans, have a nervous system made up of a series of ganglia, connected by a ventral nerve cord made up of two parallel connectives running along the length of the belly.A protoplasmic fiber runs from the cell body and branches profusely, with some parts transmitting signals and other parts receiving signals.Thus, most parts of the insect brain have passive cell bodies arranged around the periphery, while the neural signal processing takes place in a tangle of protoplasmic fibers called neuropil, in the interior.

The PNS is divided into a) somatic and b) autonomic nervous system, and c) the enteric nervous system. The autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems.

The nervous system derives its name from nerves, which are cylindrical bundles of fibers (the axons of neurons), that emanate from the brain and spinal cord, and branch repeatedly to innervate every part of the body.

Nerves are large enough to have been recognized by the ancient Egyptians, Greeks, and Romans, but their internal structure was not understood until it became possible to examine them using a microscope.

Grey matter (which is only grey in preserved tissue, and is better described as pink or light brown in living tissue) contains a high proportion of cell bodies of neurons.

White matter is composed mainly of myelinated axons, and takes its color from the myelin.

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