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The nervous system is the part of an animal's body that coordinates its actions and transmits signals to and from different parts of its body.Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago.In the insect nervous system, the brain is anatomically divided into the protocerebrum, deutocerebrum, and tritocerebrum.Immediately behind the brain is the subesophageal ganglion, which is composed of three pairs of fused ganglia.
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.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.Most nerves serve both functions and are called mixed nerves.
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.