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In vertebrate species it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to every other part of the body.

Nerves that transmit signals from the brain are called motor or efferent nerves, while those nerves that transmit information from the body to the CNS are called sensory or afferent.

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.

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.

White matter includes all of the nerves, and much of the interior of the brain and spinal cord.

In the human brain, it is estimated that the total number of glia roughly equals the number of neurons, although the proportions vary in different brain areas.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.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.

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