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Both autonomic and enteric nervous systems function involuntarily.
Nerves that exit from the cranium are called cranial nerves while those exiting from the spinal cord are called spinal nerves.
Among the most important functions of glial cells are to support neurons and hold them in place; to supply nutrients to neurons; to insulate neurons electrically; to destroy pathogens and remove dead neurons; and to provide guidance cues directing the axons of neurons to their targets.
A very important type of glial cell (oligodendrocytes in the central nervous system, and Schwann cells in the peripheral nervous system) generates layers of a fatty substance called myelin that wraps around axons and provides electrical insulation which allows them to transmit action potentials much more rapidly and efficiently.
Immediately behind the brain is the subesophageal ganglion, which is composed of three pairs of fused ganglia.Recent findings indicate that glial cells, such as microglia and astrocytes, serve as important resident immune cells within the central nervous system.The vertebrate nervous system can also be divided into areas called grey matter ("gray matter" in American spelling) and white matter.Typically, each body segment has one ganglion on each side, though some ganglia are fused to form the brain and other large ganglia.The head segment contains the brain, also known as the supraesophageal ganglion.