The nervous system is divided into the central nervous system (CNS; brain and spinal cord) and peripheral nervous system (PNS; nerves connecting CNS to body). The CNS is protected by meninges and cerebrospinal fluid. Neurons are the basic functional units and have a cell body, dendrites, and axon. The PNS is divided into somatic and autonomic systems. The autonomic system regulates involuntary functions and has sympathetic and parasympathetic divisions.