The nervous system (Figure ) has two components: the central nervous system (CNS) and the peripheral nervous system (PNS).
The Nervous System
The CNS consists of the brain and the spinal cord, which lie within the skull and within the spinal column, respectively; both are bathed in a special fluid called the cerebrospinal fluid (CSF) and are protected by enclosing sheaths called meninges.The meninges consist of three layers: the outer layer (dura mater), the middle layer (arachnoid layer), and the inner layer(pia mater). Below the arachnoid layer and above the pia mater is a space called the subarachnoid space, which is filled with cerebrospinal fluid.
The PNS consists of the somatic nervous system and the autonomic nervous system, which is composed of thesympathetic and the parasympathetic nervous systems.