The nervous system is divided into two major systems: central and peripheral. The Central Nervous System (CNS) includes the brain and spinal cord, while the Peripheral Nervous System (PNS) is made up of nerves that are connected to the brain or spine. The CNS functions to store memory, receive information from the sensory organs, process the data, and produce emotions and thoughts eliciting reactions to the information received. The PNS, on the other hand, is the transporting system connecting the CNS and sensory organs of the body.
The PNS is further divided into the autonomic nervous system (ANS) and the somatic nervous system (SNS). The SNS is responsible for voluntary musculoskeletal functions. The ANS is involuntary, hence is responsible for homeostatic control of body functions. The ANS is further divided into the Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS). The sympathetic system brings about the fight-or-flight response while the parasympathetic stimulates body actions in the resting mode.