What is the nervous system?

The Nervous System is the part of a body that coordinates the voluntary (conscious) and involuntary (unconscious) actions of the body and sends signals between different parts of the body. It consists of two main parts, the central nervous system (CNS -- the brain and spinal cord) and the peripheral nervous system (PNS -- everything else apart from the brain and spinal cord).

Central Nervous System (CNS) CNS is the part of the nervous system that integrates the information that it receives from the environment, and coordinates the activity of, to all parts of the body. It consists of the brain and the spinal cord.

Peripheral Nervous System (PNS) PNS is the part of the nervous system consisting of the nerves outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system (CNS) to the limbs and organs, essentially serving as a communication relay going back and forth between the brain and the extremities. The PNS consists of 2 parts: the somatic nervous system (controlling muscle) and the autonomic nervous system (controlling gland and organs).

Somatic Nervous System (SNS) This part of the PNS controls voluntary (conscious) control of body movements via muscles and skin.

Autonomic Nervous System (ANS) The ANS is the part of the peripheral nervous system (outside the brain and spinal cord) that acts as a control system, functioning mostly below the level of consciousness (involuntary or automatic), and controls visceral (organ and gland) functions. The ANS innervates every organ and gland in your body. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, the diameter of the pupils, urination, and sexual arousal.