Definition:
The central nervous system (CNS) and the peripheral nervous system (PNS) are structural components of the overall nervous system, while the autonomic nervous system (ANS) is a functional component.

Functions of the nervous system: The nervous system is specialized for perceiving and responding to events in the internal and external environments. An awareness of the environment is made possible by nerve cells called neurons which are highly specialized in the properties of excitability and conductivity. The nervous system is present throughout the body as it functions with the endocrine system to coordinate closely the activities of the other body systems. The four principal functions of the nervous system are: 1) Orientation of the body to internal and external environments; 2) Coordination and control of body activities; 3) Assimilation of experiences requisite to memory, learning, and intelligence; and 4) Programming of instinctual behavior (more important in vertebrates other than humans).

Clinical Information
Ataxia. Loss of motor coordination. It may be the result of various neurological diseases or genetic disorders.
Cerebral palsy. Pathology of the brain causing paralysis, uncoordination, and other dysfunctions of motor and sensory mechanisms.
Coma. Varying degrees of unconsciousness that may be the result of any one of a number of causes.
Neurological examination. Mental assessment following trauma to the CNS. Five categories: 1) mental status and speech; 2) cranial nerves; 3) the motor system; 4) the sensory system; and 5) reflexes.
Paraplegia. Permanent paralysis of both legs due to injury or disease of the spinal cord.
Quadriplegia. Permanent paralysis of arms and legs due to spinal cord injury or certain diseases.