Nervous system

The nervous system is the part of an animal's body that coordinates its voluntary and involuntary actions and transmits signals to and from different parts of its body.

Central nervous system
The central nervous system (CNS) is the part of the nervous system consisting of the brain and spinal cord. The central nervous system is so named because it integrates information it receives from, and coordinates and influences the activity of, all parts of the bodies of bilaterally symmetric animals — that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish — and it contains the majority of the nervous system.

Peripheral nervous system
The peripheral nervous system (PNS) is the part of the nervous system that consists of the nerves and ganglia on the 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 spinal cord with the rest of the body. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain barrier, which leaves it exposed to toxins and mechanical injuries. The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system; some textbooks also include sensory systems.

Autonomic nervous system
The autonomic nervous system (ANS) is a division of the peripheral nervous system that influences the function of internal organs. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response and the freeze-and-dissociate response

Sympathetic nervous system
The sympathetic nervous system is one of the two main divisions of the autonomic nervous system, the other being the parasympathetic nervous system. The autonomic nervous system functions to regulate the body's unconscious actions. The sympathetic nervous system's primary process is to stimulate the body's fight-or-flight response. It is, however, constantly active at a basic level to maintain homeostasis. The sympathetic nervous system is described as being complementary to the parasympathetic nervous system which stimulates the body to "rest-and-digest" or "feed and breed".

Parasympathetic nervous system
The parasympathetic nervous system (usually abbreviated PSNS, not PNS, to avoid confusion with the peripheral nervous system [PNS]) is one of the two divisions of the autonomic nervous system, the other being the sympathetic nervous system. The autonomic nervous system is responsible for regulating the body's unconscious actions. The parasympathetic system is responsible for stimulation of "rest-and-digest" or "feed and breed"[2] activities that occur when the body is at rest, especially after eating, including sexual arousal, salivation, lacrimation (tears), urination, digestion and defecation. Its action is described as being complementary to that of the sympathetic nervous system, which is responsible for stimulating activities associated with the fight-or-flight response.

Somatic nervous system
The somatic nervous system (SoNS or voluntary nervous system) is the part of the peripheral nervous system associated with skeletal muscle voluntary control of body movements. The SoNS consists of afferent nerves and efferent nerves. Afferent nerves are responsible for relaying sensation from the body to the central nervous system (CNS); efferent nerves are responsible for sending out commands from the CNS to the body, stimulating muscle contraction; they include all the non-sensory neurons connected with skeletal muscles and skin.

Learn More

 * Wikipedia - Outline of the Human Nervous System
 * (video) Crash Course - The Central Nervous System (Central Nervous System)
 * (video) Crash Course - The Parasympathetic Nervous System (Parasympathetic Nervous System)
 * (video) Crash Course - The Sympathetic Nervous System (Sympathetic Nervous System)
 * (video) Crash Course - The Autonomic Nervous System (Autonomic Nervous System)