Nervous System

The nervous system is the part of an animal's body that coordinates the actions of the animal and transmits signals between different parts of its body. In most types of animals it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS contains the brain and spinal cord. The PNS consists mainly of nerves, which are long fibers that connect the CNS to every other part of the body. The PNS includes motor neurons, mediating voluntary movement, the autonomous nervous system, comprising the sympathetic nervous system and the parasympathetic nervous system and regulating involuntary functions, and the enteric nervous system, a semi-independent part of the nervous system whose function is to control the gastrointestinal system.

At the cellular level, the nervous system is defined by the presence of a special type of cell, called the neuron, also known as a "nerve cell". Neurons have special structures that allow them to send signals rapidly and precisely to other cells. They send these signals in the form of electrochemical waves traveling along thin fibers called axons, which cause chemicals called neurotransmitters to be released at junctions called synapses. A cell that receives a synaptic signal from a neuron may be excited, inhibited, or otherwise modulated. The connections between neurons form neural circuits that generate an organism's perception of the world and determine its behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia), which provide structural and metabolic support.

Nervous systems are found in most multicellular animals, but vary greatly in complexity. The only multicellular animals that have no nervous system at all are sponges, placozoans and mesozoans, which have very simple body plans. The nervous systems of ctenophores (comb jellies) and cnidarians (e.g., anemones, hydras, corals and jellyfishes) consist of a diffuse nerve net. All other types of animals, with the exception of a few types of worms, have a nervous system containing a brain, a central cord (or two cords running in parallel), and nerves radiating from the brain and central cord. The size of the nervous system ranges from a few hundred cells in the simplest worms, to on the order of 100 billion cells in humans.

At the most basic level, the function of the nervous system is to send signals from one cell to others, or from one part of the body to others. The nervous system is susceptible to malfunction in a wide variety of ways, as a result of genetic defects, physical damage due to trauma or poison, infection, or simply aging. The medical specialty of neurology studies the causes of nervous system malfunction, and looks for interventions that can prevent it or treat it. In the peripheral nervous system, the most commonly occurring type of problem is failure of nerve conduction, which can have a variety of causes including diabetic neuropathy and demyelinating disorders such as multiple sclerosis and amyotrophic lateral sclerosis.

Neuroscience is the field of science that focuses on the study of the nervous system.

Read more about Nervous System:  Structure, Function, Development, Pathology

Other articles related to "nervous system, system":

Canine Brain Tumors
... Cancer of the nervous system is common in domestic canids, and includes primary neoplasia of the peripheral nervous system, primary neoplasia of the central ... Some of the most common of the central nervous system tumors are several types of primary (originating from brain tissue) canine brain tumors ...
Strongylocentrotus Droebachiensis - Anatomy - Internal Anatomy - Nervous System
... In the nervous system of sea urchins the spines, podia, and pedicellariae all act as sensors ... lateral canals of the water vascular system ...
Ctenophores - Description - Common Features - Nervous System and Senses
... Ctenophores have no brain or central nervous system, but instead have a nerve net (rather like a cobweb) that forms a ring round the mouth and is densest near structures such as the comb rows, pharynx, tentacles ... is determined by the animal's "mood", in other words the overall state of the nervous system ...
Sexually-induced Sneezing - Causes
... sneezing may be genetically determined, and may result from the way the central nervous system is wired "his reflex demonstrates evolutionary relics ... Sometimes the signals in this system get crossed, and I think this may be why some people sneeze when they think about sex." ...
Nervous System - Pathology
... article Neurology See also Psychiatry The central nervous system is protected by major physical and chemical barriers ...

Famous quotes containing the words nervous system, system and/or nervous:

    A two-week-old infant cries an average of one and a half hours every day. This increases to approximately three hours per day when the child is about six weeks old. By the time children are twelve weeks old, their daily crying has decreased dramatically and averages less than one hour. This same basic pattern of crying is present among children from a wide range of cultures throughout the world. It appears to be wired into the nervous system of our species.
    Lawrence Kutner (20th century)

    There are obvious places in which government can narrow the chasm between haves and have-nots. One is the public schools, which have been seen as the great leveler, the authentic melting pot. That, today, is nonsense. In his scathing study of the nation’s public school system entitled “Savage Inequalities,” Jonathan Kozol made manifest the truth: that we have a system that discriminates against the poor in everything from class size to curriculum.
    Anna Quindlen (b. 1952)

    The knocking out of a pipe can be made almost as important as the smoking of it, especially if there are nervous people in the room. A good, smart knock of a pipe against a tin wastebasket and you will have a neurasthenic out of his chair and into the window sash in no time.
    Robert Benchley (1889–1945)