Encyclopedia  |   World Factbook  |   World Flags  |   Reference Tables  |   List of Lists     
   Academic Disciplines  |   Historical Timeline  |   Themed Timelines  |   Biographies  |   How-Tos     
Sponsor by The Tattoo Collection
Nervous system
Main Page | See live article | Alphabetical index

Nervous system

The nervous system of an animal coordinates the activity of the muscles, monitors the organss, constructs and processes input from the senses and initiates actionss.

In animals with brains, the nervous system also generates and conducts thoughts and emotions. Thus it is the system that animates "animals" (sponges are an exception). Chemicals that target the activity of nerves generally are the most rapidly acting toxins, typically causing paralysis and/or death.

Table of contents
1 Anatomy
2 Vertebrate nervous systems
3 Nervous system diversity
4 See also

Anatomy

The nervous system consists basically of two types of cells: Rapid signalling within the nervous system occurs by two primary mechanisms:

Vertebrate nervous systems

For heuristic and other purposes, the nervous systems of
vertebrate animals are often divided into a central (CNS) and a peripheral nervous systemss (PNS). The CNS consists of the brain and spinal cord. The PNS consists of sensory pathways and motor pathways, the latter being divided into the somatic (voluntary) nervous system and the autonomic nervous system.

The somatic nervous system is the voluntary part of the nervous where it coordinates the movement such as posture and walking. The autonomic nervous system is the involuntary part of the nervous system where all of the internal maintenance is taken care of.

The autonomic nervous system is then divided into the sympathetic division and parasympathetic division. The sympathetic nervous system is responsible for the excitment that a person feels due to the increase of heartbeat. The parasympathetic nervous system, on the other hand, is the opposite of the sympathetic nervous system. This system is in play when a person is resting and feels relaxed due to the slowing down of the heartbeat.

Nervous system diversity

The nervous system varies greatly among living animals. Cnidarians, such as sea anemones and jellyfish, have a nerve net, in which the activation of any one neuron triggers a wave of activation across the entire network. These waves are both afferent and efferent, representing both the sensation of chemicals or touch as well as the stimulus of the animals' reflexive mechanical response.The worms and flukes of the phylum platyhelminthes possess a network of nerves that operates like a more conventional nervous system, but lack a brain. Annelid worms and tunicates have a primitive brain called a ganglionic mass, which is a bundle of several nerves. Based in part on commonalities in embryonic development among all chordates, the tunicate brain is believed to resemble the evolutionary precursor of the vertebrate brainstem.

See also


Nervous system
Brain - Spinal cord; - Central nervous system; - Peripheral nervous system; - Somatic nervous system; - Autonomic nervous system; - Sympathetic nervous system; - Parasympathetic nervous system;

Human organ systems
Cardiovascular system; - Digestive system; - Endocrine system; - Immune system; - Integumentary system; - Lymphatic system; - Muscular system; - Nervous system; - Skeletal system - Reproductive system; - Respiratory system; - Urinary system;