These article , will explain to us about Nervous System. A nervous system contain of a million nerve cells which have many type and form. The mechanism of nerve is like a chain, they chain one and other to give and receive aa signal. The main and most cells in the system is called neuron.
All animals more advanced than sponges have a nervous system. However, even sponges, unicellular animals, and non-animals such as slime molds have cell-to-cell signaling mechanisms that are precursors to those of neurons. In radialy symmetric animals such as the jellyfish and hydra, the nervous system consists of a diffuse network of isolated cells. In bilaterian animals, which make up the great majority of existing species, the nervous system has a common structure that originated early in the Cambrian period, over 500 million years ago (Wikipedia).
Vertebrate animals have a bony spine and skull in which the central part of the nervous system is housed; the peripheral part extends throughout the remainder of the body. That part of the nervous system located in the skull is referred to as the brain; that found in the spine is called the spinal cord. The brain and the spinal cord are continuous through an opening in the base of the skull; both are also in contact with other parts of the body through the nerves. The distinction made between the central nervous system and the peripheral nervous system is based on the different locations of the two intimately related parts of a single system. Some of the processes of the cell bodies conduct sense impressions and others conduct muscle responses, called reflexes, such as those caused by pain.
- encarta 2006
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