Thursday, December 17, 2009

Little about Nervous System


When someone hit your body, where the pain come from? How our hand feel pain? What the thing under the skin that can felt pain? How our eyes senses a light, recognize a pictures? How our ears, converting vibration until we can hear a voice? Naa, may you can find the answer in explanation about senses below.  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.

Neurons are distinctive in a number of ways, but their most fundamental property is that they communicate with other cells via synapses, which are membrane-to-membrane junctions containing molecular machinery that allows rapid transmission of signals, either electrical or chemical.

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.
In the skin are cells of several types called receptors; each is especially sensitive to particular stimuli. Free nerve endings are sensitive to pain and are directly activated. The neurons so activated send impulses into the central nervous system and have junctions with other cells that have axons extending back into the periphery. Impulses are carried from processes of these cells to motor endings within the muscles. These neuromuscular endings excite the muscles, resulting in muscular contraction and appropriate movement. The pathway taken by the nerve impulse in mediating this simple response is in the form of a two-neuron arc that begins and ends in the periphery. Many of the actions of the nervous system can be explained on the basis of such reflex arcs, which are chains of interconnected nerve cells, stimulated at one end and capable of bringing about movement or glandular secretion at the other (Encarta).

source:
- www.iqbalali.com/2007/04/29/sistem-syaraf/
- wikipedia.com
- encarta 2006
- etc

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