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The nervous system is composed of two divisions, the central nervous system (CNS) and peripheral nervous system (PNS). The CNS contains the brain and the spinal cord and the PNS consists of thousands of nerves that connect the spinal cord to muscles and sensory receptors.

A peripheral nerve is composed of nerve bundles (fascicles) that contain hundreds of individual nerve fibers (neurons). Neurons consist of dendrites, axon, and cell body. The dendrites are the tree-like structures that receive signals from other neurons and from special sensory cells that sense the body’s surrounding environment. The cell body is the headquarters of the neuron and contains its genetic information in the form of DNA. The axon transmits signals away from the cell body to other neurons.

Many neurons are insulated like pieces of electrical wire. This insulation protects them and also allows their signals to move faster along the axon. Without this insulation, signals from the brain might never reach the outlying muscle groups in the limbs.

The operation of the nervous system depends on the flow of communication between neurons. For an electrical signal to travel between two neurons, it must first be converted to a chemical signal, which then crosses a space of about a millionth of an inch wide. The space is called a synapse, and the chemical signal is called a neurotransmitter.

Neurotransmitters allow the billions of neurons in the nervous system to communicate with one another, making the nervous system the master communication system of the body.


Review Date: 5/22/2011
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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