The Nerve Impulse

The movement of an action potential down the axon is called the nerve impulse. The left side of the figure represents an unmyelinated axon, whereas the right side of the figure represents a myelinated axon. This is an excellent example of the important functional role of myelin. As you can see, the nerve impulse is much faster (indicated by the red highlighted area) in the myelinated axon. Myelin, created by glial cells, acts as an insulator by wrapping around axons. This forms a barrier to the flow of ionic current and prevents action potentials to occur. However, because there are gaps along the axon, called nodes of Ranvier, the action potential is triggered successively at each one. This jumping action, referred to as saltatory conduction, results in a much greater speed at which a nerve impulse travels.

See Tutorial 7 for additional information. For more detail on myelin, click here.

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